No fuel pressure

JGM3E3632

JGM3E3632

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About three weeks ago I notice my E36 M3 was tough to start. Only after it sat for 5 or 6 hours. It is losing fuel pressure some way. I thought it may have been the check valve in the few pump. So I replaced the fuel pump and it made no difference. After the second try the car cranks right up and runs very smooth, the car runs like it is new. I hooked a fuel pressure gauge to the fuel rail and after 3 hours the psi went from 51 psi to 18 psi. These cars are supposed to mantain 28-32 psi when the car is off. I'm thinking it maybe a damaged injector, because if it was leaking from a fuel line you would smell or see feul. Does anyone have any suggestions for this problem? [burnout] [:(!]
 
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SloopJohnB

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No fuel pressure.

I don't have the fuel injection schematic for your E36 but some general comments:
You're right about a check valve being the first place to check. OTOH, I"m not sure a new checkvalve comes with a new fuel pump! Are you?

There are only a couple other places for fuel to leak...a leaking fuel injector would not necessarily smell fuel-y....and if it leaked a lot could theoretically hydraulically lock a cylinder when you tried to start it...especially if the leaking injector leaked into a cylinder near TDC on compression with all valves closed. In any case, a leaking injector is relatively easy to find...just pull the fuel rail with all the injectors attached and run the fuel pressure up to spec and look to see if any of them leak...since you note it leaks down quickly you should be able to spy the leak. This is similar to an injector spray pattern test except you're not cranking the engine or energizing an injector to check spray pattern. OTOH, you might as well check the injector spray pattern now! If it's weak or dribbly, either clean or replace the injectors.

The other place for a fuel system leak is the fuel pressure regulator. In your case it seems unlikely because the car runs well when started.
 
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