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

[Irontrader]

I installed the latest greatest version of the stock lift pump earlier this year. Everything has been great with 14-15 lbs of pressure at idle and around 12 lbs driving down the highway.



This morning on my way into work, I noticed my guage had dropped to 6 lbs!!! Plus it seemed to be dropping slightly the further I drove. Since my fuel light had come on the day before, I thought that maybe my fuel guage was stuck and the pump was sucking air and I was really lower on fuel than I thought. So I stop and refill the fuel tank (took 28 gal).



When I restarted after filling, the pressure was back to 14-15 at idle and everything seemed okay.



A couple blocks later while I was watching the guage, it suddenly dropped from 14 lbs to 6 lbs! Just like someone had flipped a switch or something. I continued on to work with the pressure returning to about 6 lbs at idle and running around 4 lbs.



A few blocks from work I pulled over and shut the engine off for a couple seconds. When I restarted the pressure was back to normal. I was only a half mile or so from work and the pressure stayed normal until I got to the parking lot at which time it again dropped to 6 lbs!



Fuel filter was changed about 10k miles ago.

I don't think the lift pump has more than 10k miles on it. I don't remember now exactly when it was I changed the lift pump.



The auto meter electronic fuel guage has been in place for over a year with no problems.



To make matters worse, I need to pull a trailer 600 miles each way this weekend, so need to figure out my problem in the next 24 hours.



So... ... has anyone else seen this behaviour and was it a failing lift pump? Or could it be the guage or fuel filter causing this?

 

[THerman]

I would say it would either be the guage sender or the pump.



I have seen this with both. The first time it was the pump... .



The second time it was the sender... and more specifically it was at the terminal (turning in the unit).



The only way to know for sure it to verify the guage reading with another sensing method. ie:mechanical pressure guage.



hope this helps.

 

[Irontrader]

I'm hoping that maybe it is just the sending unit for the pressure guage failing. I've got it screwed directly into the top of the fuel filter so I'm sure that the engine vibrations aren't good for it, but it has lasted for over a year.



I would think if the pump was failing that you'd see more of a gradual decrease in the fuel pressure rather than the sudden changes in fuel pressure readings I've seen today.

 

[rotohead]

Exactly the way my last two lift pumps went bad on me. I have two fuel pressure sending units so it's easy for me to verify pump or sending unit/gauge. 4psi was the lowest I got out of those bad pumps before I changed them out.

Chuck

 

[15w40]

Irontrader, Before you blame the lift pump for the lower pressure, try a new filter. My fuel pressure alarm just went off this week (set at 4 psi). I thought that my lift pump was beginning to get weak but a new filter brought the pressure back. The filter in my truck had about 15K miles on it, but all it takes is one or two tanks of dirty fuel to plug the filter.



After many years of driving this truck I know that if the engine is cold (cold fuel), the filter is getting plugged, and a WOT start, the pressure falls off.

 

[CrewCabDiesel]

Well Guys I might be in the same boat, Just installed my new westech fuel pressure guage and I have 8 to 9psi at an idle, WOT it drops down to 3psi. The sender is runing through the banjo bolt at the fuel filter. So am I to assume at 89,000 miles the lift pump is shot ? Do I need to stop at Cummins for a new lift pump?

Also this weekend I am adding a set of stage 2 injectors and a edge comp box.

any suggestions would be great

Kyle



ps, fuel filter has 3k miles on it.

 

[Diesel Freak]

Before you condemn the fuel pump, make sure all the air is out of the filter housing. I have noticed that after a fuel filter change my fuel pressure can be erratic (1-2 psi swings while idling). Even after a few hundred mikes, fuel pressure can get increasingly erratic.



What I have found is over time disolved air in the fuel builds up in the filter housing and I have to open the drain valve while the truck is running to vent it off. Once this is done fuel pressure is rock steady at 14. 5 psi at idle.



Also make sure all the air is out of the line going to the pressure sending unit.

 

[Evan A. Beck]

I just replaced my Carter 4601HP pump on Thursday. It lasted about 60,000 miles, so I am happy with that! Pressure dropped about 2 psi below normal, so I figured I'd take care of it befor eit got bad. But here's the interesting part... Before I swapped in the new pump, my peak boost was 39 psi. After the new pump was installed, I peak out at 43 psi. Power is a little stronger at the top en, too. Gotta love it! Next step is to get this puny HX35 offa here and put my '40 on!

 

[Evan A. Beck]

I almost forgot... Cliff, have you seen the new Holset turbos? HE series? I think you'll like them... Way cool stuff.

 

[Diesel Freak]

Originally posted by Evan A. Beck

I almost forgot... Cliff, have you seen the new Holset turbos? HE series? I think you'll like them... Way cool stuff.

nope, cant find it on their site either

 

[Irontrader]

Last night I put a mechanical pressure gauge on the inlet side of the fuel filter. It would register around 15 lbs of pressure, then drop to around 6 lbs. I did this test while the pickup was parked and it would start with good pressure then drop to 6 lbs after about 5 to 10 seconds. I did this several times and it gave me enough time to go look at the mechanical gauge and watch it when the drop in pressure occured. So I'm assuming that the lift pump is the problem or I've got a problem in the fuel pickup. I'm leaning towards the pump going bad even though it is only 4 months old.



The strange thing is that I can shut off the engine and the pressure returns to normal for a period of time. (anywhere from a few seconds to several minutes). Driving last night I even had the pressure drop and then return to normal a couple times without shutting off the engine.



What sort of behaviour have other people seen when their pump was going bad? I could understand it just suddenly dieing and having no pressure, or even a gradual decline in pressure as it wore out, but this normal pressure then low pressure isn't what I would expect.



I don't think it is a wiring problem as it happens when I'm driving or parked, and smooth pavement or wash boarded gravel roads doesn't make any difference.

 

[Steve St.Laurent]

I've had a lift pump go in the manner that yours is. Also read of many here on the board doing the same. I bought my truck with 28,000 miles on it and between 28,000 and 65,000 miles I went through 4 lift pumps - that's less than 10,000 miles each. I then got sick of replacing them and decided to do something about it, I added a pusher pump along with the last replacement and now at 110,000 miles I haven't replaced another one.

 

[Irontrader]

Steve,



This last lift pump only has been on the truck 4 months



Cummins NW has one in stock, so this afternoon I'll put another pump on and hopefully the fluxuating fuel pressure problem will be resolved.



If it does cure the problem, I'm thinking of relocating the lift pump back by the fuel tank so it will hopefully last longer.



I bought the current lift pump exactly 6 month ago. Cummins says there is a 6 month warranty on the lift pump, but it will have to be sent into Cummins for testing to determine whether it is covered or not.

 

[Irontrader]

Yahoo!! It is fixed!!



Went to Cummins NW at noon and got a new lift pump, went home and installed it. After a long test drive I'm sure that the old pump was the problem.



The newest pump actually has a bit more pressure than the prior one did when new. Also I notice that the needle on the pressure gauge is more steady than it was on the old pump. With the old pump when the engine was idling there would be a half pound fluxuation in the pressure, while this new pump is rock solid.



Maybe a twitchy pressure gauge is an indication that your pump may not be one that is going to last.

 

[Diesel Freak]

Originally posted by Irontrader

[BMaybe a twitchy pressure gauge is an indication that your pump may not be one that is going to last. [/B]

very possible!



If you want to take a look at how I relocated my lift pump, I can stop by.