The Duramax L5P is GM’s latest diesel in the 6.6L Duramax family. This means it is also loaded with every single diesel emissions system you can imagine. The L5P has selective cat reduction, diesel exhaust fluid, diesel particulate filter, diesel oxidation cat, and exhaust gas recirculation.
While these emissions systems are great for reducing emissions, they do come with a handful of downsides. The L5P doesn’t have a whole lot of common problems with its emissions systems, but they are very expensive to replace when they do break. Any DPF system is prone to clogging and replacing it can easily cost in excess of $5k. Additionally, they are restrictive from a performance perspective.
Deleting the L5P DPF system is common for both preventative maintenance and performance reasons. Not having all these complicated systems reduces potentially expensive repairs, and also allows for more power production. This guide is going to discuss the L5P emissions systems, the benefits and downsides of deleting the DPF system, and how-to delete the L5P DPF system.
What is the Duramax L5P DPF System?
A DPF is a diesel particulate filter. When diesel engines burn fuel they produce “particulates” along with the exhaust gases. Diesel particulates are small chemical particles that are bad for the environment and human health when inhaled. The DPF sits within the exhaust system and captures these particulates in the exhaust gases. It then burns them down via regeneration cycles.
As we mention in our intro paragraph, the L5P also has SCR, DOC, DEF, and EGR systems as well. The DPF system is actually the last emissions system in the L5P exhaust. First is the diesel oxidation catalyst which is similar to a traditional catalytic converter. This sits right after the downpipe in the exhaust system. After the DOC is the SCR system which uses DEF fluid to break nitrous oxide down. These two systems sit before the DPF to burn exhaust gases down as much as possible before getting to the particulate filter.
Similar to the LML, the L5P SCR and DPF system are actually integrated into the same piping in the exhaust. The exhaust system therefore looks like this: downpipe > DOC > SCR & DPF > cat-back and muffler.
One other emissions system we mentioned is EGR, or exhaust gas recirculation. This is actually the first emissions system, but it doesn’t sit within the exhaust. EGR captures exhaust gases before they reach the exhaust system and recirculates it back into the engine so the gases are re-burned through the combustion process.
What Does an L5P DPF Delete Kit Remove?
Calling it a DPF delete is slightly confusing since an L5P DPF delete actually removes more than the DPF system. Deleting the DPF will also delete the DOC, SCR, and DPF system. Because the SCR system is deleted, you will no longer need DEF fluid either, so that is technically deleted too.
Removing the L5P DPF will delete:
- Diesel oxidation catalytic (DOC – this is it’s own pipe in the exhaust)
- Selective cat reduction (SCR)
- Diesel exhaust fluid (DEF, used in conjunction with SCR)
- Diesel particulate filter (DPF)
So, it ultimately removes every emissions system with the exception of the EGR since this isn’t within the exhaust. A DPF delete kit is just one piece of exhaust piping that bolts up to the downpipe and to the muffler, therefore deleting every emissions system in the exhaust.
Deleting the L5P EGR
A lot of times when people talk about deleting their trucks, you’ll hear about DPF and EGR deletes. These are separate deletes. Deleting the L5P DPF does not delete the EGR system.
Deleting the EGR system is slightly more complicated as it requires blocking the EGR valve and plugging a number of hoses. Installing an EGR delete is a lot more complex (but not that difficult) compared to the DPF, since a DPF delete is literally just one piece of exhaust piping that bolts up directly.
The EGR system also has an EGR cooler which cools down the exhaust air before it’s dumped back into the intake manifold. The EGR system isn’t as restrictive from a performance perspective. Therefore, it’s primarily removed to prevent failure of the EGR cooler which is common and costs a couple grand.
Dumping exhaust gases back into your intake system and combustion chamber also sends diesel particulates and diesel soot back into the engine. This generally isn’t good for reliability and engine longevity so the EGR is mostly deleted for preventative maintenance and reliability purposes.
Duramax L5P DPF Delete Pro’s
The two reasons for deleting the DPF are reliability and performance. DPFs clog easily and are expensive to repair. SCR can also fail and requires DEF fluid which is an annoyance and also reduces gas mileage. And from a performance perspective, all these filters create a lot of backpressure in the exhaust system which is bad for turbo efficiency, restricting performance.
L5P DPF Delete Pro’s:
- Power gains in excess of 100whp when turned (gains mostly come from tune)
- Gas mileage improvements from 2-5mpg
- Increased turbo efficiency and reliability
- Decreased exhaust gas temps
- Reduced backpressure in exhaust system
- No more DEF fluid or regen cycles
- Improved reliability, decreased maintenance costs
The one caveat to power gains from a DPF delete is that it really only matters if you are pushing the L5P to the extreme. The L5P can push over 800whp easily with the DPF system still installed, so there really isn’t a need to remove it for performance reasons. There is a point to be made if you are upgrading your turbo, but if you’re just dropping bolt-ons on the L5P you don’t need a delete for performance.
If you aren’t chasing insane power, the only reason for removing emissions systems is for reliability. It will reduce potential maintenance and repair expenses and result in a healthier engine and turbo via less backpressure and lower EGTs. Additionally, you’ll save some money on diesel fuel and DEF fluid.
