# Lift pump



## Blasirl (Mar 31, 2015)

Way above my pay grade!


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## Ma v e n (Oct 8, 2018)

The 6.6L Duramax produced from 2001-2016(LB7,LLY,LBZ,LMM,LML) and used in the fuel sized pickups don't have a lift pump. The Bosch high pressure injection pump sucks fuel from the tank and creates the high pressure. All in one unit.

With the amount of power these things can make they benefit from a lift pump assembly (which is almost always equipped with a small micron fuel filter, water separator, and an air/vapor separator as a complete unit)

Additionally the 2011-2016 6.6L uses a Bosch CP4 twin piston pump, which is very sensitive to water, air/vapor, and the low lubricity of ULSD fuel.(ultra low sulphur) These trucks are prone to catastrophic failure of the pump and then an ensuing complete contamination of the fuel system with metallic debris from the rollers and eccentric inside the pump. Outside warranty this is an $8000 minimum repair bill for a proper complete repair.

Only religious filter changes, high quality clean and dry fuel, and lubricity additives (or luck) are the sure fire way to avoid the issue on a stock fuel system truck.

Lift pump/filter assembly unit on these "CP4” trucks take away some of the risk of premature failure on these engines.

Both the 2.0 LUZ and 1.6 LH7 Cruze engines come with a lift pump. Using a nice fuel lubricity additive like OptiLube XPD, FPPF Lubricity+, AR6200 and others would aid in avoiding any excessive premature fuel system wear due to scarring from ULSD.

This week's LML fuel system replacement....


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## TDCruze (Sep 26, 2014)

^^^ Very interesting. 

I have not heard of any fuel system failures in the diesel Cruze's, but sounds like a lubricating additive might not be a bad idea.


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## Ma v e n (Oct 8, 2018)

I'll post some more pictures or maybe a separate thread with some CP4 Carnage later.


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## MRO1791 (Sep 2, 2016)

The CP4 pump is a cam roller piston design and it's a horrible design. The trucks, GM and Ford use them, and VW used a 1 piston version. All of them have seen these catastrophic failures. The Cummins Ram/Dodge stayed with the better more expensive CP3, which is a crank shaft 3 piston pump. The Cruze uses a similar design as well. It's the big factor in my ditching the VW for the Cruze. Having VW tell me metallic particles in my fuel filter was "normal" and charging me to tell me that crap was the final straw.. this within days of the new breaking over the emissions cheat. The cheat saved $300/car.. the crappy CP4 saved $600 per car. 

Sent from my Moto G (5) Plus using Tapatalk


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## Ma v e n (Oct 8, 2018)

Both the CP3 and CP4 variants used by Duramax(and Cummins and PSD) are radial arrangement, multi-cylinder, polygonal ring/bucket actuated plunger style pumps. 

That is a bucket rides on a polygonal ring(just like a valve lifter riding on a camshaft lobe) a spring is in the bucket and holds it's against the ring/camshaft. The bucket actuates a plunger shaft(much like a pushrod in an OHV engine valvetrain) which moves the high pressure valve(piston) in the pumps cylinder to compress the fuel and send it out the fuel rail.

The largest fundamental difference between a CP4 and a CP3 is that the CP4 has a roller bucket, and the CP3 has a flat bucket. The CP3 is a 3 cylinder, the CP4 is a V-twin.

One major problem is that without a positive pressure fuel supply( external lift pump) it's somewhere between possible and garaunteed that the pump will experience cavitation(destructive air pockets induced inside the pump).
Water is also destructive to the pump internals as well, offering even less lubricity and promoting corrosion(I've seen pumps corroded from water in contaminated fuel)
Additionally the CP4 used on these engine is designed to used fuel that has a lubricity rating that limits scarring to 460 microns,However US #2 diesel fuel only has a 520 micron scar lubricity specification. Bosch has stated (in documents I can't find anymore...) that a 500 micron score could result in a 1000hr lifespan. (Less than 40,000 miles for most people)


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