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-   -   Chevy mechanical fuel pump moving TOO MUCH fuel? (http://www.hotrodders.com/forum/chevy-mechanical-fuel-pump-moving-too-much-fuel-208140.html)

Torque454 11-03-2011 11:57 PM

Chevy mechanical fuel pump moving TOO MUCH fuel?
 
Have a 79 C-10 chevy that I put a 454 and TH400 into, in front of a 14 bolt full floating 4.10 axle.

Everything is solid and dependable as can be EXCEPT something to do with the fuel pump. The problem I am having is that at random, this engine floods like you wouldnt believe. Its like the fuel pump is moving more fuel than even that old big block could ever use. I'm shocked the engine didnt hydrolock. Whats even more wierd is that it is totally random. It was fine for a few months after I put this new fuel pump on it, and then one day it just started flooding like crazy. I pulled the carb apart and there were no obvious problems. I lowered the float a little to see if that helped and it didnt. Then I installed a new float. Still didnt help. Needle and seat are practically new, and are clean.

Finally it stopped flooding. I let it sit since I dont drive it a whole lot. Jumped in it a few weeks later and its flooding more than ever. I tried everything to get it to stop flooding and it wont. Fuel pressure is 6.5 PSI.

I finally decided to plumb a low pressure fuel pressure regulator into the system between the pump and the carb. Had to turn the regulator down ALL THE WAY to get it to stop flooding. That fixed it I thought. also installed a clear fuel filter between the pump and the regulator. Filter filled up 90% of the way with fuel. Everything was going great. Took off in the truck to get some more gas. Ran great up to the station, but as I left, it began acting like it was running out of gas. Pulled over to the side of the road and the fuel filter was low on fuel. I turned the regulator up a little and magically the truck started running perfect again. Took off, went to do what I took the truck out to do (unload trash at the waste dropoff facility) and left it idling the whole time. Got back in the truck, and started to take off and once again it acted like it was running out of fuel. It would idle but thats it. Got out and turned the regulator up some more and it started idling even better. Took off, nailed the throttle to the floor up a hill and it was just fine. Got home without any problems.

BTW each time I turned up the regulator, you could start seeing fuel begin filling the filter up again.

Its like when i left home, the fuel pump was pumping WAY WAY Too much fuel. And then when I left the gas station, it was pumping less than what it had been, thus the reason I had to turn the regulator up a little. And then again after dumping trash I had to turn it up even more, because the little bit I had turned it up at the gas station was no longer enough. The pump had obviously lowered its output again.

What the world is happening? I didnt know a mechanical fuel pump could ever pump TOO MUCH fuel, let alone randomly choose when it wanted to pump too much and when it didnt. Its just a stock replacement carter fuel pump from the parts store - nothing special - no high performance pump or anything.

BTW I never have any luck with NEW mechanical fuel pumps. For some reason, every time I have an OLD mechanical fuel pump fail (which isnt often - they are dependable as ever) the new ones never work or never work right - such as the case with this one. I always end up with electric pumps. I dont understand this either. Do companies not make good mechanical fuel pumps anymore?

I dont know what to do next. The pump is obviously the problem. I guess I should replace it? But IDK, it pumps plenty of fuel and pressure... in fact too much, at times, and just enough at other times. Makes no sense to me at all. Generally when something fails... it just stops working or stops working well enough. But not this time. Its working TOO well...

DoubleVision 11-04-2011 01:48 AM

Did you lube the pump cavity upon installation? Most don`t and this results in problems. Once I had a problem like yours, and I kept on chasing this problem for months, massive flooding problems. It turned out the vapour line from the fuel tank I plugged off, the tank couldn`t breathe so it was forming air pressure in the tank and forcing the fuel out of the only outlet it had, which was the fuel line going to the carb itself. One day I drove it and it seemed okay, I put $13.00 in gas in, got it in the next day to find it sitting on empty. After I shut it down the pressure build up caused it to force the fuel out of the boosters which filled the oil pan with about 3 gallons of gas. I was so ticked off at it I almost put a match to it.
However, set your fuel pressure at 4.5 psi. The test drive. You shouldn`t have any more issues. I don`t know what carb your using, but Edelbrocks and quadrajets don`t like anything over 5 psi. Some Holley`s and demons can use up to 9 psi, but all the ones I`ve used couldn`t use over 5.5 psi which is why I run it at 4.5 psi as I don`t like running it up to the borderline.
I don`t know about big block chevy`s, but small blocks don`t have a direct oil to the fuel pump, it simply gets oil that runs off the cam. Many install a new pump and don`t pack the cavity with lube which causes the pump to overheat which causes problems. If you didn`t lube your pump you may want to do so now. After you set the fuel pressure to 4.5 psi, check the float level and set it if needed.


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