Vortec 4300 Engine Problems
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Chevy 4.3L Vortec Common Engine Problems

Jake Mayock

Meet Jake

Jake is a founder of 8020 Media and has been creating automotive content online since 2017. He has been the lead writer for Chevy Trucks and has transformed it from the old and outdated site it was into what it is today. Jake creates a ton of GM related content for the 8020 Media YouTube channel and specializes in Duramax and Vortec information but has a wealth of knowledge across all GM cars and engines. Jake believes the L5P is the best diesel on the market today.

The 4.3 Vortec suffers from common problems such as ICV valve and TPS sensor failure, intake manifold leaks, distributor failure, port injection leaks, engine knock, and excessive oil consumption from AFM.

In this article we are going to dive into each of the common problems in detail as well as discuss overall engine reliability of the 4.3 Vortec platform.

Engine Variants

LB1 (1985-1986 primarily in C/K trucks)
LB4 (1985-1995 in the S10, El Camino, and other non-truck vehicles)
L35 (1992-2002 in C/K, Blazer, Silverado, Sierra, and others)
LF6 (1996-2002 in S10, Sonoma)
LU3/LG3 (2003-2014 in Silverado, Sierra, S10, Blazer, etc.)

Different problems affect different variations of these engines so it’s important to understand which one you have as we will detail below what variants experience what problems.

Overall Engine Reliability

If you want to cut to the chase without reviewing the problems: the 4.3 Vortec is a very strong and reliable motor. It is capable of lasting up to and even beyond 300,000 miles. However, to make it to the 300k mark, you are likely going to replace the distributor, water pump, transmission, ignition control modules, and a handful of other parts numerous times. 

Chevy 4.3L Vortec Engine Problems

  • Idle control valve and throttle position sensor failure
  • Intake manifold gasket failure
  • Distributor failure and distributor cap
  • Central port injection leaks
  • Engine knock (primarily on L35 and LF6 1996-2002)
  • Excess oil consumption (primarily on LU3 from 2004-2009)

If you would rather consume this content via a video, check out the video I did on Chevy 4.3L Vortec Common Problems on our YouTube channel:

1. ICV and TPS Failure

The idle control valve (“ICV”) and throttle position sensors (“TPS”) are prone to failure on all 4.3 engines, which can result in poor idling, engine stalling, bad acceleration, and other low-rpm running problems.

The idle control valve sits on the throttle body and is responsible for adjusting the amount of air that enters the engine at idle, ultimately controlling engine idle speeds. At idle, the valve blocks a small amount of air from entering the engine, keeping idle RPM’s low. Once you begin to use the accelerator, it opens up allowing full air flow. Over time, from the large volumes of air that pass through it, the valve can get gunked or clogged up and being to function poorly, creating idle issues.

The throttle position sensor is responsible for reading how far down the accelerator pedal is pressed, and relaying that to the throttle body. Like the ICV, the throttle position sensor is mounted onto the throttle body and can wear down over time, get dirty, or completely fail.

Symptoms of Failing ICV and TPS

  • Rough idling
  • Engine stalling
  • Hesitation during acceleration
  • Hard shifting and lack of power
  • Lack of accelerator responsiveness
  • P0122 engine code (TPS sensor)

2. Leaking Intake Manifold Gasket 

The intake gaskets on the LB4 and L35 Vortec’s are very prone to going bad which results in engine leaks, overheating, stalling, etc.

The intake gasket sits between the intake manifold and the cylinder head. It is responsible for sealing engine vacuum, and also engine coolant. Most gaskets are made of rubber, or paper, and are subject to high pressures and high temperatures. Over time, the pressure and temperature exerted on the gasket can cause it to wither down, crack, etc. When this happens, you’ll start leaking engine coolant and lose engine vacuum, leading to performance and overheating problems.

As the intake manifold controls air-to-fuel ratios, leaking vacuum can throw these off and lead to the engine running very lean. The end result is poor performance, cylinder misfires, and possibly stalling. Additionally, you can begin to leak engine coolant down the cylinder block. The most noticeable symptom of this will be a low coolant light, engine overheating, or coolant puddles underneath your car.

Intake gaskets are known to start leaking as frequently as every 50,000 miles. We recommend inspecting for leaks frequently and replacing this every 80,000 miles or as it becomes a problem. 

Fortunately, most gaskets are less than $50. However, DIY’ing this is only recommended for people who have an intermediate level of experience.

DIY replacement guide: https://www.s10forum.com/threads/replacing-lower-intake-manifold-gaskets-w-pics.328484/

Symptoms of a Bad Intake Manifold Gasket

  • Engine misfires
  • Sluggish acceleration, lack of power
  • Lean or rich air to fuel ratios
  • Engine overheating
  • Low coolant light illuminating
  • Leaking coolant / dripping onto garage floor

3. Distributor Cap Failure

The distributor cap failing is a common problem across all Vortec engines. The Vortec distributor is responsible for providing the ignition coils with the electricity required to power the spark plugs and create combustion. Wires connect to the distributor, which has a mechanical piece inside that spins in a circle to generate the voltage for the coils.

In vortec engines, the problem stems with the cap on the distributor, not the actual distributor itself. The cap is made of plastic. And the distributor sits in a high-heat part of the engine with poor air circulation or cooling. The cap is prone to warping from the heat, which results in the cap rubbing against the distributor rotor button. This causes the rotor bushing to wear out and the distributor begins to no longer be able to turn.

The simplest option here to fix this problem is upgrading to a distributor that has an aluminum housing on it. There is virtually no cost difference compared to the OEM distributor and with the aluminum cap, you likely won’t have to replace the distributor again.

