Quote:
Originally Posted by SnapCoupe
I have been trying to figure out my long crank issues ever since I purchased my car around a year ago. The symptoms are as follows: Whenever the car sits for more than 6 hours around 50% of the time upon the first press of the start button, the car will continue to crank but refuses to start. If I press the button again to stop it and once more to try to start it again, it will fire up immediately. When it is colder than about 50 degrees F outside, this will happen just about every time the car sits for longer than 6 hours.
Without blindly replacing components, I have been trying to diagnose the issue to get to the bottom of it. I have ran multiple fuel system pressure tests on BMW's diag equipment, but all of them come back normal. I have logged plenty of runs with multiple styles of driving on MHD and my rail pressure is exactly where it should be. Unfortunately my car (2011) does not have a low pressure fuel sensor, so there is no way to tell if the LPFP is feeding the HPFP as intended. My best guess as of right now is that the LPFP is slowly dying out and upon initial priming of the HPFP, the LPFP does not have enough pressure to push the fuel to the HPFP. Hence why the second attempt to start always works.
In regards to these cars, the HPFP is always the one to go first. It's the weak link and replacing it seems to fix most fueling problems that people tend to have. Though, I am curious to hear if anyone has replaced a LPFP on a 2011 without the LP sensor. If so, why did you replace it? How did you know that the LPFP was the culprit? And, had you already replaced your HPFP prior?
Thanks guys!
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Did you do the testing or an actual dealer do the testing?
The rail pressure can be observed on cold start. It should reach setpoint pressure very quickly if the pump is good. Of course, multiple cold start tests would be useful to eliminate a fluke.