Engine/Transmission (1998.5 - 2002) Fuel pressure varies

[DAvaux]

Fuel pressure drops to 3 or 4 psi sometimes lower. Then if I shut the truck off and restart it brings it back up. It may be fine for a few mile then it drops again. Sometimes I can drive all day and it is fine. I had replaced the fuel filter and I put another fuel lift pump in. Did I get a bad lift pump or is something else wrong? The truck runs fine even with the low fuel pressure readings. I was reading these pressures with a westach guage and now I am reading the same pressures with the pressure guage in the Edge Juice Attitude.

 

[BWagnaar]

My truck did the same thing, psi dropped to 4-5 i couldn't pull over for about 5 minutes. Shut the truck off and restarted, psi went back to normal 13-14 at idle. This happened maybe 5 months ago and it only happened once.



Wish i could offer some advise. My truck has been running irracticly some times now, don't know if that has anything to do with the low psi one time.

 

[IRNGOAT]

My truck has been doing that also, sometimes if I stomp the throttle hard the guage will wag a few times and then jump back up to full press. for a while.

 

[DMannon]

Does it do this all the time or does it change with the level of fuel in the tank? Does it ever hard start? Ever have to bleed the injectors?



If fuel level affects it, you might be getting air in the lines from a dislodged, bad, or dirty fuel pickup, or the little red cap might have been left on your tank vent and you're building vacuum. Does the tank suck real hard when you go to fill up?



If it hard starts or you've had to bleed the injectors, probably air in the lines.

 

[DAvaux]

It does it at any level of fuel in the tank. It has never hard started and I have not had to bleed the injectors. When Changing the fuel filter it takes about 15 to 20 lift pump cycles (did this on the old lift pump and the new one I put in) to get it going, but then it runs fine.

When filling the tank I do not notice any problems.



Would a FASS fuel delivery system take care of this problem?? And do you leave the old lift pump in place? How dificult is the FASS to install? Does anyone have detailed instructions on the FASS installation??



Doug

 

[DAvaux]

Last night took the truck into town for dinner. I set the Juice Attitude on stock. Drove maybe 15 miles and the pressure was staying at 10 or 11 cruising speed and 13 no throttle. Then I hit a small hill and it dropped down to 4. It stayed at around 4 even idling until I shut the truck off and turned it back on. Then the press was back up again.

 

[Bob Cochran]

My truck pretty much acted just like yours and everyone thought it was the lift pump. I moved the pump back to tank on the frame rail with the Vulcan 1/2' relocation kit. It helped a lot but not completely. Replaced the lift pump with a new $70 campaign pump and it cured the problem for awhile but it is starting to do it again. I think if the pressure starts to stay low enough to worry me I will invest in a Fass, Rasp, Waldpro, to hopedully cure the problem for good. Just to let you know your not the only one for sure out there with this problem so you don't feel lonely. It is so frustrating to just want a reliable truck and something so simple as a lift pump can be causing soooooo much problem. It just does not seem right; I mean this should not be brain surgery and for sure none of this is new technology!!! Good luck and if you find some magic cure let us know.

 

[IRNGOAT]

After talking to another member (mechanic) who has had this same problem I think that I'm going to swap the overflow valve in the injector pump before I change the lift pump. I'll post results

 

[SAronson]

I've got the exact same symtoms, and I was wondering if the overflow valve was releasing too early/ erratically. Let us know ASAP if the valve was the culprit!

 

[NoSeeUm]

My first and second LP's did this exact same thing. The first one would go to zero psi at times.



Jim

 

[DAvaux]

So, did the thrid lift pump fix the problem?

 

[DAvaux]

Just went outside and cracked open the overflow valve on the vp44. Bumped the starter to bleed out the lines. Took it for a test drive and it seems to be working okay. I was getting 13 to 14 psi idle and 7 to 8 WOT. I then turned the Juice attitude up to 4 and at WOT the fuel pressure went to 3, but came back up when I lifted the throttle.

either I had air in the line or possible overflow valve was sticking, I don't know.

I am still going to put a FASS on it.



Doug

 

[NoSeeUm]

So, did the thrid lift pump fix the problem?

Yes it did. The third pump seemed rock solid. I still use it today as an installed but not used back up in my current fuel system. All I have to do is swap the wire connection and re-position a couple of valves.



In my case just like you, I got a little overfueled for the OEM fuel supply system to handle. The Carter in the stock configuration supplied 14 psi at idle and 3 psi at WOT. The Carter in the relocated configuration supplies 14 psi at idle and 11 psi at WOT.



I now use a Mallory regulator with a Walbro 391 for my fuel supply. The Walbro set up seems rock solid with anything I throw at it. It supplies 16 psi at idle 14 psi at WOT.



Jim

 

[DAvaux]

Spoke to soon. The pressure is still not good. It is now going down to about 7psi idle. Then again after cycling the engine it goes back to 13psi. IRNGOAT was going to replace his overflow valve and let me know if it fixed his problem.

 

[Bob Cochran]

Forgot to say in my earlier post that I did change the overflow valve and it made no difference for me. Though for some it did help. Sure is one of the cheaper things to try however.

 

[DAvaux]

Stopped by Cummins today and picked up a overflow valve. They called it a check valve. Installed it and it did not fix the issue.

 

[DMannon]

Disconnect your fuel line at the VP and let it flow in a bucket. Bump the starter and watch fuel flow. It should flow clean and clear, no bubbles or foam. You should get about 1/2 gallon in about 20 seconds.



If it's foamy or has bubbles, you're getting air in the lines. If you don't get 1/2 gallon, your pump is not pumping enough (either a bad pump or plugged fuel pickup or?).



Look at the whole system from the tank to the VP... lots of places to suck air or plug the system causing the LP to cavitate.



Do you have a big line kit on it? Try disconnecting in front of the tank and blowing a little LOW pressure air back into the tank. If it runs well after that (don't forget to bleed the system), you might have a crudded up fuel pickup.

 

[DAvaux]

A FASS Fuel Delivery system (FASS 150/95-1008) should be here on Friday. I will run these checks at that time so I know what was causing the problem.

 

[RustyJC]

What fuel pressure gauge are you using? If it's electric, verify your readings with a mechanical gauge before throwing too many parts at the truck. I've had Westach fuel sending units give this intermittent behavior as well - replacing the sending unit took care of the problem. In my case, it's easy to spot because I have a Westach dual combo fuel pressure gauge that's reading pre-filter and post-filter fuel pressure, so if only one gauge acts up... .



Rusty

 

[Holysmokes]

What fuel pressure gauge are you using? If it's electric, verify your readings with a mechanical gauge before throwing too many parts at the truck. I've had Westach fuel sending units give this intermittent behavior as well - replacing the sending unit took care of the problem. In my case, it's easy to spot because I have a Westach dual combo fuel pressure gauge that's reading pre-filter and post-filter fuel pressure, so if only one gauge acts up... .

Good call I was going to ask same question. I had the same issue and come to find out the "bellow" in my cylinder style fuel isolator was shot (after 3 months) went to pancake style MUCH BETTER!