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Discussion Starter · #1 ·
I'm seeing 20 psi at the fuel rail on my SL with the motor off. When I start the motor it jumps to 65 psi and then as soon as I shut off the motor it immediately drops back to 20 psi. I figured the FPR was bad so I replaced it with a used spare that I had but it is still doing the same thing. I am thinking that the spare that I put in is also bad but it is strange that it has exactly the same pressure readings as the original FPR. Could anything but the FPR cause this? Thanks, David
 

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there is 4 issues that can do this. One is obvious a leak fuel line, a pressure regulator that is either has a leaking diaphram or is leaking the pressure back to the tank. Leaking fuel injectors and the last and my vans favorite is a bad one way check valve in the fuel pump.

It easy to check. You will need a helper and some needle nose vice gripes. Adjust the vice grips to just be able to pinch a fuel line closed but not damage it. Have someone keep cycling the key on off on off to keep the pump cycling with the engine off. Now pinch off the line going into the rail and have the helper stop at or close to the time you pinch it. Now watch pressure. If it stops dropping its your check valve in the pump. If it doesn't it may be the regulator or injectors.

Now lets do it again but this time just pinch off the return line and cycle the key. Pressure will be higher then normal but thats ok. Just watch the pressure. If it stops dropping off its the regulator. If it doesn't its either the pump check valve or injectors.

Now leave the one on the return line and have your helper cycle the key again like before and pinch the feed line again. Again have the helper stop about the same time you pinch the line. If the pressure still drops off and there wasn't any signs of fuel leaking out the vacuum line portof the regulator like someone else posted to check its your injectors.
Tim
 

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Discussion Starter · #6 ·
Thanks, I hadn't had a chance to work on it again until today. My fuel pressure didn't seem normal with the "new " used fuel pressure regulator. I was reading no pressure with the key off and 65 PSI with the engine running with and without the vacuum hooked up. When I pinched off the return line I was still reading 65 PSI and when I pinched off the pressure line the pressure would still drop to zero when I shut off the motor. I swapped the regulator a second time and now I am getting 55PSI static and 45PSI with vacuum connected. Also, when I pinch the return line the pressure jumps to over 100 PSI. However, when I shut off the motor the pressure still immediately drops to zero. I tried pinching the pressure line and it still drops. Could it be the check valve in the fuel pump? Thanks for your help. David
 
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