Lift Pump Check Valve

[britannic]

Well the colder weather has revealed that my lift pump is in need of R&R. I opened my IP pump today to turn the fuel up and found the pump was completely drained apart from a 1/4" in the bottom. It had all siphoned back into the tank due to the fuel cooling down and my housing return hose having a tiny airleak.

I would appreciate it if someone would confirm that the GM lift pump part # 25116503 has a check valve - my old part # is obselete and that definitely doesn't have one :D .

[FredM]

thats the correct part # as per chapter 2 on hard sterting, i need one too. can a vacuum pump be used to draw fuel from the tank through the new pump, have it hold prime and then connect the pressure side?

[britannic]

Thanks Fred! The new pump shouldn't need any more than a good couple or three 15-30 second cranks, 4 minutes rest in between each, with the air bleed open on the fuel filter and the pink lead on the IP disconnected to stop it sucking air. The lift pump is mounted lower than the fuel tank and it'll start a siphon when the engine cranks.

Your idea with the vacuum pump will work though; I actually started a siphon using my lungs to prime the lift pump (don't do this at home folks, definitely not safe if you swallow diesel, fumes can suffocate you as they come up from the gut and down the windpipe) after installing the Banks turbo.

[gmctd]

The mechanical lift pump has two check valves - inlet is one-way in, outlet is one-way out.
Pumping function would be physically impossible without both valves, right?
Same for the electric lift pump, which is an impulse type.

The rotary in-tank types have only outlet check valve, requiring submersion to function.

jd

[britannic]

Originally posted by gmctd:
The mechanical lift pump has two check valves - inlet is one-way in, outlet is one-way out.
Pumping function would be physically impossible without both valves, right?
Same for the electric lift pump, which is an impulse type.

The rotary in-tank types have only outlet check valve, requiring submersion to function.

jd Thanks gmctd, I should have clarified that I meant the pump with the "ventless" check valve (excerpt from the "Troubleshooting Guide" in the Ref. section):

Since 1991, GM recommends using their new 6.2L fuel lift pump (P/N 25116503) which uses a "ventless" check valve to prevent fuel drain back. Any aftermarket brand should be of similar construction.

[gmctd]

Believe me, I was really puzzled why you would ask such a question.
I have that Guide, but I use it to mark my findings and referenced data in. That info is Emissions related - glad I posted.
Now to find my pen.

tnx
jd

[mhagie]

Funny I had never given a thought as to whether the mechanical pump on mine had a check valve, but I know the aux pump mounted back at the tank does so it matters a little less whether the mech one functions perfectly or not.
Thanks to articles here at TDP, Dr. Lee/s aux fuel filter and lift pump, sure makes things easy.
When I converted my truck to a 6.5TD from a 383 gasser using the DR. Lee method I was able to prime everything with a flip of a switch, hit the ol starter a couple of revolutions and bang I'm making smoke,it don't get any better than this except if it would have had a D/Max under the hood. :D God I wish I would have had the guts to try it..............Merle

[FredM]

this is like going to night school, but i'm not complaining. only the whole engine compartment is coated in a nice patina of black engine oil and needs to run first to go elsewhere for a degreasing, not in my garage. then i can find all them parts you guys say are there.

[gmctd]

The fuel line connections are via rubber lines, just connect the tank line to the pump before attaching it to the engine, depress the actuating lever a few times, and you will have primed the pumping chamber.
Connect the line to the filter, open it's drain, give the pump a few more strokes, and it's fully primed.
Takes a little pressure to force the lever, but can be done.

You might also get four or five cans of Autozone Engine Degreaser, in the white cans, and spray down the engine compartment. Hit it with hot water from the bottom tap on your house water heater, and the mess will wash away - the Autozone cleaner turns white when exposed to water, so the neighbors won't complain.
Use one can to clean the floor\driveway afterwards.

jd

[FredM]

thanks i'm degreasing it as i go for now, also this engine has been sitting for a long time, after i prime it what will disconecting the proper wire from the ip do for start up?

[britannic]

Originally posted by FredM:
thanks i'm degreasing it as i go for now, also this engine has been sitting for a long time, after i prime it what will disconecting the proper wire from the ip do for start up? It allows the lift pump to prime the IP and vent air back down the housing return line, without forcing any air into the injector lines, thus preventing a major airlock.