fuel pump eccentric

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dirty white boy

dirty white boy

50 yr old Juvenal delinquent
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how can you check the fuel pump lobe on cam to be sure its stroking the pump arm fully?? got a high speed fuel delivery issue i trying to figure out!
 
If the pump is within spec (see factory service manual for procedure)

It is working propper.

Try with the fuel cap removed

With a plugged tank vent the high rpm fuel delivery could be compromised.
 
80 model D150 stock /6 od833 step bed, had tank off and cleaned out back in 2019 and replaced fuel lines and pump been running fine every since till this weekend 2 70 mile round trips across southern virgina so my son could see his mother.... bunch of long rolling foot hills truck go to starving for fuel on long pulls at high way speeds, rest of time its smooth as warm butter!!
 
Pull the pump and look for wear on the arm. If the eccentric wore the pump arm also would be wore.

I have seen the pump arm pivot pin on cheap pumps wear and causing your problem. They get loose and lose diaphragm stroke . Switch out the pump with a better brand.

Your problem could be other things

Gas cap not vented
Pin hole in fuel line or hose
Low float level
Bad return filter
Sock on pick up tube pushed to far onto the tube or tube without sock to close to the bottom of tank.

Rarely do you see the eccentric wore that far to effect pump operation without pump noticeable damage to the arm
 
no sock on pick up but its not to close to bottom of tank ether! no return filter or return line on it! vent seems good but will check it this evening as well as line for any issues! its a cheap orillieys pump thay replaced after first one quit after 2 weeks back 5ish years ago, ordered a carter pump off amazon already....DWB!
 
My D-100 had a similar problem, plus after sitting for a few days it did not want to pull fuel up to the carb while cranking (had to manually prime the carb. Turned out to be a very small leak in the fuel line. Would not leak fuel, but would suck air, and the pump would not pull enough fuel. Did not locate the leak. I just replaced the complete fuel line from the tank to the fuel pump.

My 88 diplomat with a 318 had a problem after I replaced a oem pump (broken arm) with a replacement. Car would run ok, untill trying to pass someone on the highway. Then it would run out of fuel just as I got along side of them. Turned out the replacement pump had too much free play in the arm before it would operate the diaphragm. Would not pump enough volume. Every pump I got, even from different stores was the same. I wound up heating the arm and bending it slightly, to take up some of the free movement. That worked good enough. About 2 years later, I got another parts store pump, and it did not have the excessive free play. So installed that pump, and car has been fine, since.
 
took cap off and hit the high way and first good hill it was stumbling so it ant a vaper locked gas cap! raining cats and dogs here today looks like most the week as well....
 
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High mileage slants can have the fuel pump enteric on the cam worn out. There is a good picture of one in Dutra's slantsix book. If you pull the fuel pump you may be able to look at it on a pickup truck.
 
yeah its a thing that dose happen i found threw researching fuel pumps before i made this post! and ill be looking at when i pull pump, got one them camera recorder thingy's on end of a wire kinda like what a dr use's for a colenosterphy.....29.99 on amazon prime with free shipping!!
 
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