Thread: 302 fuel pump eccentric

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Are these prone to breaking? Car ran fine then no fuel to carb. Feels like eccentric is turning freely in timing cover. common problem?

I wouldn't say common. Out of the millions on the road, I've only known of 1 that had a problem, to a guy that used to be on here.

I've seen more fuel pumps fail than the eccentric. But others will offer their opinions too. Can you shine a light inside and with a mirror look and see if the eccentric is moving while someone spins the motor over with the starter?

I have seen Chevy's cam eccentric go bad but not very often the cure was always an electric fuel pump

If I remembered right, the one that failed on 1 of our members, was a stamped unit and it has a tang off of it that fits into the cam to provide positive rotation. His had the tang break I think, the stronger one has a hardened pin instead of the stamped tang.

The downside in proving this, is you must pull the timing chain cover.

I remembered the long discussion by DaveW but not the details of what he found so I did a search and was amazed that it WORKED!!

Here's a link to the post where he showed a picture of the stamped steel eccentric with the little tab broken off - Embarrassing trip today

Sure wish DaveW would come back.....

there are two different eccentrics used---one is one piece and the other two pieces--the 2 pc one outer portion will/should rotate freely---


you need to remove the front cover to insure that its not caused by loose bolt in the camshaft--------

Thanks guy's. Checked all other possibilities, glogged lines etc. can only assume it's time to pull the cover.
Even the brand new fuel pump arm did not show any wear marks after cranking the engine for awhile.
New to the forum and loving it already, thanks again.

Glad you enjoying it here! We enjoy seeing you! Once you've gone past the "trial period" (10 posts reportedly) and we get to know you aren't a spammer, feel free to share some pics. I'm hoping that ailing SBF is in your avatar vehicle..

If you need a eccentric, I may have a good used one if you want it.

Maybe you can help me with the diagnosis. I can get a fingertip on the eccentric and it does turn but there does not appear to be any slop in it. I have tried the pump hooked directly to a gas can but still no suction.
Any ideas?

1. blow backwards thru the fuel line to make sure line isn't plugged ( maybe first pressurize tank to see if fuel flows forward, then blow backwards if it doesn't)

Originally Posted by jerry clayton

1. blow backwards thru the fuel line to make sure line isn't plugged ( maybe first pressurize tank to see if fuel flows forward, then blow backwards if it doesn't)

Jerry's on target to check the line. A friend having trouble with fuel supply replaced the in-tank pump only to find that his braided SS line from tank to engine was "weeping" along the length, so he replaced all of the line and rebuilt the carb. Ethanol had done a job on all the flexible parts.

big question is, should the outer eccentric turn with my fingertip if it is a 2 piece?

read post #6

Originally Posted by mreed1

big question is, should the outer eccentric turn with my fingertip if it is a 2 piece?

"IF" it is 2 piece then yes, the outside should turn easily. If you have the pump "in your hand", you can move the arm and verify the pump suction and discharge ports. If they work, then it's either the supply side has a hole and it's sucking in air, not fuel or there is a blockage either in a pickup sock or ???

That's why you also need to verify the line can move fluid. Remove the gas cap and blow back into the tank and then add a small amount of pressure into the tank and see if fuel comes out. If that works, and the pump works... then the eccentric probably has an issue.

mreed1, you don't say if this is an engine that's been fine for a long time, and all of a sudden developed this problem or if there were changes made to the engine, and now you've got a problem. One thing I've seen mentioned is that many of the 5.0's were EFI, and when converted to a carb the eccentric is added but the pin in the cam is not changed. The pin for the mechanical fuel pump application is about 3/16" longer to extend out well past the surface of the eccentric. If the shorter pin was left in there it's common for the eccentric to "jump" the pin and cause loss of fuel, and it may "grab" occasionally making it a sporadic problem.