GKK

What is the best way to check fuel pressure leak down on my 91 Vette?

With engine on, fuel rail pressure is 42psi but, with engine off the pressure drops to 20psi in about 2 minutes. Would pinching off the fuel return line after starting the engine and then shutting off the engine, determine if the injectors are leaking?

New Racetronix stock replacement fuel pump, 2 year old Bosch III injectors and new fuel pressure regulator diaphragm.





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Cliff Harris

There is a fuel bypass valve in the fuel pump that sometimes leaks. To test that you do the leakdown test but pinch off the SUPPLY line.

Just because you replaced the fuel pressure regulator diaphragm doesn't mean it is not leaking. Pull off the vacuum line while the system is under pressure and see if fuel comes out of the FPR.

GKK

I pulled the fuel regulator vacuum line off and found no fuel.

I'll pinch off the fuel supply line next.

383vett

I wouldn't worry about it. Mine drops to zero in 10 seconds and runs fine.

GKK

Yes, the engine runs fine but, after reading all the posts about, "My fuel pressure holds for hours", I began to wonder if there was something wrong?...

GKK

Fuel pressure reads, 42psi with the FPR vacuum line removed engine running and 32psi with the vacuum line attached engine running.

The fuel pressure still bleeds down with either the fuel supply or return lines pinched off. Does this indicate leaking fuel injectors?...

MrWillys

Does it leak down with both pinched off at the same time? If so, yes it must be leaking at the injectors. Pump it up and pinch the supply, and watch.

hooked073

GGK I have never seen this to be a issue unless the injectors are leaking dowm.

383vett

It could simply be the fuel pump check valve which won't hurt anything. That's where my fuel pressure is going.

hooked073

I agree 383 I have seen people chasethis for days and the fact is unless you have an injector leaking I have never seen this to be a problem.

GKK

It must be the fuel injectors because I've installed two fuel pumps with the same results.

MrWillys

If both return and supply are pinched it can only be regulator or injectors. So, no fuel from regulator and still leaking down leaves only one thing.

l98tpi

Mine drops too, maybe not in ten secs but does bleed off pretty quick after turning key off.

383vett

Pull the injectors out of the manifold while still attached to the rails. Turn the key on and see if any leak.

GKK

I really don't think there's a problem because the engine starts, idles smooth and performs fine!...

I'll call Jon Banner tomorrow about the Bosch III's.



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Klyde

Unless you have all the original fuel injector clips installed do not pull the rail and pressurize it. The 40 psi will blow any none clipped injectors out and flood the engine bay quite quickly with raw gas. I have after market ones from FIC and they are not attached in any way to the rail.