Jdukes10

I have a 78' corvette and my fuel pressure drops lower and lower as my car runs and it will finally just stall itself out after about 15 - 20 minutes. It starts off at around 7.5 to 8 lbs per foot ( I think thats the right unit for fuel pressure) and right before it cuts off it will be around 5.5 lbs per foot. I am by no means a mechanic but I am learning something new everyday. I believe I have narrowed my problem down to either the fuel filter or the actual fuel pump itself. If anyone has been through the same problem any helpful insight would be much appreciated. Also it doesn't have the stock motor in it anymore, it has a 454 in it now, but I don't think that would cause any of these issues.

BKbroiler

As for the pressure units, it's psi, pounds per square inch. As for your problem, we need more info. What happens at wide open throttle, what type of pump is it, elec or mech etc.

gcusmano74

I wonder if you have a tank venting problem. Try popping the gas cap open when the pressure starts to drop, and see if that improves things.(Obviously, don't drive it like that, just idle it while parked.)

Jdukes10

It is a mech fuel pump and it is fine anywhere from being wide open to just barely being on the gas, it only cuts off when it is at idle. I will give the gas cap test a try right now.

Matt Gruber

does it have a fuel return line hooked up? they often get vapor lock without it.

lars

I don't think the fuel pressure is your problem. The car will run just fine with fuel pressure down as low as 2.5 psi. Most cars run around 3.5 psi. 8 psi is too much, and you'll likely have flooding issues with the pressure that high - the Q-Jet doesn't like pressure over 7. No way will the engine quit with fuel pressure at 5.5. You have other issues.

Lars

Brcmpbl

This is a cold stab, but check the condition and position of the rubber fuel lines from the frame to the pump. I had this problem with my 70 recently and I found it was caused primarily by my having used a piece of bulk fuel line for the inlet hose when I replaced my fuel pump and lines, rather than the formed S-shaped line that can be had from repro shops like Corvette Central and others. I had cut the bulk hose too long and it was pressing up against the upper control arm / shock mount...my motor mounts were also in bad shape so I may have had some very slight movement that was compounding the issue on steep grades and hard braking. In any case, I replaced both the mounts and the installed the proper inlet hose and my problem went away. I can even run my AC at idle now without the car stalling!

Other than that, maybe your timing is off or you've got an ignition issue somewhere.

mysixtynine

What kind of gauge are you using to determine the pressure? Is it liquid filled.

I recently shot a bug with my buddies car he just installed a 454, new engine to him, new hei distributor, new fuel pump and gauge in a car he never drove. So we where about as at step one as we could be.

The engine started fine had about 6-7 psi on the gauge and when it would warm up the pressure would drop to almost nothing keep running then start sputtering and die when fully hot. But it seemed to run on almost no pressure for a while.

We thought it was fuel pressure or vapor lock issues as their are no return lines on his setup.

Turns out that some fluid filled gauges like the jegs ones are only good to tell pressure when the engine is cool. When they warm up they show almost no pressure. (got that from jegs themselves)

Turns out the cheap ignition module in his new HEI distributor was crap. Got a new 1 and the engine runs fine even with the pressure eventually showing almost zero on the liquid filled gauge.

Cant imagine the use of a gauge that goes to zero or just off when its warm....what is the use of that.

Jdukes10

I tried venting the gas cap and nothing changed. I have a gauge on the fuel line that goes into my carburator.