Symptoms of a Failing Distributor

  • Engine misfires
  • P0300 to P0306 engine codes (for misfire)
  • Engine is slow to start, or not starting
  • Poor idling, acceleration, etc. (usually caused by misfires)

In some cases, the distributor can be prevented from turning completely, which will prevent the truck from starting. In most cases, the distributor will still turn enough to power the car, but not enough for it to run properly, causing a ton of misfires.

4. Central Port Injection Problems – Bad Spider Injector

The L35 and LF6 Vortec engines from the mid-90’s to early 2000’s had a “central port injection” setup which is known as the “spider”. The spider system uses a central pump with 6 tubes connected to it that lead to each of the engine’s cylinders.

In the L35 and LF6 engines, the spider injectors are known to leak at the pressure regulator and at the supply and return lines due to a design fault. Outside of leaking fuel onto the exterior of the engine itself, it can cause excess fuel to get sucked into the engine. When this happens, you have excess fuel in the engine creating very rich air to fuel ratios. Like pretty much all of these other engine problems, this can result in engine misfires. Some of the fuel can go unburnt in the cylinder and then lead to premature combustion due to heat, creating a misfire.

Symptoms of Bad Spider Injectors

  • Misfire engine codes (P0400-P0406 and P0300 codes)
  • Long starting, hard cranking
  • Poor idle and running at low-rpm’s, but fine at high rpm’s

5. L35 and LF6 Engine Knock Problems

The 4.3 Vortec engines made from 1996-2002 (L35 and LF6) have been reported to have engine knock problems.

In a properly functioning engine, fuel burns in even pockets instead of all at once. The pockets burn in even timing, in sync with engine cycles. Engine knock occurs when the fuel burns unevenly and out of sync with the engine cycles. The fuel pockets going off at the wrong time can create a “knocking” or “pinging” noise which is the tell-tale sign of engine knock.

Engine knock can be caused by a ton of factors, such as low-grade fuel, bad spark plugs, carbon build-up, etc. Engine knock is terrible for your engines internals and can cause serious damage to the pistons and to the cylinder walls.

On the 4.3L vortec, the cause of the engine knock has not necessarily been figured out, still to this day. However, it sounds like most people have fixed the issue by replacing the pistons in the engine.

6. Excessive Oil Consumption on LU3 Engines

The newest 4.3L Vortec engine, the LU3, which was manufactured from 2003-2014 has been known to consume excessive amounts of oil. Owners have reported the car requiring two quarts or more of oil in between normal oil changes.

The excessive oil consumption is likely to be caused by the Active Fuel Management system. There is currently an opened class-action lawsuit relating to oil consumption for the 5.3L engines, but many of the 4.3L owners are claiming to have similar problems.

The Active Fuel Management “AFM” system is a feature added to increase fuel economy. The AFM system works by “turning off” certain cylinders to improve gas mileage. Most people have reported that disabling the AFM system will fix the oil consumption issues. However, it is worth noting that excessive oil burn likely won’t harm your engine, so long as you are topping the oil off as it gets low. It is mostly a nuisance.

Here is a guide on how to turn off AFM.

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124 Comments

  1. 2005 Chevy Silverado 1500 4.3 liter V6. Changed distributor,plugs, wire’s, distributor cap, rotor and still get a multiple random misfire. Went with a aluminum shaft distributor and still get a multiple random misfire. In my opinion the Chevy 4.3 liter V6 is the biggest piece of junk maid…. CHEVROLET SHOULD HAVE LEFT THE MOTORS ALONE…. OLD SCHOOL IS THE ONLY WAY TO GO…… PULLING OUT ALL THE COMPUTER CRAP AND THEN GOING BACK OLD SCHOOL 350

    1. I was offered a 350 bored 40 over for my vortec v6 4.3 and 200 dollars sounds like a good deal four-barrel carburetor pop-up Pistons and roller rockers and comes with a being named slapstick what y’all think

      1. Hell no. Keep that 4.3 and let everyone else keep sleeping on it. I could do without all the vacuum snip. But on a 1 -10 im giving the 4.3 a rock solid 10 ☆☆☆☆☆. You can’t kill it. The harder your run that little bad b**ch the more your going to prolong all the small internals. I had a blonde would say day…it was a couple 3 months. Early 20. I bet I ran my girl bone dry ,winter , singles and teens. Checked oil one day. Smoke rolled out the tube
        Oil baked on stick. Never heard a lifter peck,tink,think, nine. I said holy cow. Just for s’s n g’s. Before I did pass head I drained her. I thought sheer luck that was. 2 weeks work to amd from only. 12-38 miles a to b and back. And I shit you not. Fucker runs I ike a champ. She will jump on green. I say all the time. No its not an LT SWAP thats that 4.3.

        1. I agree the 4.3 has been a great motor. I have a 95 c1500 with a tired 350 last owner overheated it bad. I purchased a 97 4.3 truck with a 5 speed , I am dumping the 350 and 4l80 for this. The last 4.3 truck I had was 22 to 23 mpg. It sure beats the 350 at 16 mpg. I don’t tow heavy with it so I want the 4.3 gas milage and reliability.

          1. Had several 4.3 in my Chevy- 1994 and 2000 Chevy trucks both ran forever. They are work horses I love the v8 for power but for gas saving I take the 4.3 on trips

        2. Couldn’t have said it better. His name is Whitey! 🙂 Mines Got
          Earned his own spot in heaven. Baddest MF alive. Loyal thru the sh*t Show. Makes sure the show goes on… as it Must. Handz Down. As much sh*t as I give Him? He deserve to be an A,RsH’le!*×

      1. have a L35 4.3 litre 2003 Blazer ZR2. dead miss at idle but OK driveing. miss is on #6 cyl. new cap wires plugs good spark 195 compression valve train good n0 intake leaks. sound like a spider injector to you?

