Engine/Transmission (1998.5 - 2002) Fixed my lift pump !

[JerryHammock]

I have been chasing a problem with my lift pump now for about 6 months. Driving down the hiway, cruise set at 60 - 65, and the fuel pressure gauge is all over the place between 12 and 0 psi [mostly 0 psi].



I have worn out the bolts changing lift pumps, installed the Vulcan relocate kit [a very nice product, thanks Eric], called about every vendor in the TDR, nobody knew how to fix the problem.



Yesterday I bought a Superchips programmer, and installed the perf tow option, and the fuel pressure is rock steady at 12 psi. I noticed that when I turn the key on, the lift pump only cycles for about a second now, where it used to run for several seconds before the upgrade. Also, during the upgrade, the lift pump cycled a time or two, so I have to think that the lift pump function is part of the upgrade.



I have not driven enough yet to see if I got any performance from this upgrade, but if it only fixed my lift pump pain in the *****, then it was worth the $$$$ that I spent on it. Maybe saved me a VP-44 and some real BIG $$$ down the road.



Hope this helps someone else with the same issue... . Happy motoring!

 

[Gary - K7GLD]

Seems that later trucks only cycle the LP for about a half second at key-on to prime the system for starting - then, once the engine starts, the LP begins normal pumping operation. Your mod apparently also adds that LP function.



I suspect the earlier, longer LP operation during engine starts allowed fuel pressure to rise above cavitation pressure inside the LP because there's no actual fuel flow thru the LP to speak of until the engine starts, and it never recovered normal pumping flow/PSI after that. The lower time LP initial operation with your mod likely avoids allowing cavitation to begin, and once the engine starts and normal fuel flow is begun, the tendency to cavitation is gone or greatly reduced.



I've personally witnessed that tendency of the LP to cavitate at the upper limit of it's PSI range when I had one on the bench doing some flow testing - and once cavitation was started, the only way I could stop it and restore normal flow, was to shut the pump completely off, and restart it - it's seemed to get into a vapor lock condition that it simply would not recover from while power was applied.



My setup will do the same thing if I add too much oil (either 2-stroke oil for lubricity, or used motor oil) to my fuel. That apparently alters the viscosity of the fuel, or increases it's tendency to foam - once normal fuel percentage is resumed, the cavitation goes away.



Meanwhile, all that saves my fuel pressure is my lower PSI Carter pusher pump, which seems to be unaffected by changing fuel characteristics, and actually FORCES fuel flow thru the LP - helping it recover from cavitation it would not do otherwise.

 

[JerryHammock]

Mine is a Carter L/P also.