Cummins Diesel Forum banner

Lift pump test question

7K views 33 replies 7 participants last post by  D-Rex 
#1 ·
yesterday for second time in the last month driving along fine--- suddenly just not running stalled out without much drama.

First time it happened, put new filter on, primed, got running again. Put a new OFV on cuz it's easy. Fuel pressure gauge in driveway/ underhood seemed good within spec w/ Tork Tec 20ish idle 30ish @ 2500rpms

At that time I wondered if the stall out was contaminated fuel/ iffy tank module


Has run fine untill yesterday---same thing running fine and suddenly stalled out without any drama/ no coughs bucks etc. just huh? wha? coasting to side of road.

This time I can not get any fuel primed/ pulled thru. At first I thought maybe I had the 1/2 tank syndrome where something is frigged up with pick up straws in tank module so they aren't sticking into fuel anymore. I put another 10 gallons into tank to see if I could get any fuel primed thru---- no joy---and I have pumped the heck out of the primer/ have the bleed screw loosened etc.

so--- next I wondered about lift pump---so I did a test but I'm not sure if my interpretation is correct. I have rubber trident lines/ w hose clamps at the tank----was very simple to undo the supply line and stick it down into a fuel can of diesel---pumped the heck out of the primer........still no fuel pushing thru

does this probably mean the lift pump is shot?

I have not done my fuel heater--- would it be sucking air so bad that I wouldn't be able to even manually prime it?
 
See less See more
#2 ·
Sounds like a bad one to me. I think the Tork Tek should be running at a preset psi of 30, so that would point to a weak lift pump. I'm having a similar issue where my pressure only runs at about 20 psi and if I'm at WOT it'll drop down below 10 and I have a Tork Tek Adjustable OFV, so I just pulled the starter to replace the lift pump today. Have you tried installing a cheap electric fuel pump to see if it'll get the truck running?
 
#3 ·
does this probably mean the lift pump is shot?

I have not done my fuel heater--- would it be sucking air so bad that I wouldn't be able to even manually prime it?
No, the primer button is independent of the pump that is actuated by the cam.

Yes, it could.

However, neither explains a sudden shutdown. Air in the lines is constantly suggested by inexperienced members for a variety of things that are not even related. My first thought is the FSS is losing power and the arm is falling.
 
#5 ·
FSS Fuel Shutoff Solenoid? Yes it may very well be---I did also discover my positive clamp on the driver side battery was loose both breakdowns. First time I tightened it up and looked fine, not corroded-- 2nd time yesterday the lead on the clamp had cracked so it was staying on but not snug

or the solenoid itself---I haven't done any thing to it (yet)

the lift pump I assume is original--if it is it's got 280,000 on it.

I can't get it to prime/ get any fuel thru to bleed. Cranking it cranks but doesn't get any fuel----- the first break down I did have to pump the heck out of it to get fuel flowing---and I did make sure the FSS was in run position before cranking----- I'll do that agian just in case.....but at this point I may have got all kinds of air in the the lines and what not frigging around

any other trick to get the fuel moving since my primer is giving me no joy ( I have pumped a million times, and then a million more to be sure)
 
#4 ·
I haven't done anything yet

Thoroughbred diesel seemed to have a good price on lift pump few weeks ago compared to others when I priced them couple weeks ago (but then it was running fine so thought I was all set ;(----- where'd you get yours?

I can't remember now--I didn't write down my pressures and don't recall exact off top of my head BUT the info sheet w/ the Tork Tec says it idles around 22ish and it is set for 30 @2500rpm---- I don't have the stuff in front of me but I do recall it says it idles around 22 w/ Tork Tec

I've never messed with lift pump--- how are you finding it to replace? Looked like it was not especially "hard" per se but more PITA to access
 
#7 ·
If the primer isn't working I would replace the pump. I don't think that is your problem. You can push 10 to 15 psi of regulated air into the fuel filler pipe to prime the system using a nozzle wrapped in a rag.
 
#8 ·
yes OK-- I went out and made sure the FSS was in the run position--- and it did sound like it had a whisper of fuel trying to start......but then the baterry crank rapidly sank too low.

This is essentially a wash rinse repeat of the last episode---I got distracted by the not being able to prime it via button ---did not check the FSS position when I tried to restart

Have it hooked to a charger--- if it is like last time, full charge, couple cranks and stalls and then it ran....but yes I did get out every time and make sure the FSS was in run before cranking it over that day. Hope I didn't get a whole bunch of air in the line fiddly farting around chasing the fuel side. My neighbor has an aircompressor I think.