        1. I have a similar issue.
          In November 2021 I drove it too hard through some mountains. Going up and down steep grades and it was was very hot.
          It deva loss of power and a bad miss.
          After limping back to my town I lived in.
          I found oyt I was only hitton 4 cylinders.
          Turned out to be a distributor cap issue and a loss of compression in a cylinder?
          Replaced the cap and rotor, wires and plugs. Spent a considerable of effort using oil additives to flush and clean out the engine. This was done through several oil changes over a short period of a few months. I had was sounded like valve train clatter, somehow the valve train clatter stopped and it had just a low compression in the #3 cylinder. Runs very rich at idle and smooths out at 1,100 rpm. Runs fine in town. I put it into neutral most of the time at a stop light. As the idle is rough due to the dead cylinder at idle. Gas mileage dropped by 3-4 mpg in town. I replace the onboard computer, the ignition module. I recently replaced the cap and noticed a marked improvement in engine idle and overall performance. I used a very good oil additive in it last year. MoS2 Liquid Molly anti friction, oil treatment. My enging has a great of power, a miss at low rpm. I always change the oil at 3 month intervals. The oil always has tiny metallic particles in it at oil changes. I am at 178500 miles.

    2. Hi John to get to your issue. You need to have your fuel injectors checked,make sure your Throttlebody is clean . Are you using ac Delhi plugs beleave it or not makes a big difference. Hope this helps . Your friend Ray!

    3. I put in a bottle of red line fuel system treatment and followed up with a bottle of gumout regane high mileage fuel system cleaner. Misfires all gone. Sure I’ve changed the cap and rotor several times. That never fixes it. I got 403,000 miles out of a 1999 blazer 4.3L. You read that right, 403,000 miles. Regular oil changes and lots of highway miles. Not a lot of street driving.

    4. This random misfire p0300 is most likely being caused by leaking fuel pressure regulator located onset the upper intake plenum on the back of the spider injector assembly symptoms are as follows vehicle is usually easy to start when cold or sitting overnight allowing leaking to evaporate or pass by rings vehicle will be hard to start after running then shut down and waiting ten to fifteen minutes at that time fuel pressure had had a chance to leak past defective fuel pressure regulator causing a flooded condition however like carbureted models holding throttle open during cranking will allow starting clearing temporary condition but will require this regulator to be replaced when vehicle does start from fliooded condition it usually idles rough at first sheeting random misfire code then smoothed idle hope this helps you understand why random misfire p0300 usually occurs

      1. Once engine gets up to normal heat and I turn it off then it won’t start not getting fuel could it be a bad fuel pump just changed it out four months ago

    5. I had a 1998 Chevrolet WT-C-1500 with a 4.3 vortec engine never once had a problem with the engine running smooth or never misfire but had a lot of other stuff that kept it in the shop!

    6. Could be a short in the wiring harness or just a bad connector at the crank position sensor. Have a look at it and check the connection in the plug for grime and buildup.

  2. Do you have any pictures, web links, and YouTube videos that can show me exactly where the knock sensor is on a 4.3 L 2002 Silverado pickup?

    Also, the check low oil sensor/ float that is in the oil pan, I cannot locate that either.

    Thanks, Carl ✌🏻

  3. Could be your coil.i also changed cap rotor and button but still had multiple miss fires.cleared up when I installed new coil.fyi

  4. The aluminum distributor I bought was 20 degrees retarded and my engine misfired until I ground the hold down and now it runs good. The mass airflow sensor can make it misfire also.

  5. I have a 1997 Chevy 1500 5 speed v6 with 330,000 miles on it. Nothing ever been put on except a slave cylinder. everything on it just as it came from the factory except radio and tires.

  6. I have a 2000 blazer 4 door/4×4, 4.3l bought 1 year ago had new cap/rotor/wires/plugs.only put 3200 mi in 14 mos.began very slight accel buck sometimes. a week ago wouldn’t start coded multi misfires.put new coil-ign. cont. module, started right up ran perfect for 4 days, then driving to store bucking then loss of power like staving for fuel.got off road, then no start or firing. Only codes i have ever had were P0440,for long time ran great. then went no start most recently the miss fires. HELP.

    1. At the bottom of the engine in front in the timing cover is a speed crank sensor type plug- unplug it clean the oil off and reinstatll the connection. Should fire right up.

  7. Had something similar happen. Turned out one of the wires leading to the ignition coil separated inside the insulation about 3″ from the coil connector where the wiring makes a sharp bend. Check if the coil is firing. Could be the same problem.

  8. I have a 2014 4.3 chevy siverado purchased used from a dealership. 63000 miles no problems yet. 4 wheel drive 1500, so fare it has been a good truck. It is my daily driver. I had a 2001 ford 150 with a v6 it was a good truck to with 400000 miles. I hope the chevy will be as good.

  9. i have a chevy g-10 cargo van, starts well, seems to run well going down the road, but it can stall from a start like a stop sign or something similar. a mechanic advises the mechanism that holds the choke hooks to is worn out and may be the culprit, your input would be appreciated , i have also been told to just buy a new carb but its hard to find a new rochester 4 barrel carb for the 1986 4.3 vortec

  10. I have a 1996 chevy blazer, it overheated and it knocking hard I think it is a value rod but I still don’t know what causes the overheating. the thermostat still works the fan spins and the coolant is full. but I was reading the intake gasket part. if anyone has any other ideas please reply trying to get it up and running for my son for his first car.

  11. my 1995 is running rough idie and burning rich i did a tune/up i put a good rotor and cap on.I it got a bad mess and iwas told it could be a fuel regulator bad spiders and it will 500 1000 to fix iff i keep driver it it will wreck motor let me no ty.

