E39 530d intermittent starting issue / cutting out
Discussion
Got a 2001 E39 530d here. Had it about a week, in that time every now and then it'll cut out. Sometimes it'll start straight back up, other times it'll need to sit 20-30minutes else it just cranks endlessly. Sometimes before it cuts out it'll start running rough and struggling to idle. Symptom wise it looks like a fuelling issue, however when plugged in it ran no codes at all; normally failing fuel pumps would throw a code for low fuel rail pressure. Could it be injectors? I'm baffled by the fact that it hasnt thrown a code...
Its had a new fuel filter and pumps seem fine; ran proper diagnostics today, pre supply and rail pressure are about where they should be. Did a leakoff test expecting a few dead injectors but instead they were fine; what we did notice however is the rubber glove used to seal off the return to tank line (which should just operate on a basic vacuum from the tank) started inflating from backpressure! Under the glove was a cap on the t-piece so the pressure was sufficient to blow the cap off and start inflating the glove. No idea what could cause backpressure from tank through return line?? The return line seems to take quite a complex route through to the tank, taking two routes and interchanging with the feed lines presumably through two one-way valves so perhaps they are dead. During the leakoff test with the injectors just leaking off into unsealed bottles, it ran fine; upon reconnecting it ran like a dog again. Then when putting the return line into a bottle, it still ran like crap so it was perhaps a coincidence that it ran better but the return line backpressure is still not a good sign. It also has a mystery vacuum hose disconnected which appears to come from the vacuum chamber under the turbo. It leads to the inlet but is just hanging off not connected to anything so need to figure out where that goes. All in all, good that pump and injectors or fine but I am truly lost now and searching for this issue just brings up stories of people replacing pre-supply pumps or injectors and the issue going away. Very much lost now. Does anyone have a fuel / vacuum diagram for the M57B30 engine?
It does but the issue comes regardless of fuel level unfortunately. At the end of my tether with it, I'm pretty mechanically competent and have dealt with fuelling issues before on cars, beyond that I've had 4 different people look at it and try and diagnose and none of them have any idea. I've read pretty much every single thread on M57 issues / misfires and nothing seems to have narrowed down the extremely strange symptoms. Beyond that, the ECU will now no longer talk to any code readers. Tried two different ones on two different occasions and they wont communicate at all. Starting to think it could be a fried ECU but being an EWS 3 car with the diamond shaped key a new ECU is not a cheap nor easy solution...
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