fuel pump pressure ?

Perfromance and Technical discussions about C3 Corvettes
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Tell us about your Corvette: 1968 327/350 just out of 20 years storage. starting the process of restoring what I can (not frame off).

fuel pump pressure ?

Post by greggome »

I have been unable to locate factory specs for a 327/350 68' fuel pump pressure and volume with stock Q Jet. I am running only 2 psi with a pump I replaced about a year ago. Volume is good but pressure seems low. anyone know the correct specs on this.
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Tell us about your Corvette: 2001 Targa Top Coupe, Stock 350/350 hp Automatic,
1968 Full Custom Mako Shark Convertible, 454/425 hp, Muncie M20 Transmission. 1965 HP Resto-Mod Coupe, 350/390 hp, Kiesler 5-Speed, FiTech FI, Hedman headers, Edelbrock heads, Comp Cam.
Location: Pinellas Park, Florida

Re: fuel pump pressure ?

Post by rbryce1 »

Depends on where you are measuring it. Out of the fuel pump should be about 7 psi. If you have an in-line fuel filter, it should be about 5 psi between the filter and the carb. If it is lower that that, look for a clogged in-line fuel filter.

If you don't have an in-line fuel filter and are measuring it between the fuel pump and the carburettor, you may have a fuel pump problem. If it is a diaphram fuel pump, it should have a small hole in the upper body. If it does and fuel is coming from it, you have 2 problems, a broken fuel pump diaphram and fuel going into your oil. I lost an engine on the highway in my very old 1961 Chevy Impala because of that. Started knocking then threw a rod. Real Bummer!

Gas in the oil is not easy to find because it evaporates in hot oil so you don't see it or smell it, but it does thin the oil and prevent proper lubrication. Not sure if it does this with synthetic oils. If you don't have the hole in your fuel pump and can't find anything else, I would replace the pump. They are far less expensive than engines.

On a better side, it could also be the pressure regulator in the fuel pump not controlling the pressure. All it consists of is a spring and a ball to relieve the pressure back to the suction side of the diaphram. If the spring weakens and opens before it should or if the ball doesn't seat properly, this can also occur to lower your fuel pressure. Again, replace the pump.

If you don't think it is a broken diaphram and it is running fine with 2 psi, leave it alone until you have fuel delivery problems.
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