I have an odd problem with fuel pressure. First I'll explain my setup:

- '91 RS
- Demon 750CFM Mech Sec Carbed LT4
- Removed stock pump from tank, replaced w/piece of straight tubing
- Holley electric blue pump, mounted near tank
- Holley regulator, as supplied with pump, mounted on fenderwell in engine bay
- rubber lines to the carb
- Autometer fuel pres gauge, measuring pressure at the regulator
- Pressure gauge mounted on firewall, outside, under the hood, where I can see it while driving

With that said, here's the behavior....according to the gauge. I start the car after it's cooled completely down, say after sitting overnight. The pressure is good at about 7lbs, where I intend for it to be. I drive it for about 20 minutes, long enough to bring it up to temp, stop, and shut it off. Say I wait 10 minutes, come back to the car and start it. Now the pressure has dropped to about 3-4lbs, according to the gauge. I take off driving, and gradually the pressure will rise, eventually reaching about 7lbs again.

Seems to me this has something to do with heat soak, but I'm not sure. Is the pump getting soaked? I called Holley and they suggested that I inspect the check valve in the pump. I did, and it's OK, with complete freedom of motion.

Any thoughts? My setup does not currently use a return line. Would a setup using a return line keep the pump cooler, and maybe prevent the problem?

Sorry for the long question. Thanks in advance.... RSR

 

is your pump, regulator, or gauge near a heat source? that may explain things.
Another thing is where the pump gets its power from? is the wire or relay near a heat source?


another thing is that Holley pumps do like to have return lines. Most people get pressure 'creep' without a return line. Deadheading a pump will make it work harder and slightly warmer but shouldn't be causing the problem.
I deadhead my carters and they have no problem with it.

 

The pump is mounted on the wall directly behind the rear seats, on the side of the car opposite the exhaust. I don't think it gets too awfully hot. The regulator is on the fender well in the engine bay, so it gets some heat. The gauge is on top of the firewall, and the line to the gauge runs over the engine. I can understand how a warm pump may lose pumping power, but I'm not sure I understand how a warm regulator or gauge could cause the problem.

The wire to the pump doesn't get very hot with my configuration.

The pump is mounted at a slight angle.....?

Still searchin'.......

 

many regulators & gauges have springs inside them. Springs are always affected by heat. That's why I mentioned that.
I'm not sure what it is but you could always try another pump to see if the problem remains.