Engine/Transmission (1998.5 - 2002) FP getting low?

[JohnMcCarthy]

I have been watching my gauges and the FP is usually about 6lbs when cruising and 10lbs at idle. It will drop to 0 when under full boost. The truck is stock with a 4" exhaust and BHAF. I have not noticed any change in the FP since I installed the gauges about 4 months ago, but I don't have any thing to compare to. What do you think? Thanks.

 

[keimmmo]

Sure sounds low to me. Have you changed the fuel filter lately?



Steve

 

[Jefff929]

:--)

Stock FP was 9-10 at speed, 6 WOT. less than that I suspect your LP. replace it or plan on VP44 and LP.

 

[DieselRam30]

That fuel pressure is way too low. The absolute minimum fuel pressure that you should be running is around 8 psi. My first thought though would be a dying lift pump. I would also see if the the truck is pulling any codes. If it's still running fine at these pressures, double check the gauge install too. Sorry for the bad news.

 

[TinyInOhio]

I would be either adding a pusher pump or replacing the lift pump. Otherwise you will be installing a new injection pump before long.

 

[DJW]

I was told at a Boch (spelling?) VP rebuilder, 8 lbs. minimum to preserve VP pump. Rebuild (yours) 3 days $1430. Also cautioned on position of key Scrum Down

 

[keimmmo]

Hey guys, I was the first one to answer and my first question was about the fuel filter. While it is likely the lift pump, you guys are blaming it without knowing the condition of the filter! You ALWAYS verify the cheap, easy, and normal maintanence stuff BEFORE you start changing expensive parts!!! Since I run a guage, I use the guage to know when I need to replace my filter. A partly plugged filter ALSO shows low pressure... just like John discribed.



Here is how to tell if it is a filter or the pump. Without starting the motor, bump the starter as lightly as you can and leave the ignition in the run position. That will let the lift pump run for several seconds. If the pressure with the pump running and the motor off comes up to 14-16 psi, the pump is good and it is just the filter. If you still get only 10 psi, the pump is going bad. This is how I determine which to change when the pressure starts to drop. I am on only my second lift pump with 120,000 miles on the truck. I have changed MANY filters!!!



Steve

 

[darkhorse]

My fuel pressures were running about 9 at cruise & dropping way low at WOT. Down near 1 psi. I changed the fuel lines & fittings from the LP to the IP with 8 AN. That alone kept WOT pressure from falling below 8 psi from a idle/cruise pressure of 11 psi.

 

[Jefff929]

Hey guys, I was the first one to answer and my first question was about the fuel filter. While it is likely the lift pump, you guys are blaming it without knowing the condition of the filter!

Steve,



You are right. I can tell when the filter gets stuff in it. By a change in FP, This sounds as if the FP is consistantly lower over time. That is why I didn't go there.



IMO FF is changed every other oil change on a stock system. I figgure that is just me being a fuss bucket forgetin that not everyone is that way

 

[keimmmo]

I have relocated the stock lift pump back just in front of the fuel tank. I run a 2qt spin-on pre-filter just after it. I have eliminated the banjo fittings from there to the stock filter and have drilled out the stock banjos on the outlet side of the filter and the inlet into the VP. With my combination, I COMMONLY go 25k between filter changes. Besides, up to the point that it becomes a restriction, the more plugged(dirty) a filter is, the smaller the particles it will filter out and therefore the better for the motor.



I agree that John probably needs a lift pump. But, you always check the cheap and easy stuff first!



Steve

 

[JeffWhite]

Well, obviusly D/C knows more about the required fuel pressure than

the rebuilders, see my post on my new in-tank pump

I think I'm gonna run it and see just how long the new VP last like this,

then go with a Fed-Ex pump and a RASP or FASS - or just unload the

damned thing and either get a 04-05 with a NV5600, or swap brands.

Yeah, I know, good luck there. Come on Nissan, make a real truck (DRW)!

By the way, from working on gassers, I KNOW there are lots, if not MOST

in-tank pumps capable of doing more volume (and pressure) than this,

WHY did they do this, unless they do know something? Is it true that

some European applications in box-trucks don't even use a LP? I seem to

have heard this somewhere, if it is true, how do they hold up?