Engine/Transmission (1998.5 - 2002) Is my lift pump failing?

[99slt]

I just completed installing my Isspro fuel pressure gauge today, and now I think I may have a weak lift pump.



The truck is a '99, only modifications are a Banks 4" exhaust and a S&B Filters air intake.



I installed the sensor in the port on top of the fuel filter like that paper from Geno's told me to. At idle it started at 10psi but then settled to just shy of 9psi. Driving the truck normally (I tend to baby it), it's around 6psi. Just to see what would happen, I stomped on it once and the pressure dropped down very fast to 4psi, and probably would have gotten lower but I didn't want to risk hurting anything and let off right away.



The numbers seem low, but if I drive it appropriately and don't beat it up, can I nurse this lift pump for a little longer without damaging the injection pump? I'd really like to not spend $275 for the FASS DDRP right now if I can avoid it.

 

[JLandry]

How long has it been since you've changed the fuel filter? A dirty fuel filter will result in lower fuel pressure measured post-filter.

Do you have a lift pump in the original location on the engine block or an in-tank retrofit lift pump?

In either case, those are low pressure readings. For the health of you VP44, the fuel pressure supply should stay at or above 5 psi at all times (wide open throttle under load being a worst case operating condition).

Best regards,

John L.

 

[99slt]

I just replaced the fuel filter last oil change, which was 250 miles ago. The truck only has 55k miles on it btw. I am fairly certain the port I used on top of the filter housing was pre-filter. I put it where the instriction sheet from Geno's Garage suggested.

I have not looked yet to verify, but I am assuming it's an original block mounted pump. I've only had the truck a year, and the original owner never mentioned anything about reloacating the LP.

 

[JLandry]

Yes... if the pressure readings are accurate and pre-filter, that's not good.



Assuming you do have a block-mounted lift pump, a lower-cost alternative to a FASS, etc. is to simply replace it with an Airtex gearotor type lift pump. The Airtex is a direct replacement fit to an original Carter, is more reliable, and is usually carried by most chain auto parts stores as well as RockAuto.



Good luck,



John L.

 

[99slt]

Thank you JLandry, I just ordered an Airtex pump from Rock Auto. I didn't know they made pumps that fit it the original location, other than the FASS and Raptor replacement units. I assumed all the other aftermarket suppliers switched to the updated in-tank units.

Thanks again, I hope this takes care of it.

Generally speaking, what should the pressures be around with a good pump?

 

[JLandry]

Generally speaking, what should the pressures be around with a good pump?

I'm using an Airtex lift pump. At the VP44 fuel inlet (post-filter) I'm seeing 15 to 18 psi at idle (depends on fuel temperature, which presumably effects viscosity), about 13 psi at cruise, and 8 psi under load at wide open throttle.

If after you install the new lift pump the pressures are too low, you'll have to investigate the possibility of a restricted fuel pickup screen in the tank.

Regards,

John L.