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GMC V6 and V12 Engines Engine repair and rebuilding

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  #21  
Old January 31st, 2019, 03:53 PM
Clarke Clarke is offline
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Default Re: 1966 And Later Fuel Pumps

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Originally Posted by ilvracn View Post
i still had my old pump laying on the bench from this summer when it went bad. i decided to take it apart, and see what went wrong. one of the check valves fell out. i was driving at hiway speed, i think the vibration from 3400 rpm probably vibrated the valve from it's seat in the pump. diaphram looked excellent. looks like manufacturer defect, should have been staked in.
Interesting... Did the engine die on the road or did it still run?

The first several that went bad on me, I took apart and they had a small tear in the rubber diaphragm towards the outer edge just inside the body flange. I’m assuming this due to having a hard point/edge that the diaphragm is repeatally flexing against? The pumps still worked with tear, but leaks oil from weep hole and I’m assuming you risk getting gas in the crankcase if you continue driving. Luckily, none have left me stranded.

Thanks for sharing.
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  #22  
Old January 31st, 2019, 05:46 PM
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ilvracn ilvracn is offline
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Default Re: 1966 And Later Fuel Pumps

lost power going up a long hill, pulled the hose off of carb, would still squirt a little gas out. i thought gas gauge was wrong and ran out of gas. a farmer stopped to help, and went and got 5 gal gas. put 4.5 gal in tank, same thing. filled holley carb float bowl from vent hole, got truck running i was able to drive it home. started to run out of fuel in carb again on next hill. backed off of throttle, ran about 1/4 to 1/3 throttle up hill, made it over top of hill. was able to nurse it back, just kept rpm's up and throttle light. i was expecting to have crankcase full of gas but it was ok. changed oil just to make sure and replaced fuel pump.
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  #23  
Old June 17th, 2019, 04:20 PM
zoulas zoulas is offline
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Default Re: 1966 And Later Fuel Pumps

Which fuel pumps are rebuildable? I have been getting the NAPA and they seem rebuildable but I am told there is no rebuild kit. The ethanol gas seems to destroy these pumps.
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  #24  
Old June 21st, 2019, 12:15 PM
Clarke Clarke is offline
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Default Re: 1966 And Later Fuel Pumps

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Originally Posted by zoulas View Post
Which fuel pumps are rebuildable? I have been getting the NAPA and they seem rebuildable but I am told there is no rebuild kit. The ethanol gas seems to destroy these pumps.
Not sure about the rebuild kit, but based on my experience, Ethanol gas has nothing to do (or very little) with premature failure of the rubber diaphragm. You can find detailed explanations to my therory in earlier posts.

In short, the pump arm stroke (travel) is too great for the (smaller) diameter of the pump. I have proven this by using and hauling non-Ethanol gas on many road trips, and by the type of driving. These pumps last a lot longer when cruising around town at low to mid RPM range.

Constant higher RPM is what kills these pumps quicker. I have proven this multiple times by replacing the pump twice within a few hundred miles, running constant highway speed at 3200-3400 RPM while burning non-Ethanol gas (versus driving the same miles back and forth to work through town over a longer period while burning Ethanol gas).

My experience is based putting approx 15,000 miles over the last ten years on my ‘62 305.
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  #25  
Old June 21st, 2019, 03:29 PM
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FetchMeAPepsi FetchMeAPepsi is offline
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Default Re: 1966 And Later Fuel Pumps

Another big killer is drying out. If you use your truck then don't use it for extended periods you can get dry cracks in the diaphragm that keep your pump from being able to generate any pull - or push.
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