  12. I have a 95 gmc sonoma 4.3 v6 2 wheel drive it has 353,000 miles I was at the car wash as I got done spray the truck off it started idle high and shifted hard when i put it in drive when two tenths of mile and parked and it started idle really high so I shut it of went to start back and it will not hit i have spark,fuel,charged battery,cap,button,wire plugs, what would it be it spin over really fast and its the truck with the z in the vin

    1. Timing chain or something like that I think happened to me was knocking really hard and gave it gas and it shifted and died now won’t crank back up ????

  13. A vacuum leak can cause a “random misfire.”

    Due to a vacuum leak, the air-to-fuel mixture is too lean (too much air and not enough fuel).

    In some situations where there is a vacuum leak, a properly operating Mass Air Flow sensor (MAF) is sending correct air-to-fuel-ratio information to the Power-train Control Module (PCM), but the intake manifold is sucking a different ratio because the vacuum leak occurs after air passes through the MAF.

    Additionally, sometimes when rounding curves, or going over bumps, or during highway lane passing attempts, or during accelerations, but most often during moderate accelerations, such as when merging onto a freeway from the entrance ramp, you may get the flashing “Check Engine” light.

    This indicates a random misfire, and one which has been caused by a vacuum leak.

    Before you throw in the towel, you gotta check for vacuum leaks!

  14. I bought my 1999 Silverado used in 2004. It is unusual in that it has a 4.3 ltr. V6 with standard cab, long bed, premium sound system with surround sound, and a factory towing package with electric trailer brakes, bed cover, and 4 wheel drive. The truck had 98,000 miles on the clock. The truck pulled my 4,700 lb. Boat and trailer from lake Superior to Dallas Texas, from Dallas to Minneapolis Minnesota., and back again with no worries. The truck has 245,000 miles now. The only problems I had were:
    1. Water pump leaking
    2. A/C compressor failed
    3. Intake manifold water leak.
    4. Fuel pump failed.
    5. O2 sensor failed.
    6. Radio CD player died
    7. Heater/AC blower motor failed.
    8. Replaced entire brake system due to corrosion and fluid leaks.
    Overall this truck has been a great truck. I get compliments offers to buy it all the time.

  15. Man oh man this truck has been a whopper for me….for sure!
    It’s an 05’ single cab Silverado short bed 4.3L, “Base model” with a factory cd player & am/fm radio, factory power door locks but with factory manual windows & without he keyless remote entry system. I bought it from my father in law (1 owner) in 2014/2015 with about 115k miles on it. At about 175k miles in 2018 I decided to run some sea foam through itband give it a basic tune up. Ran good the day of snd night of the tune up.
    Next morning it fired right up but with a horrible idle & an instant CEL:/ MIL check engine light showing random misfire &/cyl.’s #3 & #5 missing. Okay, so then I dive into it after work.
    After months of troubleshooting everything & then replacing everything electrical except for the wiring harness, my temper and frustration eventually get the best of me & I broke down…….& bought a reman’d engine and reman’d tranny thinking, “Well hell,…. I’ve already replaced the center console lid, the headliner, the AC/Heater ventilation control panel & switches & wiring along with the front brake calipers, front rotors, both Front wheel hub assemblies & ABS wheel hub sensors,. Both front coil springs front Upper & lower control arms, tie rods and all 4 shocks. All new sensors under the hood, new distributor cap and rotor, new plugs , new plug wires, new ignition coil, new alternator, new thermostat. Other than the electrically body harness and everything else that bolts to the motor. Then still fought the same missfire issues for another couple of months. Then I started tearing down the top end to see if I’m missing something. Nope. Then comes the reman’d engine. Boogered up the oil pump rotor assembly installing the engine and long story short I bought and installed the replacement parts for what I broke and then also bought a reman’d tranny.
    So the new motor and transmission are installed. And still Im facing the same problems to today.
    Truck fires up. I mostly get the p0200 and p0300 codes with some random p0016 or p102 codes. It is essentially a beat up (on the outside) looking but brand new everywhere else truck. Still checking/adding ground wires and troubleshooting the wiring harness.
    Parts$$$
    Tools$$$$
    Time$$$$$$$$$$$$

  16. I had a Chevy c1500 w/t with the 4.3L vortec engine in it that lasted up to 415,573 miles on it and it was all original parts only thing I changed was tires, radio, and a starter. That’s it. I honestly believe that the 4.3l’s are the best motors made and are really strong motors. I think just like everything else somethings might go wrong with some of the 4.3 motors because nothing is perfect even machines have imperfections with them and you just might be that one in the haystack that gets the malfunctioning one but I’d like to say that 90% of them are great motors overall. But these are just my opinions. And like I said my Chevy 4.3 drove till 415,573 miles on it and it was still running just started to be rough idle so I scraped it and got another 4.3 Chevy 1500 love it.

  17. @ Dodsonsays
    For sure they are great motors. It’s the electrical issues within the factory design that I appear to be battling.
    Right now the P0200 code is my nemesis.
    P0200 = (Per Haynes/Chilton) “Fuel Injector Control Circuit, incorrect voltage”
    P0200 = (Per the OBDII scanner manual) “Injector Circuit Open”
    I’ve added grounds from head to head to the body ground. And from DS head to DS block to the chassis. From Battery Negative to original location next to the starter motor and from Battery negative to the front cross member chassis.
    Battery Negative to Block, done.
    Block to chassis, done.
    Block to body, done.
    Still the same P0200/(pd) & P0300/ (pd).
    I’ve stripped the wiring harness from the fuel injectors back to the ECM. I also went and bought some 4 gauge & 8 gauge stranded wiring to replace some of these grounds.
    Information is limited online as to the best & correct ground wire locations. Almost no information.
    Just ordered me the Ancel FX9000 diagnostics scanner tool on Amazon. Needless to say if it doesn’t pinpoint the electrical issue or other issue(s) if it is something else, then I’ll be returning it.
    I’m open to any knowledge that is willing to be shared.

