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Hi. I've had a fuel leak near the pump of my 79 F150 with a 400 for some time. I didn't know exactly where it was coiming from, but fuel was being sprayed on to the oil filter from something near the pump. I assumed it was the steel line, and that it had rusted through or cracked, and was going to replace it when I had a chance. I was poking around today though, and realized that the fuel was not leaking from the line, but from a hole in the side of the mechanical pump. For someone who knows what these pumps look like, there is a horizontal cylindrical bump out near the top of the pump, on the side of the pump that is away from the engine. The fuel is spraying in a mist out of one side of that. To me, it always seemed to be a screw channel, but I didn't think the pump was 2 halves put together?
If anyone can tell me more about my pump, what that bumped out section is, or why/how fuel could be spraying out of it, I would very much appreciate it. A new pump is cheap, but if a screw in there has just come loose I don't want to waste the money,
Thanks for any help, AleX
OK. I put a good sized 4 barrel (i think 700 cfm) on what had been a 2 barrel carbed engine all it's life, could I have overdrawn the fuel pump and broken it? Is there such a thing as overdrawing?
And if I did overdraw (or even just now that I hav a 4 bbl), should I upgrade to a high flow pump?
AleX
I know this is a 10-year-old post, but I thought I would add my own experience, since this helped me understand why my own pump went bad.
Had a full tank on my 1979 F-100 (302) and parked in on a slight downhill. Woke up to the smell of gas and a dribbling fuel pump, from the breather/weep hole. Starting the engine meant fuel squirting all over my oil filter.
Changed the pump (from a Delphi MF0094 to a NAPA pump), engine fired up after maybe a 12 cranks. Was downhill, so had effortless priming.
I wanted to identify the failure, so I decided to take the old pump apart after running water through it (that thing is a pipe bomb basically and the angle grinder is the fuse!).
Basically, a small wear point occurred, enough to make a pinhole through the diaphragm, and enough to cause the problems above. It happened right where the diaphragm is held down by the pump's pressed flange.
I don't think I would have noticed had I not parked downhill.
Attaching pics of the pump disassembled and of the hole.
Thanks!
Last edited by ManiwakiF100; Apr 25, 2021 at 04:01 PM.
Reason: Removed an emoji
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