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Diesel Tech Q&A: 2011-2016 Duramax Fuel Concerns

Originally Published in Trailer Life Magazine

2011-2016 Duramax Fuel Concerns

Red letter QI have a 2015 6.6-liter Duramax and have heard about there being a problem with the injection pumps as the mileage nears the 100,000-mile mark. What do I need to know about this, if it is an issue?
James Beagle

Red letter QI have a 2016 Silverado with a Duramax engine and 24,000 miles on the truck. My question is in regard to the fuel filter. The truck is used only to pull my travel trailer, and it is stored in a heated garage during the winter. How often should I change the fuel filter? The driver information center (DIC) tells me the filter’s life is at 50 percent now. Simple math tells me the filter will not be due to be changed for another four years. Do I go with what the DIC tells me, or should the filter be changed more often?
Dave Beyer

Green letter AA little background about the 2011 to 2016 Duramax fuel system, specifically the CP4 (CP4.2) high-pressure fuel-injection pump issues. Since its introduction in the LML/LPG Duramax in 2011, owners have experienced sudden catastrophic failures that require complete replacement of the injection system from fuel tank to injectors. It’s about a $10,000 repair.

Many of the failures occurred during the vehicles’ warranty period, so no one outside of GM knows how many vehicles were affected. Some failed with less than 100 miles, others with more than 100,000 miles. But there were enough failures that the automotive aftermarket began offering CP4-to-CP3 “conversion kits” and “disaster-prevention kits” early on to get rid of the newer-style pump and replace it with the older, more reliable CP3, or redirecting return fuel to prevent the debris from failure circulating through the entire Duramax fuel system.

GM issued a technical bulletin (PIP4949D) in August 2014 discussing diagnostics and repair for the CP4.2 failure. There were enough complaints about failures that a class-action lawsuit was filed by GM vehicle owners in December 2018, and it continues today.

See Related Story: Diesel Heart Transplant: Duramax CP3 Swap

According to the lawsuit filed by Morgan & Morgan Business Trial Group against GM and Bosch, its clients’ pickups and SUVs have diesel engines with the CP4.2 fuel-injection pumps that suffered catastrophic failures, costing the owner of each vehicle from $5,000 to $10,000 in repair costs. Among those are owners of 2011 to 2016 GMs with the 6.6-liter Duramax LML/LPG diesel V-8. (In 2017, with the debut of the LP5 Duramax, GM switched from the Bosch diesel fuel-injection system to Denso.)

The Bosch diesel injection-pump experts I spoke with say the CP4.2 problem arises from not having enough lubrication in ultra-low-sulfur diesel (ULSD) fuel, which is what we have at the pumps. Sulfur is the primary lubricant in diesel. When there’s not enough lubricity in the fuel, the CP4.2’s “crankshaft” and the plungers that do the compressing of the fuel heading to the injectors start shedding metal. The time from the start of this wear to complete failure can be mere seconds. It can happen at any time from zero miles to several hundred-thousand miles. There’s no definitive mileage or time frame to say if or when the pump will fail.

Engineers familiar with the intricate inner workings of the Bosch CP4.2 injection pump advise regularly using a diesel-fuel additive that imparts more lubricity in the fuel. But as the GM tech bulletin says, “Using a commercially available diesel-fuel additive can be helpful but cannot be guaranteed to prevent CP4 pump failure.” The extra lubricity will extend the pump’s life but is not a guarantee against failure.

GM service techs warn that if you’re experiencing a hard start or no start, or are getting the following trouble codes — P0087, P0088, P0191 or P128E — a pump failure could be the problem. Another aspect of this CP4.2 injection-pump issue is the pump is extremely sensitive to water or fuel contamination of any type, air in the fuel, and running out of fuel. Any one of those situations can cause CP4.2 pump failure.

It’s wise to change the fuel filter regularly (even before the DIC says), make sure that the fuel system is bled of any air before startup, and invest in an aftermarket lift-pump/filter system such as those offered by FASS Diesel Fuel Systems and AirDog Lift Pumps.

As a side note, the Bosch CP4.2 high-pressure fuel-injection pump is also used in 2011 to present Ford 6.7-liter Power Strokes and 2014 and newer 3.0-liter Ram and Jeep EcoDiesels. There have been reports of CP4 failures in those engines as well, but they are not as problematic, apparently, as the Duramax.

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Bruce W. SmithA respected automotive and RV journalist and longtime Trailer Life contributor, Bruce W. Smith has held numerous editorial titles at automotive and boating magazines, and authored more than 1,000 articles, from tech to trailering. He considers his home state of Oregon a paradise for RVing and outdoor adventure.

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