    1. Having same issues. Did you ever get it fixed ? I would appreciate any help or information as to what you did to fix it . Ty

  18. Hello
    i have a 2003 Gmc 1500 Sierra with a blown 4.3 262.
    I’m uncertain where to proceed in order to optimize to a upgraded shortbock.
    advice and links would be greatly appreciated

  19. Matthew I really believe what you should have done from the start was check your injectors. Not the wiring. The one thing you did was internal.. the seafoam. If it’s just a coincidence then I’d be looking at the ignition module or the computer. The injectors fire because of the ignition module knowing what cylinder position and it controls the ground and closes the circuit. Some vehicles moved that function to the computer..I haven’t ever looked at that problem on the 05. But if it has an ignition module and injectors first.

  20. The basics of the engine mechanical design is sound, Replace the manifold and a carburator and ignition with a HEI and the engine will be reliable. The GM AFM and newer DFM fuel control systems are prone to fail, causing total engine fail. I work on this junk, Just another reason to have a older vehicle with no electronics.

  21. Random misfires solved. Original spider injectors have pop it valves that cannot take the ethonal fuels. New Delphi or GM multi port injectors designed to handle the new fuels. And an Accel coil with 48,000 volts instead of stock 41,000 volts helps. E3 spark plugs #62 will burn fuel complete. Modify the throttle body plate by removing the extra 1/4 moon shaped piece on the bottom of it. It restricts 25% of the air flow, big-time. Cold air intake, exhaust headers, 2-1/2″ pipes into 3″ Y , 3″ into flowmaster 50 muffler with 2 2-1/2″ duel out the back. Tuner. Transmission has 1800 stall torque converter, after market shift, oversized clutches & bands, and a 65 pinion instead of stock 60. All set up in 98. S-10 blazer…Zr2. ….0 to 60 in 5.7sec.

  22. 02 Silverado every time it rains have to change the cap and wires! Dodging puddles isn’t always easy !
    Definitely a dry weather only vehicle, what can we do to flipping fix this?

      1. I bought new wires for mine,a good brand,but they were arching all over the place,
        So I had warranty, I got another set,but this time I wrapped them with electric. Tape,no more problems!

    1. I have a 05 Silverado and every time it rains truck runs like crap like it has no power but done it since I’ve had it

      1. You likely have a bad coil pack or bad wires. Trying spraying them with water (use like a spray bottle) when it’s dry outside and see if it does the same thing.

  23. Have a 2004 chevy silverado 1500 2wd 4.3 v6 and one day I had everything off and woke up the next morning and it cranks but it won’t start

  24. could someone please tell me which parts i would need to convert to carburation a 2000 Blazer 4.3 that someone installed on an S10 previously with a 4 cylinder. It has not run since this was done, security comes up, i have to reprogram and after a few tries it comes back. All it does is start and die within seconds. Is the tank fuel pump also the same or do I have to change it to one for a 4.3. I do not want any computer on the engine, the whole chassis is being put under a 1953 Buick Special and i want it to run and be as simple as possible. So what do I need to get to make the change. Please answer me at OhRobocop and the mails is to aol.com. Thanks.

    1. I would definitely change fuel pump. orig. pump pressure will be way to high for carb.

      1. Add a pump output return bypass line ahead of the carb AND have a flow control valve there. Dial more fuel in ..with inline pressure guage. & when it decides to run good., record thr pressure. Go from there.

  25. 1994 Olds Bravada/Blazer 4.3L Vortec black engine. 155K Have had to do the TPS, Spider injector and fuel pump but that is it, other than regular maint. I upgraded the leafs in back and it will tow as much as a 1/2 ton, especially with the AWD. I have been saving the vehicle to pull the 4.3 and put it in a sand rail and convert the body to electric, plenty of space where the gas tank wont be… Great engine!

  26. I have a 1992 Chevy Cheyenne 1500 with the 4.3l V6…I’m running rich and burning spark plugs wires weekly…I’ve repaired vacuum leaks, throttle body gasket, fuel filter, and I’m still misfiring and running rich. I have hesitation on take off and poor acceleration….not sure what to try next.

  27. I’ve got an 03 1500 2wd 5 speed 4.3. I’ve been having an issue with it running rich. And at a certain rpm range (2000-2500ish) it jerks and hesitates pretty bad but with further acceleration it clears up and runs smooth. Not sure what it means but also running the ac compressor makes it worse. Doesn’t seem to matter wether it’s up to temperature or not. I’ve replaced 02 sensors, tps, plug wires, cleaned throttle body. Also it got so bad it wouldn’t run and my dad unplugged the map sensor and it at least would run and has without it for probably two years. If anyone has any ideas on what to check I’d appreciate it

  28. My 2011 Silverado 4.3 vortec ran no oil pressure we changed the oil pump that didn’t help so we tried the sensor it seems dry any recommendations where to start next

    1. Did you try the oil pressure sending unit ? If not its located on the back of the motor to the right if standing in front of vehicle with hood popped open. Just behind coil packs , closer to firewall, hard to see but you can change it out if you have a mirror to help you see, cheap part & well worth the shot $ 20.00 here in ohio. HOPE THIS HELPS

  29. I have a 97 2wd 4.3 and my truck doesn’t seam to be getting fuel. I’ve replaced…. fuel filter, Fuel pump, cap, rotor, plugs, wires, crankshaft positioning sensor, both temperature sensors, idle are control valve. Mass airflow sensor, air filter, new acdelco injector system and I’m just going broke trying to get back to work. Please help me. Starts with carb cleaner. Has good fuel pressure. Has good timing

  30. I have a 2003 Safari. Every time I go up a hill it missfires and at least one cylinder drops out. Every time. Check engine light flashes goes to limp mode until I let off the accelerator. Then it will stop flashing and shift into overdrive. I have tried everything. HELP

      1. I have no check engine light for almost 2yr
        On 4.3l chevy 1500 but still codes in memory po171 and po174 l called the codes Evil LoL 🥴🤔😊

  31. I have 2004 safari and it will crank but not fire (or start) after a rain storm. After weather dried up engine would start right up. Replaced distributor cap, then ignition module, then coil. Plug wires and plugs been replaced. Now it seems the precipitation over night causes same problem. After a few hours of drying out it starts right up. Somethings getting wet? Please help. I wearing out of pulling the cowling.