6.6L L5P DPF Delete Con’s
With great benefits also comes great downsides. Deleting emissions systems isn’t a decision to make or take lightly. There are a lot of compelling cases for leaving your GM truck in tact, such as:
- Decreased resale value
- Warranty is lost
- Dealer won’t touch your truck
- It’s technically illegal and can come with big fines
- Will fail emissions testing
- Installs must be DIY’d (shops won’t install these anymore)
- Harmful for the environment
- Needs to be used in conjunction with a DPF capable tuner
You might not care about the impact to the environment. If that’s the case the biggest reason not to do it is the hassle of dealing with an illegal truck. Dealers, and a lot of shops nowadays won’t touch deleted trucks due to EPA crackdowns and they certainly won’t install deletes for you. Warranty is out the window, if you still have any. Resale value drops since registering and emissions testing a deleted truck is a challenge.
And in addition to buying a delete kit, you’ll also need to buy a tuner capable of handling a deleted L5P. They don’t make these off the shelf anymore so you’ll need to track down a used one or find a tuner who has the balls to custom tune a DPF delete for you. All in all, it’s getting a lot more difficult to find shops, tuners, etc. to help since the EPA is fining these people heavily if they get caught.
Should You Delete Your DPF System?
Added power, improved reliability, and less money spent on fuel sounds like a win-win. However, the hassle of having an illegal truck can potentially outweigh the benefits of doing so. We really don’t think you need to do it for performance. It really only restricts performance when you are pushing the envelope, which you aren’t doing with bolt-on mods. Which means it comes down to whether or not you should do it for reliability purposes.
We really don’t recommend deleting the DPF unless you are one of the few power chasers, or your DPF, SCR, DOC has already failed. Deleting it after it fails is just as easy as deleting it now. So we recommend doing it as a last resort when your existing system has failed and you’re stuck with a $5k+ repair bill that you can’t afford.
If your emissions systems are good and your power goals are modest, keeping your DPF system is probably the best route to go. Contrary to what you’ll read on some forums, these systems aren’t death machines that are killing L5P’s left and right. These engines are pretty reliable and there isn’t any data yet suggesting that the DPF or EGR are drastically impacting reliability or longevity.
How to Delete Duramax L5P DPF System
If you don’t care about anything we’ve said so far and want to delete your DPF system, here’s how it’s done. You’ll need two things:
- L5P DPF Delete Kit
- Tuner with DPF-delete capabilities
The delete kit is simply a piece of exhaust piping that bolts to the downpipe and muffler. You have a few options here like just replacing the DPF/DOC section of the exhaust, or opting for a full downpipe-back exhaust system. The second component is a tuner. Most tuners no longer have built in DPF delete capabilities, so you’ll need a custom tune or a used tuner.
1) L5P DPF Delete Kit
Every emissions component sits between the downpipe and the muffler. A simple delete kit is pretty affordable and just has a single exhaust pipe that goes from the downpipe to the muffler. It usually is a direct bolt-on without any modifications needed, but it can very depending on whether you have a long bed, short bed, etc. Most kits are $300-$400. Alternatively you could try to get a chop shop to cut this part of the exhaust out and weld a straight pipe in.
Option two is to upgrade the whole downpipe-back exhaust system. You have a lot more options here. You can go with a 4″ or 5″ exhaust piping, you can keep the muffler or do a muffler-delete, and so on. Ultimately, this comes down to whether you want a louder exhaust system or not. Depending on what you choose and whether you want stainless steel or aluminum, this option ranges from $500-$1,000+.
If you just want an easy delete, just get the delete pipe. If you want a full exhaust system you can opt for the more expensive downpipe-back kit. And if you want to go further, you can also upgrade the downpipe for another ~$200 for even less restriction and backpressure.
2) DPF Delete Tuner
Tuners used to have built-in DPF delete tunes, until they started getting in trouble for this. One case is H&S who made the Mini Maxx which was one of the best delete tuners. H&S went out of business after a massive fine they received for selling emissions-altering devices. So, now finding a new handheld tuner with this capability is unlikely.
All of these emissions systems have various sensors and such. If you don’t tune these out, tune out regeneration cycles, and all that jazz you’ll end up with an undriveable truck.
So, your options are either custom tuning or buying a used tuner like the H&S Mini Maxx. You might be able to find some tunes available for sale on the internet that you can download into something like the SCT X4, but again, it’s becoming challenging to find anyone who is willing to do this.
6.6L Duramax L5P DPF Delete Summary
There are four primary emissions systems on the L5P. EGR, DOC, SCR, and DPF. All of these systems with the exception of EGR sit within the exhaust system. Deleting the L5P DPF will remove not only the DPF but also the DOC and SCR components, and the need for DEF fluid. The EGR must be deleted separately.
All of these emissions systems are prone to clogging and failure. And replacing them costs thousands of dollars. Therefore, deleting these emissions components is popular for preventative maintenance, repair, and reliability purposes. Additionally, there is a performance rationale as these filters create backpressure and restrict exhaust gas flow which is bad for EGTs and the turbo.
You end up with a healthier and more reliable L5P once the DPF and other components are gone. Also, while it doesn’t really create a ton of power, it creates a lot more power potential for those pushing the limits. On the downside, deleting the DPF is illegal and is a hassle in terms of warranty, repairs, inspections, resale, etc.
The two things required are a DPF delete kit and a tuner. The delete kits run from a few hundred bucks to $1k+ depending on whether or not you want to replace the whole system. Tuners and a custom tune can run you another $1,000 as well. So, deleting the DPF on an L5P costs about $800 to $2,000 depending on how you do it.