[f100cleveland]

I just got my fuel system installed and I am having a problem with fuel pressure drop. When I first start it up and the engine is cold, it has about 10-11 psi at the Mallory 4309 return regulator. But as the engine heats up, the pressure slowly starts to drop. Once it gets up to temp and everything gets heat soaked, its only putting out about 6.5-7 psi and if the return line gets blocked off, it'll push out about 8 psi. Why is there such a change in fuel pressure as the temps go up? Oh yeah, the fuel pump is an Aeromotive SS 150+ with an Aeromotive dead head style regulator right after the pump set at 12 psi. (My return line isn't quite big enogh and doesn't have enough size to bring all the excess fuel back to the tank at 18-20 psi. I will be putting a bigger return line on it sometime in the near future.)

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1982 F100 - 357c w/ stuffed 4v's and Funnelweb. C-6 trans, Gear Vendors o.d. and 4.86 geared Detroit Locker 9" rear. http://www.supermotors.org/registry/vehicles/detail.php?id=6723

<font size=-1>[ This Message was edited by: f100cleveland on 5/3/06 7:48am ]</font>

 

[FEandGoingBroke]

sounds like the fuel pump is slowing as it warms up, not necessarily the motor....


FE

 

[futuraman]

Measure the voltage at the pump, maybe you're having a voltage drop problem and not getting enough voltage to the pump.

 

[f100cleveland]

*Update*
I went out again and and set the Aeromotive deadhead style regulator up to about 12-13 psi cold. Took the truck out and drove around and got everything warmed up again. Checked pressure again and it was about 7.5-8 psi with the vacuum unhooked from the 4309 regulator and about 5.5-6 psi with it hooked up. If I pinch off the return line, it jumps up to about 11 psi. So I'm hoping that it stays that way now. I'll check it again tomorrow night after work.


I'll check the voltage tomorrow after work and see what its at.

 

[jasonn]

Do you have a fuel pump relay wired in??

 

[f100cleveland]

*2nd Update*

I checked the voltage at the pump, it has the same voltage as the battery. Was about 13.8 volts at idle.

No, I'm not running a relay to the pump yet. It will have a relay as soon as I mount my battery in the rear.

I was informed that liquid filled gauges aren't good to run in an engine compartment. So, I swapped out the liquid filled gauge for a standard one and the pressure fluctuations have disappeared. It stays at the same pressure hot or cold. I'll know for sure tomorrow morning when its in the mid 40s.

Thanks for the thoughts guys.