Lift pump blues

[DFleming]

I have a 91. 5 that the lift pump went out, so I went down to the local part



store and got a airtex pump, put it on blead the system and she ran rough at



first then idle out fine. Shut in down to put the tool away and went to start



it again and didn't get jack it just crank and crank so I blead the system



again and it ran fine. So far I have let to figure out what it is, I have tried



clear line to see if I am sucking air and it showed that I was so I replace the



hard line with a soild rubber line from the tank forward and still the same



problem. O bye the way it can run all day after I bleed it at idle but you drive



it down the road and it will dye like it ran out of fuel. So I thought



maybe the pump wasn't strong enough for the engine so I bought a cummins



lift pump and still the same thing. I am looking for help with this



or I am going to put a 30. 06 AP round through the block. #@$%!

 

[JLEONARD]

If it were only ONE pump I would say the pump was no good, but since you have the same symptoms with 2 pumps I would suspect you are getting air in the fuel lines some place.

What I do to troubleshoot is pressurize the ststem somehow to find the leak.

I have used an air gun (wrapped with a rag) into the fuel fill... that will give you a couple of psi which is enough to find a leak.

I have also used an outboard engine squeezball rig to pressurize.

Both work.



When my lift pump went is had some of your symptoms. I cut the pump apart and found that one of the rubber "check valves" inside the pump failed. I really was glad to find the root cause.



Hopefully this helps. Save the AP round for something else.

 

[DFleming]

Thank for the help I am going to try that this weekend and if that doesn't solve it I shall return.

 

[DFleming]

Well I tryed the rag trick with no luck so if someone else has any other tricks



to try let me know#@$%!, it's about 10 mintes and the truck just barely



wants to start because to whole system bleeds off. On a different note does



the brake booster have anything



to do with the fuel system because the damn thing is leaking and I just put a



new one in and its leaking air and it bleads on off like you open a air valve



and blead off in a rush and it is over.

 

[ChrisWilliams]

Since you replaced the line from the tank to the lift pump and you pressurized the system and did not find any leaks. I suspect your problem is inside the tank. There is a small hard rubber or plastic line that hooks on the elbow in the tank and runs to the bottom of the sump. Either this line or the plastic elbow has a split in it, causing the system to get air. The tank pressure test will not show this problem. Before you do anything else, triple check the fuel line from the filter back to the tank to make sure you haven't missed anything. If all is well, either pull the bed or drop the tank and check the sump. I pulled the bed because I had a full tank of fuel, and put in a vulcan draw straw that works well. You could use the clear line again to make sure you are still getting air. How much fuel is in the tank? If you cover the hole with fuel by filling the tank, no more air. If the hole is at the very top of the tank, this won't work. The best way to fix your problem given what you have already done, is to finish replacing the fuel system from the lift pump through the tank. Good luck and let us know how it goes!

 

[DFleming]

I dont think that it is the draw straw because I have drawn the tank down



this far before with no problem. Is there a check valve in the injection pump



or is it in the lift pump. #@$%! So anyone that can help me with this bull****



would be very help full thanks again with all the help. :{

 

[JLEONARD]

this far before with no problem

The draw tube can break/fracture at any time. Just because you could draw that deep last time doesn't mean you can now.



So here's another one that just came to mind... this happened to me last fall... . I started to have truoble starting... lots of cranking. What happened was the fuel line comming out of the tank had corroded thru. The starting got harder as a week progressed... then finally I saw a wet fuel spot under the tank and knew I had a leakng line.

But it was sucking air for a while before the leak became obvious.

I think you would have found that with the air gun and rag procedure though.



You could blow air back into the tank from the fuel pump inlet... . that might tell you that the draw tube is good or bad. Just a thought.