Bimmerfest - BMW Forums - View Single Post - Where is the M54 fuel line schrader valve (to test lean conditions fuel pressure)?
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Old 12-30-2012, 06:44 PM
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This thread today has a bunch of good questions for those testing fuel pressure:
> E39 (1997 - 2003) > Question on Fuel Pressure Test / Diagnostic

Originally Posted by samdayo View Post
Having a non-start issue and wanted to ask some general questions as I've looked at a lot of threads and youtube videos but there doesn't seem one to help me answer my questions.

I'm hoping someone who has done a fuel pressure test on an E39 / M54 can confirm a possible bad pump.

Thanks in advance. I'm using the Actron fuel pressure tester cp9220a featured on Bluebee thread on finding the Schrader test valve. By the way, the adapter on my kit did not fit the rail valve well without a slight modification to the brass fitting. It would leak at the adapter because it would not thread all the way down due to the collar on the Schrader value.

Question : I've read the fuel rail is under pressure but when I first installed the tester, it was at 0 psi. Is that the case? Car has been sitting for 1 week due to non start. I'm assuming 0 is normal but I keep reading warnings about it should already be pressurized.

I can hear my fuel pump prime for 2 seconds each time I put key to 'on' position or second position.

Question : Does key to 'on' position increase the fuel pressure up to 48 psi immediately or does it take time to build up? I've watched some youtube videos but everyone likes to cut to the car running state instead of showing you what happens when key to 'on' position.

In my situation, the first time I put key to 'on' position, psi went up to 10 and I watched it climb to a little more in the next 20 seconds. It probably went up to 13-14 psi. My car is currently in a no-start situation and the most I can do is cycle the key to the 'on' position and keep priming my fuel pump. After about 3 or 4 key to 'on' position, the psi is around 40. I had to cycle the fuel pump (2 second priming each time) about 8 times to build up to 45-48 psi. Once I built up the pressure, it holds it.

Question : Is this normal or should it jump up to around 48 psi the first time the fuel pump is primed?

To remove the fuel pressure tester, I had to depressurize the rail by holding a button on the tester and dumping the fuel out. Of course, psi went back to 0.

Thanks for helping me understand the testing better. I appreciate your responses.

By the way, if anyone has a good link to test for spark on an E39 or M54 engine, please send it my way. The best I've found is to remove the coil and spark plug and then ground the spark plug and try starting the car to watch for spark. Any other ways to confirm spark?
Originally Posted by Makomagnet View Post
Samdayo the FP should come up to ~42 psi within about 2 seconds of turning the key to pos 2.

There is a spec for how long it holds pressure (pressure drop) but in 1 week I would expect the pressure to drop to zero.

Also the FP valve is a standard shrader valve. Like a bicycle valve. You should be able to remove the gauge, then press the relief on the gauge to remove pressure.

ECU controls injectors, not fuel pressure.
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