  32. 2000 Astro, 4.3. P0305
    HISTORY
    I’ve replaced 1 water pump, 1 power steering pump (my fault – I damaged it), 1 Hydro-Boost unit, 1 intake and plenum gasket set for coolant leak), 1 new version injector spider, plugs are new AC DELCO Iridium, plug wires are new, new cap/rotor, cam position sensor replaced while I was in there anyway because it’s a van and I HATE taking that doghouse off-and-on, and 1 crank position sensor since it was leaking oil,

    Years ago I ground the distributor hold down to allow the distributor to move from factory -22° ATDC timing to 0° and immediately increased fuel mileage from 18.8 MPG to 23 MPG!.

    Even after all that, it’s still getting a P0305 and flashing SES. It’s my wife’s car and she’s afraid to drive it and is constantly taking my Trail Blazer. That has to stop! She moves my seat, steering wheel, mirrors, HVAC settings and the worst part …. she changes my radio settings!

    I know the fuel pressure regulator is over #6 cylinder intake runner, so it’s not causing P0305 if it was leaking and I’d find it hard to believe it’s leaking since it’s new-ish and it only happens after a hot-soak in the Astro dog house.
    .
    This only happens like I say — after restart from hot-soak (eg: a 1/2 hour shopping trip and at restart, then the code pops). You can drive from Montana to New York if you just don’t shut the engine off … without any codes at all!

    #1 on my want list is I want my car back 100% of the time ’cause my mirror adjustment motors are complaining.
    #2 on my list is that now SWMBO wants a new car. That ain’t gonna happen until after the computer chips availability on new cars drive the prices down again and a new car isn’t likely even then. .
    #3 on my list is that I’m a retired ex-mechanic with 55+ years experience and this is destroying my credibility and stature not only at home, but in the neighborhood.

    Help a guy out …. huh?

  33. 2010 4.3 serria 99,500 miles.it runs great but burns alot of oil. Thought it might be pvc valve. But thier is no pvc valve on this truck. Just a metal tube that looks like one.

  34. Same problem here. 2003 s10 4.3. Random misfire. Replaced the distributor (aluminum shaft), cap and rotor, coil, plugs, injectors , mass air flow.. fuel pressure is 58 psi. Still getting a po300 and runs like crap if it will run at all. Oh and it only has 78000. Any ideas?

  35. I have a 2000 vortex 4.3 with three hundred and thirty eight thousand miles just replace the starter and other parts normal ware and tear, run like a top and straight down the road . And worked it hard with lumber packages,bought it new for nineteen thousand , very happy customer go Chevy and Brandon.

  36. I have a 2003zr2 blazer that at the moment has only one issue that bugs me and it’s not a continual one.it happen when cruising at any speed really and occurs when you give it the gas from the cruise speed….I don’t have cruise control set…..just pedal feed.when it occurs it feels like it momentarily shut off then takes off…..when it shuts off or whatever it is it feels like the driveline takes a hard jolt then takes off.ironicly it’s not a all the time thing but if it happens once it will then repeat itself several times til you park it for a while

    1. I have a 2000 Silverado 4.3wd and it does the exact same thing.. I haven’t figured out what it is exactly either but I now have antifreeze running out as quickly as I can pour it in.. It’s running out of the front center to slightly left side bottom portion of the engine (standing in front of truck facing engine).. Not sure if it’s the water pump, hoses, freeze plug, intake manifold or a combination of the above mentions of possible issues.. But I had the cruising speed (hard jerk/sluggish acceleration) for a few months then suddenly the low coolant light comes on and I pull over and all the antifreeze is on the ground.. so I’m not sure if the issue/issues that caused the antifreeze to suddenly leak was causing the cruising speed (hard shift/sluggish acceleration) because of maybe losing vacuum from a bad hose or gasket.. Or if the coolant lines running to the trans was being affected from the lack of coolant flow and or vacuum loss making.. I’m a trying to troubleshoot everything and I’ll post what I find ASAP

  37. I have a 1994 S-10 with the 4.3 and its been the best truck I’ve owned. I have had it for 11 years and drove it hard the whole time. I owned a pool business for 5 years and always had it loaded down, now an electrician and still using it everyday. Never has left me stranded and besides normal ware and tare with 256,000 its still runs strong today. No Leaks, transmission was replace because of the abuse from overloading it for those 5 years but was expected. Love this truck and see it running well over 300,000.

    1. I have 3 of these. 1) 94 S10 ZR2 pickup – 250,000 mi bought new 2) 04 ZR2 Blazer – 190,000 mi bought at 1yr old 3) S10 2 dr Blazer – 200,000 mi. All have the 4.3. They all just keep going! I will never buy anything else and certainly nothing newer..

  38. 1998 Chevy 4.3 be driving down road and just quits, sometimes it start Right back and sometimes it want, changed lost of parts,still same problem just never know when going happen.

      1. Mine was doing that when the distributor was bad. See if you can pull up on the shaft after pulling the cap? Mine came all the way out so be careful.

