Engine/Transmission (1998.5 - 2002) Fuel Pressure Fluctuation

[Motorhead]

Put guages in my brothers '01. 5 HO yesterday. We started it up and all was well. As we drove it, it all of the sudden we had the fuel pressure drop from 12psi to 6psi. It idled at 14 then 6psi. We shut it off and re-started it and the pressure went up to normal for awhile then suddenly dropped to 6 running and 2 at WOT.



I checked it at pre-filter with a test guage and it confirmed what we were seeing on the elect (Westach) guage. This AM, I took out the pressure relief valve on the inj. pump and blew it out and checked it to see if it was hanging up in any way. We put it back in and the pressure was good. My brother then took off to go home (225 miles away) and he called me and said all was well. He stopped to eat and when he re-started it, it was low again. He found that he could drive over bumps and the pressure would shoot back up to normal.

Has anybody had problems with the ck valves on the VP 44 or do you think that it is something else. Chris

 

[Shooter]

Someone needs to play a funeral dirge for the lift pump.

Isn't that why you are monitoring the fuel pressure: to keep tabs on the lift pump

 

[Steve Campbell]

I agree with Shooter...

The "spill back valve" spring, in the lift pump, is giving up on you.

 

[Big White Beast]

Intermitent.........

Checked a friends once and it was at 0 PSI. We hooked the mechanical gauge under the wiper and went for a drive. Once we got some speed up it jumped up to 13 PSI. Come to a stop and it dropped to 0 PSI again. Funny but when the VP helped it out it seemed normal.



Dealer replaced his under warranty. It isn't worth taking the chance even if you have to pony up the $150 for it.



Garrett

 

[wyosteve]

Did you mount the sending unit someplace other than on the engine and did you use a snubber? When the bozos at the garage mounted my sending unit on the valve cover, despite my directions not to, my pressures were all over too. I moved it away from the engine and all was well. But having said that, it probably is a dying lift pump.

 

[willyslover]

at the very least. . get him a spare in his truck box. . so when it does give up he has a ready to go unit. . IMHO change it out now

 

[tgbol]

It is time for a new pump. That is exactly the way mine died.

 

[Motorhead]

So there is a ck valve in the lift pump that can cause this? One minute it is normal then it drops suddenly. That is why I checked the return ck valve on the inj pump.



We mounted the fuel sender away from the engine.

Chris

 

[andrewkoperdak]

I get the same thing every once in awhile. Seems my Xfer pump cavitates a bit and puts airbubbles in my gauge line. Once the air is there it bounces as you have described. I simply unbolt my gauge line and hang it as low as possible for about 30 min. Bolt it up and she is good for another 3k or so.