How to Prevent The Dreaded LML CP4 Injection Pump Failure

With everything going on in the news today regarding the on-going lawsuits with General Motors (GM) in the United States we have seen a massive spike in phone calls, emails, and messages regarding the lawsuit from customers on how this will affect them in Canada and what is going on with these LML CP4 Lawsuits.

The LML was first introduced in 2011 phasing out the previous LMM platform and continued its run until the end of 2016 when it was replaced with the 2017 L5P Duramax. These LML trucks were fitted with the dreaded Bosch CP4 that has been an issue from day one of production with the LML trucks. 

These pumps have been the cause of an enormous lawsuit laid upon General Motors for the number of failures these pumps have caused. They claim these pumps weren't designed for the North American diesel we use today, and at this time there has been no outcome of this lawsuit, so it's going to fall on the driver to repair this issue if it ever arises. If you own one of these trucks, most likely you’re out of warranty by this point, or you’re getting close. So we would like to go over what the options are to prevent this from happening to you.

What Happens

The OEM Bosch CP4 pump that comes in your LML from the factory has a tendency to fail spectacularly, according to the recent lawsuit, these pumps began failing the day the first drop of diesel fuel landed in their tanks. There is a lot of speculation found online these days regarding why they’re failing, whether they’re failing because of the quality of fuel, maintenance, or simply luck of the draw. We’d prefer to not speculate and point fingers, instead, we’d like to talk about what happens to your pump and fuel system, the steps you can take to prevent the failure, and how you can potentially limit the damage to your fuel system in the event of a CP4 failure. 

The CP4 pump has a tendency to tear itself apart from the inside for lack of technical terms. As it begins to fail, the CP4 starts shedding metal shavings and metal contaminants into the fuel. The high-pressure fuel then leaves the pump and travels through your fuel system towards your injectors. We all know how much injectors love metal going through them at 25,000psi right? It doesn’t take long for the contaminated fuel to start wreaking serious havoc on your injectors as the LML runs a closed-loop system. This means the fuel cycles directly back to your fuel pump without being filtered again, this keeps pushing through your fuel system causing more and more damage. If (or when) this happens to you, it’s not just the pump that needs replacing, it’s your pump, all 8 injectors, fuel regulator, and you will need both fuel rails cleaned. It’s not like we see this happen every day, but when it does, it’s an upset Duramax owner with no choice but to get their truck back on the road. 

Preventive Measures

The best way to prevent this from starting in the first place is to always fuel up at a reputable fuel station and ensure your filter is changed on schedule (with OEM or equivalent). These are incredibly simple steps that can make a big difference over the life of your truck. 


Another step you can take is adding a FASS Fuel System, it’s a fantastic way to ensure your injection pump is getting a healthy supply of the cleanest fuel it can. Duramax trucks rely on the injection pump to suck fuel all the way from the tank, anything you can do that makes its life easier is a good investment. The added filtration benefits and the removal of air bubbles from your fuel is simply an added benefit. 


Exergy Fuel System Saver

If you plan on sticking with your OEM CP4 in your truck or want some peace of mind while you save some cash for a replacement, the Exergy Fuel System Saver is a no brainer. Simply put, the Exergy Fuel System Saver does exactly what you'd think it does. It saves your fuel system in the event of a failure. Your OEM inlet valve has an 80 Micron screen that is known to rip in the event of a CP4 failure, the Exergy piece has Dual 25 Micron that is designed to not only stop all the metal contaminants from getting to your injectors, but it will also plug the fuel supply and choke out your engine to ensure nothing makes it to your injectors and potentially saving you thousands in repairs. 


CP3 Conversion Kit

Ultimately, the only true fix for this is problem is to purchase a retrofit kit and backdate your pump to the trusty CP3! However, this will require the addition of some custom tuning but it will ensure you can trust your truck on those long road trips or on those cold morning startups. The CP3 is a much simpler pump that has been used in GM trucks from 2001-2010 and Cummins engines from 2003-2018. Not only is the CP3 more reliable, but if you're power-hungry, you can upgrade to a 10mm or 12mm striker pump and easily get to that 800hp range on a single pump setup. 


These are the products that we are using in-house, every day to help these trucks stay on the road. It may seem expensive, or something that you don't really want to do, but trust me, even at the extreme end - a CP3 conversion is going to be A LOT cheaper than dealing with a CP4 pump failure. This is really the only downfall we've seen on these newer LML engines, so at the end of the day, it will be worth the cost to maintain a great truck, with tons of power. 

Hopefully, this has shed a little light on this topic for you and if you are in the market or even just thinking about how to prevent a failure, these products have been proven to work.

Questions? Thoughts? Let us know below!