  39. 2006 Silverado 4.3 – 2WD – Made in Mexico bought used 20K miles, standard cab 8 foot bed, manual windows & door locks, cloth seats, vinyl floor mats, original rear DRUM brakes. Replaced OEM front rotors w/ aftermarket thicker vented rotors @ 100k miles. Replaced heater fan control temp module inside box 3 times; I don’t run it on 4 or 5 fan position, problem solved. 1st tune up at 100K miles. Oil changes every 4K miles.
    180k+ miles engine now losing coolant but no visible steam, leaks or puddles; Engine now rough idling, suspect head gasket issue. Any ideas ? Also where to buy new or ReMan fuel injection pod & oil pan seals; new radiator hoses. Seattle area dealers all out of stock.

  40. My buddy has a 2002 Chevy S10 with a 4.3 vortec engine. His issue is when driving 2200RPMs and powering on an upgrade the CEL will come on and the miss can be felt, then the CEL will go off. He did some research online and found that someone said his spider injector was bad. I replaced the Spider injector for him and everything seemed fine. We took the truck on a road-test and low and behold the CEL came on when we were at 2200RPMs on an upgrade, read the code and was P0304 like usual. He let the engine cool and removed the spark plugs and cleaned them all and reinstalled. He said he took the truck on another road test and it seemed to run like crap but when he returned back home it cleared up as he pulled in the driveway. Now I’m baffled! Any help will be greatly appreciated.

    1. John – have you checked the coil packs? If plugs are good and injectors are good then I would suspect maybe a bad coil pack. Also possible it is the ignition control module or crank position sensor.

  41. I have a 2002 Chevrolet Silverado 1500 2wd with the 4.3 Vortec I bought new. I’ve driven it daily for over 20-years as my ‘work-truck’. And it’s most definitely been driven like a truck…pulling trailers, hauling loads in the bed, driving on unpaved and even undeveloped land. It still starts every morning and runs like new despite now having over 325,000 miles. I replaced the transmission 2-years ago and the factory water-pump last year. It’s developed a small rear-seal leak that drips about a quart every 3,000 miles…or oil change. Other than that it’s still original and runs like champ.

    Chevy Trucks…like a rock.

  42. I have a 93 Cheyenne and a 99 Silverado both 4.3 the 93 has 365,286 miles on it. Burns a little oil but gets better mileage than my 99 which I’ve replaced distributor to an aluminum after oem failed and upgraded to MPFI injection @ 250k and added a plug and play tune. it now has 350k + on it and is my daily driver with a 120 mile round trip.. has anyone tuned or put larger injectors or headers on one with any noticeable increase in performance?

  43. 1994 S10 BLAZER, L-35 W ENGINE, with the big aluminum, tuned port style intake and central port fuel injection. Over 300,000 miles, runs great, no leaks, uses no oil between changes. It’s had a few repairs, an injector spider, a fuel pressure regulator, and a seeping head gasket once, but it’s been a great truck. Got it painted last year. looks better than new and I’ve been driving it for 19 years, not gonna stop now. It’s a great little engine. strongest factory 4.3 (except the Syclone/Typhoon 4.3).

  44. Have a 2005 Chevy Silverado 1500 with the 4.3l v6 some days it will crank idle fine till I hit the gas then it almost dies if I Pat the gas it will back fire but I’ve replaced distributor, ignition coil cranshaft position sensor cleaned dirt oil off ground need help bad

    1. Sounds like a fueling problem to me – engine isn’t getting enough fuel at RPMs above idle. Try fuel filter and fuel pump.

  45. I bought a 2000 GMC jimmy with this engine. 252000km, had a misfire but threw no codes other than evap P0452 prior owner said it was rattily but disappeared at highway speed. Replaced plugs ended up that #6 was worn to point it did no good. all others almost ready to stop working. after the change all was good before parked for winter and now getting it ready to take my drives test i got an P0301 cylinder 1 misfire. wondering where to start. has new plugs with only 5km max since change.

  46. I have a 2003 GMC Sierra and I must say it is the best vehicle I have ever owned. I bought it new in 2003 for $15,600.00, it now has 188,000 miles and is still running strong. The worst failure I had was the leaking intake manifold gasket.
    Very happy customer.

  47. I have a 2003 S10 4.3 v6. It runs smoothh and strong from a stop but once in overdrive about 55-60 mph it will misfire or stutter, when under load. Otherwise runs nicely. Changed plugs, wires, cap and rotor, still does it. Also cleaned MAF sensor. Getting codes PO155 and 300. Can the oxygen sensor cause this?? Truck has 171,000 miles and sensor is likely original. Thanks!

  48. I had a 1998 Chevrolet WT-C-1500 with a 4.3 vortec engine never once had a problem with the engine running smooth or never misfire but had a lot of other stuff that kept it in the shop!

  49. When I crank my 03 gmc sonoma it’s like the accelerator pedal is to the floor. Can you guess what might cause this?

  50. I have a 2015 Silverado with 4.3 V-6. at about 100k it started with the misfiring. i changed plugs, wires, and coils. it idles really rough about 500 RPMs, but when you get going up over about 1000-1250 it really smooths out. any suggestions?

  51. 2006 Chevy Silverado 4.3l 2wd 5speed. Having some problems with rmp revving up close to 3k when coming to a stop and putting the truck in neutral. They will go down after a few seconds, sometimes it doesn’t but not all the time. Drive it today and it was doing more. I replaced the idle air control valve and no changes. Any suggestions? Thank you.

  52. I have 2001 blazer 4.3 vortex 138000 miles,has usual problems.new intake gaskets injectors distributor and fuel pump ,still misfires obd reads downstream o2 no data only 1 fuse for 3 o2s.I have read o2 s and maf ground directly to ecm and this is sometimes this is the problem ,bad internal terminal .ecm starting to fail but not throwing code yet sometimes they just stop starting ?probably my next trial and error.

