It fails without warning
Most owners get no useful notice. The truck runs fine, then cranks and won't restart — usually far from home, often loaded.
Chevy / GMC 6.6L LML Duramax · 2011–2016
Everyone calls it a downgrade. Your fuel system calls it insurance.
The LML Duramax left the factory with a Bosch CP4.2 high-pressure pump — the same design that has been destroying fuel systems on both sides of the truck market. Converting back to the older Bosch CP3 is the one change that takes the failure off your truck for good. Complete kit, no tuning required, $4,700 installed.
The Problem
When a CP4 lets go, it takes everything downstream with it.
The CP4.2 was never a good match for U.S. diesel fuel lubricity. When the internals start to wear, the pump grinds itself up and pushes metal debris through the entire high-pressure circuit — injectors, rails, lines, and back into the tank. It rarely warns you first. By the time the truck stumbles, the contamination has already spread.
It contaminates everything
Metal from the pump travels through rails, injectors, and lines. Replacing only the pump on a contaminated system buys you a second failure.
It's a five-figure repair
Once every contaminated component is replaced, a post-failure fuel system is a five-figure job — we do the complete contamination kit with the CP3 conversion for $12,000 installed.
The CP3 doesn't do this
The pump GM used before the LML has millions of trouble-free miles behind it. Going back to it is the entire point of the conversion.
The Fix
A complete CP3 conversion — no tuner, no compromises.
We install the complete Fleece Performance CP3 conversion for the 2011–2016 LML. It is designed to bolt in with OEM-style fit and finish and to run on the factory calibration — no tune and no regulator table changes.
- Brand-new Bosch CP3 high-pressure pump
- Molded fuel feed and return hoses for a factory-quality install
- High-flow CP3 fuel fittings
- Valley feed line that supports an aftermarket lift pump later
- No tuning required — the stock calibration stays
- No FCA regulator table changes needed with a stock CP3
- 50-state compliant — CARB EO# D-834-1
- Consistent rail pressure under tow and haul loads
- Fits 2011–2016 Chevy / GMC 2500HD and 3500HD 6.6L LML Duramax
Running a low-pressure lift pump? Feed pressure to the CP3 should stay in the 5–6 psi range with this kit. If you already have a lift pump, tell us the brand and we'll set it up correctly during the install.
Pricing
One number, pump included.
Two paths, depending on where your truck is: convert before the CP4 fails, or replace the system it contaminated and convert at the same time.
Eliminate
LML CP4 to CP3 Conversion
$4,700 installed
- Complete conversion kit including a new Bosch CP3 pump
- Removes the CP4.2 failure point permanently
- No tuning required — factory calibration retained
- Parts, labor, and fluids included
- Fits 2011–2016 6.6L LML Duramax
After A Failure
Contamination Kit with CP3 Conversion
$12,000 installed
- Eight new Bosch common-rail injectors
- Both Bosch fuel rails, left and right
- Complete high-pressure line set and fuel return line assembly
- New fuel injector assembly
- Full Fleece CP3 conversion with a new Bosch CP3 pump
- Also the fix for DEF contamination and water in the fuel
- 50-state compliant — CARB EO# D-834-1
- Fits 2011–2016 6.6L LML Duramax
Conversion pricing reflects parts and labor for the listed fitment on a truck with a healthy fuel system. Contamination kit pricing assumes the failed injectors and pump come back to us as cores — if they can't be returned, core charges apply and we'll say so in writing before we order anything. Final quote may vary by truck condition, existing modifications, and location. Fleet pricing available for multiple units.
Inside The Contamination Kit
What $12,000 actually replaces.
When a CP4 comes apart, metal reaches everything the fuel touches. Replacing the pump alone leaves debris sitting in the rails and injectors, and the new pump eats itself on it — that is why these trucks come back. This kit replaces the contaminated hardware outright and converts the truck to a CP3 in the same job.
| Replaced | Qty | Why it has to go |
|---|---|---|
| Bosch common-rail injectors | 8 | Debris scores the internals and the nozzles never seal correctly again |
| Bosch fuel rails, left and right | 2 | Metal settles in the rails and washes downstream into anything new |
| High-pressure pump-to-rail lines | 2 | Cannot be flushed clean at the pressures these lines carry |
| High-pressure injector lines | 8 | One contaminated line takes out the injector it feeds |
| High-pressure crossover line | 1 | Carries the same debris between banks |
| Fuel return line assembly | 1 | Returns contaminated fuel straight back into the system |
| Fuel injector assembly | 1 | Replaced as part of a complete, correct repair |
| Fleece CP3 conversion with new Bosch CP3 | 1 | Removes the pump that caused the failure in the first place |
Put DEF in the fuel tank? Same repair.
