Lift pump question...

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braol

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Apr 16, 2014
348
Hunter 27 Rebel 16 Great Lakes Naval Base, IL
If a lift pump isn't developing sufficient pressure, will that cause the injector pump to not work?

I am getting fuel through my lines from the lift pump but my injector pump isn't developing any pressure. I didn't know if the 110-12psi of "head pressure" was required to get a good boost from the injection pump or not. Again, the lift pump appears to move fuel through the lines, but was concerned that maybe it isn't developing sufficient pressure....
 
kloudie1

kloudie1

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Nov 6, 2006
10,212
Hunter 34 Mandeville Louisiana
The lift pump discharge pressure is very low, 1.4 PSI for the GM series. Not sure about the QM, but normally less than 5 PSI.. usually, if you have fuel flowing, that is sufficient. Note that on a tractor, the injector pump on this same engine is fed by gravity from the tank being only a foot or so above the pump (<0.5 PSI).. Two things to verify.. all air out of the lines feeding the injector pump.. bleed at the (delicate and easy to strip co-axial bleed screw) fuel inlet to the injection pump until no bubbles come out, only liquid fuel; make sure that the fuel cutoff lever is fully "ON" and the pull-to-kill wire hasn't slipped and is leaving the lever in the kill position. Some QM didn't have a kill knob, yours might.
 
B

braol

.
Apr 16, 2014
348
Hunter 27 Rebel 16 Great Lakes Naval Base, IL
I have verified fuel at the injection pump. Fully bled. I get fuel to 'squirt' up in the air when I remove the check valve at the injection pump outlet...but with the valve installed I get nothing....maybe a little seepage is all. Again, I've verified fuel moving out of the lift pump. I can bleed all the lines from the tank all the way to the injection pump without a problem.
I also only get injector pump noises (the tell-tale squeaking) when the governor is in the fully seated position (ie, max throttle). I think the governor spring behind the needle valve is had it. I've verified that the needle is seated before assembly, but the spring looked a little "sprung."
 
C

Capt jgw

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Feb 8, 2014
1,300
Columbia 36 Muskegon
Sounds like you already have it figured out. If the Governor springs are worn out, it's not going to run. Probably the fuel rack is not opening, or there's some other injection problem.
 
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Benny17441

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May 24, 2004
7,213
CC 30 South Florida
Sounds like you may still have some gummed up components in the high pressure pump. Pressure should be steady.
 
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