This is topic Fuel Pump Question (mechanical) in forum Tech Talk at Northern California Ford Owners  .


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Posted by Wolfie351 (Member # 651) on :
 
Here's the whole story...my '85 Mustang (carbed 351W) started to get some significant hesitation off the line. It was about time for some regular maitenance anyways so I changed plugs, wires, cap, rotor, fuel filter, etc. The hesitation only got worse and now it even feels like it's missing. Yes, double checked everything...no vacuum leaks and plug wires are correct. Changed to a known working carb from my '70 Torino, that didn't help. I threw on a fuel pressure guage to go through the process of elimination and something interesting happened. When it's cold and I start it up, it reads 6 psi. After the engine has warmed up, it slowly starts dropping to where it reads 0 psi. The float bowls on the carb dont drain and the car continues to run, although badly. Would a bad fuel pump act this way. Would a car continue to run with 0 psi fuel pressure? I'm also suspecting a head gasket leak, compression test results to follow soon. Any thoughts on this will be appreciated, thanks in advance!

Scott
 
Posted by shade-tree (Member # 298) on :
 
those are almost exactly the same symptoms of my flagging mechanical oil pump in my previous 302 shortblock, ran fine on startup, over time, it would get near zero pressure. However, I could 'rev' the motor to get pressure up. Does that work with your fuel pressure? revving brings it up?
 
Posted by Wolfie351 (Member # 651) on :
 
No increase in psi when I gun the throttle, but I'll tach it up to a couple thousand RPMs and check.
 
Posted by BIGJUNE (Member # 1716) on :
 
sup man sounds like a bad fuel pump . change it .try flooring it up a hill ,if it hesitates or lags its the pump.
 
Posted by Wolfie351 (Member # 651) on :
 
Changed out the fuel pump and I still have the same slow drop in fuel pressure as my engine warms up. Maybe vapor lock? If so, why now all of a sudden? Hell, maybe I have a bad gas cap. Maybe I got a bad batch of gas. Any and all suggestions appreciated!!!
 
Posted by street_illegal_stang (Member # 1554) on :
 
check your carb.
 
Posted by Wolfie351 (Member # 651) on :
 
quote:
Originally posted by street_illegal_stang:
check your carb.
Yeah, that's usually the culprit, but I had already switched to a known working carb before I changed out the fuel pump. In fact, I tried my stock Holley 4180, a 750dp from my Torino and a 670 Holley Street Avenger
 




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