I've changed the connector on the battery positive terminal Driver side that has everything hooked to it---it wasn't corroded at all but everything was pretty loose and the clamp around the post had cracked. I had that one put on at a garage last year some time.

will get on the FSS deal and Lift pump
 
#9 ·
When my lift pump took a crap I had no fuel pressure
 
#10 ·
I will mention that yes the primer is a independent pump, but it still uses the same check valves.

I was trouble shooting zero fuel pressure and almost no fuel flow, and tried priming it and the primer was very hard to push. Sure enough the output check valve wasn't opening all the way, replaced it and it's good as new.

A few years back I had a problem with the truck in my sig dieing on the highway, the quick connect at the tank wasn't making a seal and was letting air in, no amount of priming was ever going to get fuel to flow.
 
#12 ·
#15 ·
BTW--- I've read the stuff about the injection pump being able to draw the fuel thru without the lift pump---but I also saw some mention this could be quite bad for the injection pump---but is that just for the 24v VP44, or does this apply to us with a 12V as well?

I plan to fix it, just wondering if I get fuel to engine again with air pressure from tank---at least get it running if it's Ok to drive around town till the parts get here or better to just not run it at all

as Games said earlier--- not really clear what caused the sudden stall out lost prime. May be more than one thing---iffy lift pump, loose battery connections effecting FSS causing arm to fall while driving (or just plain iffy FSS).... and potentially cruddy stuff in tank

regarding the FSS arm dropping while driving---would that cause lost fuel prime that required bleeding?
 
#25 · (Edited)
Doesn't make much sence that the fuel pressure is going down when you do the pinch test... Are you sure you are pinching the return and not the input?

With 22psi @ idle, it sounds like your lift pump could very possibly be in good shape, like others said, check it @ 2500 and that should tell you a lot.

EDIT;
Coachjvinson, I got some pics of the output check valve, just need to upload them later on tonight.
 
  • Like
Reactions: coachjvinson
#26 ·
I will recheck everything tomorrow-- but unless my eyesight went hay wire I had the return line

the fuel pressure had come down to 15-17 when I restarted it after getting it finally started and then turning it off for 30 min-----it has been running right around 22 with the tork tec untill this afternoon

but I need to recheck all the hose clamps and things I had loosened fiddly farting around today to be sure they are all tight
 
#29 ·
boy if it weren't for these forums and youtube with info and demonstrations I would be so SOL on this stuff because I am no auto mechanic I just have learned how to deal with things on the old 12 valve along the way (often because some garage has charged me a bunch for a fix that wasn't "fixed' ;( !!!) And forget it now, age of vehicle they don't even care or want to deal with any of it----just get a new one attitude...but I like the old truck and it's taught me anything I know about tinkering....I'm not ready to "graduate" to something with $40k-50K price tag and all sorts of "improvements" .....
 
#31 ·
Normally if you pinch the line and the pressure doesn't spike the lift pump is worn out. Since you have pressure it won't hurt to drive it, but I wouldn't go far from home until the new pump is installed.
 
#32 ·
OK-- do you have a recommendation for a replacement pump source to buy from? --I'd don't want to buy some cheap crap that is f'd up again next yer---don't know what to look for to make sure I am getting good quality

The FSS is starting up and turning off normally in driveway---- I would not be suprised if the loose battery clamp and FSS had something do with both stall outs beside the road-----that then a not super healthy lift pump complicated matters.

Battery clamp is all fixed---I have not messed with FSS

I've got a neighbors truck to drive.... he's been driving around with the drivers door handle busted off (very poor design 01 chevy)----I just replaced it for him $30 bucks for the handle easy peasy.....so I think I'm in good to keep driving his truck for a few days :party018:
 
#33 ·
Genos has them for a hundred or so that come with studs (which makes install a lot easier) and two gaskets. Someone posted recently a place that has them for about $85, but I didn't bookmark it. IDR if it came with even the gaskets.
 
#34 ·
TB Diesel has them for $85 no extra shipping. Made by "Alliant Power" says it comes with 2 gaskets Fuel Transfer Pump Alliant Power Stock Replacement Dodge Cummins 1994-1998 5.9L

Genos is $120 and specifically says it comes with everything gaskets and the studs.

From what I am hearing the studs are worth the extra $35 ! I also looked it up ---if get the TB diesel and then buy the stud things seperately....only save like $6 after shipping yadyada
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top