The 6.6L LMM replaced the LBZ Duramax midway through 2007 due to emissions regulations. One of the big changes to the LMM was the addition of a diesel particulate filter, or DPF system. Alongside the DPF is regeneration cycles that occur to clean the particulate filter and system.
While the LMM is actually a very reliable engine, one of its most common problems is DPF failure. This was a completely new emissions system that hadn’t been used on any Duramax engines before so it’s no surprise it had a few problems with it. The regeneration cycles on the DPF system require highway driving to allow the exhaust to get hot enough to burn all of the trapped particulates it captures. LMM engines suffer from excessive regeneration when the exhaust doesn’t get hot enough which leads to failure of the DPF and clogging issues which can then lead to problems with the fueling and cooling systems.
Ultimately, diesel particulate filters are good for the environment but not so good for both performance and reliability. Therefore, deleting the LMM DPF system is a common choice. This guide is going to cover the LMM emissions systems, the benefits and downsides of deleting the DPF, and mention a few of the best delete kits on the market.
What is the DPF System?
The DPF, or diesel particulate filter, as the name suggests is a filter to capture diesel particulates. Diesel fuel doesn’t burn as cleanly as normal gasoline which results in small chemical particles forming within the exhaust gas. These particles are known as diesel particulates and commonly referred to as diesel soot.
The particulate filter is responsible for capturing these harmful particles and then burning them through “regeneration” cycles. Once the filter collects a certain amount of soot it has to be burned off otherwise the filter will clog. This is where regeneration cycles come in. During a regeneration cycle diesel fuel is injected into the exhaust stream to heat the DPF to over 1,000 degrees which burns all the soot out. Since this process uses fuel it also results in worse gas mileage.
Other LMM Emissions Systems
The DPF isn’t the only emissions system on the LMM. Diesel exhaust systems also have a diesel oxidation catalyst, or DOC, which is essentially the equivalent of a catalytic converter on a gas engine. The DOC sits after the downpipe and before the DPF within the exhaust system.
Fortunately the LMM doesn’t have the SCR system like the LML. Therefore, the exhaust in the LMM goes as follows: downpipe > DOC > DPF > cat-back piping and muffler.
Additionally, the LMM has an EGR system, or exhaust gas recirculation. This emissions system is separate of the exhaust-related emissions equipment and instead occurs before the exhaust. EGR systems recirculate exhaust gases back into the engine before they reach the exhaust tract which allows the gases to be re-burned through the combustion cycle therefore resulting in cleaner exhaust gases.
What Does an LMM DPF Delete Remove?
Deleting the LMM DPF actually deletes more than just the diesel particulate filter. In addition to the DPF it will also eliminate the diesel oxidation catalyst too. The DOC and DPF actually sit in two different pipes so they can be deleted or removed separately, but all the delete kits on the market will remove both of them. If you are going to delete one it makes sense to maximize the benefit and remove the other.
An LMM DPF delete is essentially just an upgraded exhaust system that doesn’t have these filters. It bolts to the downpipe and to the cat-back portion of the exhaust system and therefore deletes all of the emissions systems that sit within the exhaust.
Ultimately, it deletes:
- Diesel particulate filter (DPF)
- Diesel oxidation catalyst (DOC)
- O2 sensors attached to the exhaust
- Regeneration cycles (no equipment, just the process)
What about the EGR System?
The EGR system sits before the exhaust and therefore is not deleted alongside the DPF. Deleting the EGR will require a separate delete kit and is a bit more complex since it isn’t just a piece of piping like the exhaust system is. It includes a number of valves and hoses that will need to be swapped out in order to block out the system.
Duramax LMM DPF Delete Benefits
Deleting the LMM DPF is about performance, reliability, and gas mileage. As mentioned, the DPF system frequently clogs and fails which requires a replacement. New DPF’s are $1,500+ (the OEM one is like $3,000) so deleting it replaces the possibility of an expensive future repair. A clogged system can also result in other problems and require additional repairs.
With respect to performance, both the DPF and DOC create a lot of backpressure in the exhaust system which restricts performance and negatively impacts the turbo. Lastly, since the regeneration cycles use fuel to burn the , it results in worse fuel economy.
LMM DPF Delete Pro’s:
- Power gains in excess of 100hp (gains mostly come from the tune itself)
- 2-4mpg improvement
- Increased turbo efficiency and reliability
- Reduced exhaust backpressure
- Lower EGTs
- Increased reliability
- No regen cycles
Power gains predominantly come from tuning. A stock LMM with a deleted DPF won’t necessary lead to big power gains – the gains are more so with respect to power potential. Henceforth, gains mostly come from the tune and the benefit of the delete increases the further you push the LMM mod wise. Deleting it reduces exhaust backpressure which impacts efficiency and power produced by the turbo.
Outside of power gains, you will get the benefit of improved gas mileage and increased performance. While the biggest problem it creates is failure of the DPF itself, running on a clogged filter can lead to other issues if not addressed properly, such as turbo failure as it increases backpressure in the exhaust which puts excess stress on the turbo. Additionally, it creates lower EGTs which is beneficial for block and internals especially on LMM’s that tow a lot.
However, the biggest benefit is probably the increased gas mileage. A delete, tune, and intake can give you up to around 5mpg improvements which is meaningful if you drive a lot.
LMM DPF Delete Con’s
While the benefits seem like a no-brainer there are some considerations to take into account before deleting your Duramax.
