M38A1 fuel pump question
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- G-Master Sergeant
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M38A1 fuel pump question
A year ago, i bought a rebuild kit for my M38A1.......Seems that the newer type checkvalves are not too good. The original ones were brass and of a different configuration. New ones are aluminum and not configured the same. Think perhaps that i use my jeep semi regurlarly, one would surmise that the ethanol wouldnt be any issue. Fuel tank was loaded with old fuel gum, that i did my best to clean out, and for a year and a half everything worked just fine. Now, it wont pump at all. Have had it off and apart 3 times in the last couple days, and can not find anything that would raise an eyebrow. Tank filter is original, but in good shape {checked it today} , lines are clear, but still no fuel being pumped. Call me stumped.
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Re: M38A1 fuel pump question
This is one of those slap your forehead things but is the fuel shutoff valve open? Can you suck fuel from the tank through the fuel line? Is the flexible fuel line kinked or constricted in any way - if it is an older line, gasohol may have swelled the rubber. If the pump sucks and the tank has gas in it, the problem may lay in between somewhere.
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Re: M38A1 fuel pump question
Wish i could say it was that {shut off valve}..........it sucks that it just wont suck. Cam is good, actuaiting arm is just slightly polished, diaphrams are new {less than a year}.......wish i had saved the old checkvalves. i've had the darn thing off and apart 4 times on sunday, and still no resolve. Had the tank / fuel access of as well, and all is good. I am thinking it literally has to be those aluminum ckeckvalves. Thinking i will supply it with an electric fuel pump at this point, though hate the thought of having anything not meant to be there. Having enough issues with all the bubba holes from rollbar and non issue canvas snap holes.
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Re: M38A1 fuel pump question
First thing you need to do is prove that the fuel pump is the problem. It may not be & can be easily eliminated..
Get a vacuum gauge from HF for $15 [it will be good for other things later on] & see if the pump is pulling a vacuum @ the fuel pump inlet. If it is then the fuel pump is not the issue.
The fuel pump relies on air pressure [14.7psi] differential on top of the fuel in the tank to flow to the fuel pump.
The fuel pump creates a lower pressure, commonly referred to as vacuum.
Anything air leak between the fuel tank pickup & the fuel pump inlet, including any flex hose/s, can stop fuel delivery to the pump & will not show up as a fuel leak.
Get a vacuum gauge from HF for $15 [it will be good for other things later on] & see if the pump is pulling a vacuum @ the fuel pump inlet. If it is then the fuel pump is not the issue.
The fuel pump relies on air pressure [14.7psi] differential on top of the fuel in the tank to flow to the fuel pump.
The fuel pump creates a lower pressure, commonly referred to as vacuum.
Anything air leak between the fuel tank pickup & the fuel pump inlet, including any flex hose/s, can stop fuel delivery to the pump & will not show up as a fuel leak.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.
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