Is my lift pump dying?

[JJMiller]

Today on a trip from VA Beach back to Richmond, VA, I saw my fuel pressure guage doing some funky stuff. With my foot off the pedal, it was always a rock-solid 12psi (normal idle for my rig). Before today, when I stepped on it, it would drop steadily and would bottom out around 5psi. Based on other threads, I thought I had a "healthy" lift pump.



Today, however, the needle would jump around from 2 or 3 psi up to 7 or 8, then down, then up, then back to 10-ish (normal cruising pressure for me). It would hang out there for a while, then bounce around again. At idle, it was still a rock-solid 12.



At first glance, I thought it might be an electrical problem because the guage was so erratic. I still havn't completely ruled that out. Is this type of erratic reading consistent with what anyone else has seen before lift pump failure?



SSL, thanks.



--J

P. S. What's "Post a poll?" I'll click it and see... .

 

[csutton7]

a bad electrical connection can cause that guage to go nuts--so start there first if that's not the prob--then buy a new lift pump---chris

 

[Steve St.Laurent]

I'd check your connections first, especially the ground. Run the truck and have someone sitting in it watching the gauge and wiggle things around to see if it reproduces. You say at idle it's fine, is that at idle driving down the road or at a stop? If at a stop try it driving down the road (bumpy road preferrably). If that doesn't take care of it then I'd say it's your lift pump. My current one is acting that way sometimes right now, other times it's steady down to 2-4 psi and other times it's working fine. I'll be replacing it this weekend along with adding another pump back at the tank to feed it. Also, did you hook up two senders or just one? If two, is it doing it on the second sender as well? If it is then I'd say it is the lift pump.

 

[dresslered]

Where is the sender located? Those that have mounted them on the engine (especially at the input to the injection pump without a snubber) have seemed to experience a higher rate of sending unit failures (yes, I know there are exceptions). This is often what happens just prior to the sender failing.

 

[OILBRNR]

Got my gauge installed yesterday. Everything seems OK, but I'm amazed at how the pressure drops to 2psi at WOT and higher RPMs. I think that any positive pressure is OK, but I find it hard to believe that these lift pumps couldn't keep up with that kind of demand. That VP44 can't be putting all that fuel into the engine, if it were, I'd think you could actually watch the fuel tank gauge drop!



Is it possible that at higher WOT demand, the VP44 is flowing more fuel for cooling, thus giving us these low "oh my god," no psi readings?



Otherwise:

7 psi at 65

12-14 idle

 

[Bigsaint]

John, if all leads are tight, then prepare for a replacement. Mine started doing this (the 1st Mallory) for about one week prior to meltdown. I, to, attributed the erratic readings to the electrical sender, but I was wrong and found out the hard way.



Scott W.

 

[Steve St.Laurent]

Oilbrnr, 70% of the fuel going to your VP44 is being returned to the tank for cooling and for lubrication. I can tell you that my lift pump is working variably right now, when it's working good I see a low of 8 psi at extended WOT (with my PM3 on level 9) and I hit 40 psi of boost and get lots of black smoke out the pipe. When it isn't working good (hit or miss which will happen each time you roll into the throttle) it's hitting a low of 4 psi and when that happens my boost is down to 34-36 psi and just a hint of black smoke coming out the tail pipe, also my 1/4 mile times were down by nearly a full second at Thunder in Muncie due to this lift pump problem. In my case 4 psi of fuel pressure is DEFINATELY not enough to feed the VP44. The service manual is very clear that the lift pump should have a minimum pressure of 10 psi at 100% duty cycle except when the engine is cranking, and then it should have a minimum of 7 psi with a 25 percent duty cycle with the engine cranking. I'm quite sure they wouldn't have put those specs in there unless there was a good reason, because they would be replacing more lift pumps than necessary under warranty. JMHO



-Steve

 

[DHatfield]

My guage started doing the same thing as yours this past weekend so I took it to the dealer to get it checked out. Well they replace my lift pump under warranty as it was getting a little weak.

 

[tmacc]

Steve,

Where in the manual does it state the 10psi minimum? Mine's going in tomorrow to check a few things and I want to bring this to their attention. BTW w/ EZ and BD1, it will drop to 0psi at WOT if I don't watch it.

Tom

 

[Steve St.Laurent]

In my '98 service manual it's under description and operation at the beginning of the fuel system section - page 14-5.



-Steve

 

[tmacc]

Thanks Steve,

FWIW guys it's 14-79 in the '01 manual.