- EPA concerns / it is illegal and will fail emissions
- Reduced resale value
- Difficulty finding shops to work on your truck
- Install and certain repairs will need to be DIY’d
- Bad for the environment
- Requires a tuner
Deleting emissions equipment is illegal and can get you in trouble with the EPA or with the state. Certain states like California will send your deleted truck straight to a crusher if it is caught. A recent increase in focus on deleted trucks makes it difficult to resell or get work done on it from the dealership or repair shops. Since these are older engines warranty likely isn’t a concern, but you will still have to find a way to skirt emissions testing since it will fail.
The last point is that a delete is also a bit more expensive because you need a kit + a tuner, which is close to $1,000 for the tuner alone. Ultimately, deleting the DPF costs just as much as replacing it does.
Should You Delete the LMM DPF System?
It makes sense for gas mileage, reliability, and high horsepower builds. However, dealing with a deleted truck might outweigh these benefits.
Adding a tune and some bolt-on mods can give really good and legal power gains on the LMM. Unless you are upgrading the turbo and shooting for aggressive power levels then there isn’t really much of a performance justification for a delete. The stock turbo can handle 550whp but the transmission can only have about 500whp so getting to a point where it makes sense to delete the DPF is going to put you $10k+ in mods first.
With respect to reliability – so long as you don’t drive around with a clogged DPF for too long the biggest cost is having to replace the system. But, a new aftermarket DPF is the same cost as deleting the factory one. Deleting it after it has failed is the same as doing it before, so that is one option here. Lower EGTs and engine temps are beneficial for long-term reliability and longevity.
Lastly, it is a headache to own an illegal vehicle with respect to inspections, registration, resale, and general maintenance.
Ultimately, we really don’t recommend a delete unless you are chasing crazy power, the existing DPF has already failed, or if, in your opinion, the fuel economy gains will outweigh the cost and headache of owning a deleted truck.
How to Delete the 6.6L LMM DPF
While we don’t recommend it, here are the two components you will need to delete the particulate filter and oxidation catalyst:
- LMM DPF Delete Kit
- Tuner with delete tunes
The delete kit is essentially just a portion of the exhaust system, or a full exhaust system. The most common route (and most kits on the market) are a full 4″ exhaust system that goes from the downpipe-back. Next, you’ll need a tuner that has delete tunes on it. Since most tuners won’t do custom delete tunes anymore for liability reasons, you will need to buy a tuner with pre-loaded delete tunes on it, or buy the files to load onto your existing tuner.
1) DPF Delete Kit
The DPF and DOC sit between the downpipe and the muffler. Therefore, this is the only section of the exhaust that actually needs to be replaced. However, all the kits available online include a full downpipe-back exhaust system which replaces the whole exhaust minus the downpipe. This will result in the best power gains and the larger 4″ exhaust will reduce backpressure more than just replacing the middle section and leaving the factory muffler. The alternative is to custom cut and weld the portion needed in if you want to keep the factory muffler.
Best Delete Kit: Diesel Dudes LMM 4″ Downpipe-Back Kit
Diesel Dudes is one of the only brands available on the market with an LMM delete kit. Their kit is a full 4″ downpipe back exhaust system made of stainless steel. It bolts directly up to the stock downpipe and is an easy DIY install. It is a straight-pipe design so it will add a decent bit of sound to your truck.
Buy Here: Diesel Dudes LMM DPF Delete Kit
2) DPF Delete Tuner
Tuning is a must with a DPF delete. Without a tuner your truck will still try to perform regeneration cycles which will lead to the engine going into limp mode and pretty much being undriveable. Therefore, a tuner is needed to code out regen cycles and to eliminate check engine lights from the absence of the O2 sensors and such.
Since custom tuners won’t do deleted any more your best bet is to buy a tuner that comes pre-loaded with a delete tune. The best tuners on the market for this are the EFI Live and the H&S Mini Maxx. Additionally, if you have an existing tuner you can buy a tune and download it into your existing hardware. Since neither of these companies sell their tuners with delete tunes on them anymore you will need to buy them third-party, like from Diesel Dudes, to get the delete tunes.
We recommend buying them here to get them with the delete tunes:
Duramax LMM DPF Delete Summary
The LMM was released after the LBZ and included a new emissions system: the diesel particulate filter. In addition to the DPF, the LMM also has a DOC system which is like a catalytic converter. Additionally, it has an EGR system which sits outside the exhaust system.
DPF filters are prone to clogging and failing on the LMM which can lead to some costly repair bills. Therefore, deleting the system is a common reliability item as it lower EGTs and reduces engine heat and stress on the turbo which is all beneficial for longevity and reliability. Additionally, the DPF system uses fuel to burn the particulates it captures, which has a negative impact on gas mileage. Furthermore, the DPF and DOC are both bad for performance and power potential as they create backpressure buildup and restrict exhaust flow.
Deleting the DPF is common for better gas mileage, more reliability, and better power gains. However, there are a number of downsides such as the illegality in doing so which can create possible legal issues with the EPA and regulators. Additionally, it reduces resale value, makes repair work more challenging, and creates a hassle with respect to registration and emissions testing.
A delete kit and delete-loaded tuner are the two things required to delete the DPF on the LMM. Delete kits run about $700 with tuners costing about $1,000. Ultimately, it costs about $1,700 in parts to delete the DPF which is also the same cost as a new aftermarket DPF system.