Car is running again but fuel pressure won't come down

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Bob Avellar

Member
Joined
May 25, 2001
Messages
368
Just got my motor running today-Woo HOO!!Used 8 AN fuel feed line (1/2") attached to the steel line at the pump hanger in the tank. Used 5/16" steel vent line. Used a shorty 90 degree Earls fitting under the fuel pressure regulator 1/4" I think to a 6AN return line (3/8") which connects back to the steel pump line at the tank.
This is what happens:
With the pump running for a few seconds at startup and then again after engine shutdown I can set the pressure to 45psi. I can adjust this pressure (with pump not running) way down if I want to. However when the pump is running continuously like when the car is running I can't get the pressure below 70psi! As soon as I shut the motor and pump off the pressure will go back to whatever I set it for-like 45. Putting the vacume line on the reg has no effect. I tend to think that somehow there is a restriction in the return line (but I can't see how). My guess is that when the pump is flowing the regulator can't bypass enough fuel to lower the pressure but it works fine and is adjustable when the pump shuts off. Anybody encounter this before? I plan to disconnect the return line tomorrow and blow air throgh it to see if it is restricted or not. I never had a problem with this regulator before right up to the point where I took out the motor so I don't think it is the culprit unless something got in it and is blocking it from working. Just looking for some hints, past experiences or troubleshooting procedures to try. God it was great to hear her running again after over a year!!!! Today was a very good day!!
 
First thing is congrats on getting her fired up!!!!!

As far as the new problem the only thing I can think of is a clog in the return line.Dont know how long the car has been siting but it might have just gone bad(AFPR).

good luck keep us posted.

John
 
If your return line is not clogged and your fuel regulator is working okay then perhaps this problem could be because of the bigger fuel feed line. Due to the bigger fuel line and the greater volume of fuel that is being displaced by the fuel pump it could be that now the return line is not bleeding off enough fuel so that the regulator can throttle down the fuel pressure.

You might have to reinstall your stock fuel lines to see if this is your problem.

Just a thought!
 
A -6AN return line is more than large enough.

There is a good chance you have a restriction in the return system or a punched FPR.
 
The return is restricted somewhere. With the engine running the fuel pump receives additional voltage and as a result an increase in fuel flow. This will be worsened if your running a hotwire from the back of the alternator. Something downstream of the regulator is providing a restriction. Are you using a 340 fuel pump? How did you attach the 90 deg. fitting to the bottom of the regulator? The stock o-ring connection under the regulator to the return line has a very small inside dia. and should be cut off in your case. If you suspect something got into the return line then try blowing through the return from the fuel tank end.
 
Problem solved. It turned out that I had the return line trying to enter the tank through the vent! The vent and return lines were mixed up. Swapped them to the correct locations and all is well. Thanks guys. Still a few electrical gremlins to sort out but all the engine controls are functioning fine.
 
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