Fuel pressure dropping - Team Camaro Tech
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post #1 of 11 (permalink) Old Mar 28th, 11, 03:36 PM Thread Starter
 
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Fuel pressure dropping

I have a 68 Camaro with a mild 350. I am running a Holley black electric pump through a Holley pressure regulator to a 750 double pumper. When I start it up cold, the pressure is at 9 psi and as it warms up, it drops gradually to 6 psi. Is this normal? Should the pressure be the same all the time? Should I change to a bypass regulator and run a return to the tank? I am confused. Any help is appreciated.
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post #2 of 11 (permalink) Old Mar 28th, 11, 03:41 PM
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Re: fuel pressure dropping

when was the last time you checked your fuel filter?

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post #3 of 11 (permalink) Old Mar 28th, 11, 03:49 PM
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Re: fuel pressure dropping

9psi is on the high side (Holley calls for 7-7.5.....and no, it should not be dropping.

Have you checked the diaphram in the regulator ?

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post #4 of 11 (permalink) Old Mar 28th, 11, 03:57 PM Thread Starter
 
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Re: fuel pressure dropping

Yes, I just changed both filters. I haven't done anything with the regulator. Is there any visual signs that the diaphram is bad? Or just by the gauge dropping? It is about 5 years old with about 2000 miles on it. Mabey it went bad from lack of use?
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post #5 of 11 (permalink) Old Mar 28th, 11, 04:31 PM
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Re: fuel pressure dropping

Double check your gauge as I chased a similar problem only to find out it was the liquid filled guage changing with temperture.

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post #6 of 11 (permalink) Old Mar 28th, 11, 04:44 PM Thread Starter
 
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Re: fuel pressure dropping

How did you solve that problem? Just set it at operaring temperature? Move the gauge?
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post #7 of 11 (permalink) Old Mar 28th, 11, 06:41 PM
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Re: fuel pressure dropping

Replaced the oil filled guage with a holley gauge. It's been right on since then...6 1/2 psi.

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post #8 of 11 (permalink) Old Mar 28th, 11, 07:09 PM Thread Starter
 
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Re: fuel pressure dropping

I have a Russell gauge that came with the carb lines. I would think it is a good one too. I guess i'll try replacing the diaphram first and go from there. Anyone else have any other ideas?
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post #9 of 11 (permalink) Old Mar 28th, 11, 08:28 PM
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Re: fuel pressure dropping

My problem was the same as yours, pressure reading dropped as the engine reached temperature.
Verified fuel pressure with an other gauge, mac tools.
My gauge mounted near the carb was the problem, fuel pressure was constant and correct.
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post #10 of 11 (permalink) Old Mar 29th, 11, 03:37 AM
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Re: fuel pressure dropping

As suggested, remote mount the gauge, get it away from the heat and vibration.
Use copper tubing, no plastic tubing. See your local neighborhood HVAC tech, he'll have some. Be sure to bleed the line for a more correct reading.

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post #11 of 11 (permalink) Old Mar 29th, 11, 03:57 PM Thread Starter
 
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Re: Fuel pressure dropping

Took it out for the first time this year. I adjusted the regulator cold. As it warmed up in the driveway, the gauge dropped like before. took it out for a drive and had no drivability problems. I even hammered it through all the gears and still no problem. When I got back home, I popped the hood and checked the gauge. The pressure was at 6.5 compared to 7 when I started it cold. Looks like it is a heat issue when standing still and idling. The fuel lines and regulator were cool to the touch. Not like when idling. I am thinking about changing to a bypass regulator and running a return to the tank so the fuel is allways moving therefore staying cooler. It should be easier on the fuel pump too.
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