A CP4 grenading is not the only way an LML fuel system gets destroyed. DEF in the diesel tank and water in the fuel do the same kind of damage — they attack every wetted component, and the truck cannot be saved by draining the tank once it has been run. This is the same kit and the same job, and you come out the far side with a CP3 instead of the pump that would have failed later anyway. If it happened today, stop — do not start the engine again — and call us.
Warning Signs
If you see any of this, stop driving it.
A CP4 that has started shedding metal will not get better with miles. Every mile after the first sign spreads debris further into the system:
- Hard starts, long cranking, or a no-start after running fine
- Rough running, stumble, or sudden loss of power under load
- Fuel pressure or rail pressure codes such as P0087
- Metallic glitter in the fuel filter at service time
- Fuel smell or visible debris when the filter housing comes apart
Catching it at the filter is the difference between a $4,700 conversion and a $12,000 system replacement.
Get It Checked
The Math
$4,700 now, or a fuel system later.
| Convert to CP3 | Keep the CP4 | |
|---|---|---|
| Failure risk | The CP4.2 is off the truck — the failure mode no longer exists | Present for as long as you own it, and it climbs with miles |
| Tuning | None required. Factory calibration stays in place | N/A |
| If it lets go | Not applicable | Pump, injectors, rails, lines, and tank all come into play |
| Cost | $4,700 installed | $12,000 installed to put it right afterward |
Also running Ford 6.7L Powerstrokes?
Ford's 6.7L uses the same family of CP4 pump and fails the same way. If your fleet mixes GM and Ford three-quarter and one-tons, we can inspect and schedule both platforms in one visit. See Powerstroke CP4 and DCR services →
Questions
About the LML CP3 conversion.
Is going from a CP4 to a CP3 a downgrade?
Only in name. The CP3 is the proven Bosch pump that GM used before the CP4.2, and it does not have the failure mode that destroys fuel systems.
You are not giving up capability — you are removing a failure point. For a truck that has to work, that is insurance, not a downgrade.
Does the conversion need tuning?
No. The Fleece Performance kit requires no tuning and no FCA regulator table changes.
It is 50-state compliant and carries CARB EO# D-834-1, so there is nothing to explain at inspection time.
What is included at $4,700?
A complete Fleece Performance kit with a new Bosch CP3, moulded feed and return hoses, high-flow fittings, and a valley feed line for later lift-pump support, installed. It fits 2011–2016 Chevy/GMC 2500HD and 3500HD 6.6L LML.
Feed pressure to the CP3 should stay in the 5–6 psi range with this kit.
Why can't you just replace the pump after a failure?
Because the debris does not stay in the pump. Metal scores injector internals so nozzles never seal correctly again, settles in the rails and washes into anything new, and cannot be flushed out of high-pressure lines at those pressures.
That is why the post-failure repair is the $12,000 contamination kit: eight injectors, both fuel rails, the pump-to-rail lines, all eight high-pressure injector lines, the crossover line, the return line assembly, and the CP3 conversion itself.
I put DEF in my diesel tank. Is that the same repair?
Yes — and stop right now. Do not restart the engine. DEF in the fuel tank and water in the fuel destroy the same components as a CP4 failure and take the same kit.
The upside is that you come out of it with a CP3 instead of the pump that would have failed later anyway.
What are the warning signs of a failing CP4.2 on an LML?
Hard starts, stumble under load, code P0087, and metallic glitter in the fuel filter at service.
Pricing assumes the failed injectors and pump return as cores; core charges are quoted in writing before anything is ordered.
Retire the CP4 before it retires the truck.
Tell us the year, mileage, and whether the truck is stock — we'll get you a firm number and a date.