  53. Hello every one! I sure hope some one can help with my 4.3 V-6 ???? 1987 GMC 1/2 ton 1500 Sierra. It has 106,000 miles. I bought it from a friend. All ways dependable! A few years ago I drove across town. Leaving, truck wouldnt start. I shot starting fluid in it and it started. This went on for a while. Later on when I drove it for about 30 miles or so. It would die when slowing for a stop. Wouldnt start with the fluid? Had it towed. So far we ( real mechanics) have replaced distributor, Leaving shop I stopped for gas. No start. Then did. New coil, brain box, rebuilt throttle body, new sensors. Same thing, die when coming to a stop. Then changed the EGR valve. That worked for a while. But had to crank several times after it sits. Several weeks ago I drove to a mechanic friends house. Came to a stop sign and it died again. fluid started it. Got to his place shut it off. He was checking it out. Went to start it and no fuel to engine???? But would start with fluid! After it sits for an hour it will start??? Its tuff when it wont do it when you have a tech around!! What am I missing or what else is left??? Great old truck, just cant trust it??? Help Please. Going to Vet reunion in September. Need truck for camping and pulling golf cart. SOS!!!!

  54. Hello again! 1985 GMC Sierra 1/2 ton 4.3 v-6. HELP!! Quits when slowing for stop after about 30 miles. Wont start? Sit for say 1 hour and starts?? You name it I probably changed it? Need Jake or someone to give me a few more ideas please. Only 106,000 miles second owner.

  55. I have a 2007 silverado with the 4.3 litre vortec v6 and I have 296767 miles on this motor and I am just starting to have an issue. In the mornings it spits sputters and runs rough. At lunch you can barely tell its missing. Replaced all the obvious parts. Left me scratching my head on what to do next.

    1. My brother has a 2007 as well and his stopped running. there is a metal plug there that has somethign to do with the fuel pressure that went bad on his. I am trying to find out what the name of that plug is and no seems to know what it’s called. I have a picture of it but cannot find anyone that knows the name of that plug..

  56. I’m not leaving a reply but I’m asking a question I have 1995 Chevy Blazer first truck (SUV) everyone round town calls it a truck anyways got her when she had 130k minor details subs, paint grill, make her look purrty I’m the second owner an ole gentleman had it in WV before me and she made her way down in her in TN somehow and some way anyways it’s gotta 183k on her got 17in American bullet hole rims and 2.5in lift for her and now the trans slipping my question is 183k with the engine running like a dream cranks every turn has a little spurting problem when I’m coming to stop here and there but my question is it worth to fix the transmission? Do I wanna fix it personally yes I have had dreams of the rims and that lift on my ole lady she has gotten me through thick and thin but at the same time I don’t know if I should that’s why I’m asking y’all I’m 23 now still living at home with momma I know the 4.3 are strong if I keep changing the oil and sparks all I have done so far is everything fuel related is literally brand spanking new fuel lines, fuel pump and filter, spider injector all the main stuff y’all know 😂 but legit that’s my question should I get a new transmission for her?

    1. Hi Zach,

      That’s a challenging question for any outsider to answer. Based on your comment it sounds like you really love your 95 Blazer and 4.3 Vortec. If that’s the case then it’s likely worth fixing the transmission and keeping. It’s certainly cheaper than a loan in the long-run. However, 25+ year old trucks (SUV’s) do take some extra TLC and there’s a simplicity to owning a newer vehicle.

      Ultimately, if you’re willing to deal with the occasional challenges of an older vehicle then it probably makes sense to keep the Blazer (especially considering you seem to love and enjoy it).

      Regards,
      Jake

    2. Hi Zach. I have now owned three. A 92″ blazer a 99″ blazer and currently a 2001 Jimmy which is the same thing as a Blazer by another name. I got the Jimmy in 2017 and have had to do lots of repairs. It is becoming a hobby with me. At 157000 I had the 4L60E tranny rebuilt. It now has 199000 on the Jimmy. I do ball joints, spider injectors, rebuild AC system and so on. Being that I live in central NY near Syracuse, I do body work too. Rust belt. Keep on trucking. There are some differences in that 1995 you have in the engine. No balance shaft for one. Your ignition still has points I think. My jimmy has an ICM instead of mechanical points. Consider upgrading to a newer model if you can. I got lots of miles out of my 92″ though. The 99″ was my spirit animal. I drove that vehicle for 14 years and 403000 miles.

  57. Have an ‘05 Silverado 4.3 manual transmission regular cab. Started acting up about 2 1/2 months ago. Doggy and no power, somewhat rough idle, reduced fuel economy. Codes 0172 (fuel mixture too rich) 0300 (random engine misfiring) 0101 (mass air flow sensor)
    So far have replaced the spark plugs, plug wires, coil and ignition module, distributor, cap and rotor, upstream oxygen sensor, mass air flow sensor, and air filter.
    None of these have made a nickel’s difference. It’s still doggy and throws the same codes. Occasionally the check engine light will flash for 30 – 40 seconds during a slight work load.
    The issue appears less when the engine is cold or the ambient air temperature drops to around 60 or less.

  58. My 1992 s10 blazer with a 4.3 vortec fuel injected four speed automatic trans. Starts right up with cold engine when engine gets up to running temp and I turn it off it won’t start until engine gets cold am told it could be eprom which I just can’t find is there anything else that could make car not start once it gets to running heat

      1. What we did find was the catalytic converter on bank 1 (driver’s side) was closed to being plugged. Once that was corrected, it’s like a new vehicle.

  59. Had those same issues and replaced most of the same things. It ended up being the catalytic converter for bank 1 (drivers side). It was badly restricted and needed replacing.

  60. will the 97chevy c1500 4.3 v6 vortec motor interchange with 95 chevy c1500 also 4.3 v6 vortec motor

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