Crank Sensor

[Coslin]

Can a crank sensor failure on the m62tu cause an extended crank *without* a check engine light?

Car drove fine for 2 days and all of a sudden I have a crank no start. With both keys. Recently the car had the immobilizer replaced so I wanted to try to rule out a key.

Thanks for the suggestions!

[Timm]

Yes, a failed CRANKshaft sensor rarely gives an error as it is used as a timing signal for the DME. But, extended cranking is often caused by a fault CAMshaft sensor - you can disconnect it and the car will run fine (but with less power and higher fuel consumption) - if the cranking time reduces immediately that will be your problem.

http://www.meeknet.co.uk/E31/BMW_E31...eplacement.htm

[JTL]

My e38 started cranking longer but does end up starting on the first try. Car runs 100% after start and no codes are present. This only happens if the car sits for a while. If I turn the car off and restart within a few minutes it starts normally. The crank sensor checks out with multi-meter but has never been replaced. The cam sensor was replaced last summer. I don't like to just throw parts at the problem but have a new crank sensor on order. I have doubts that swapping the cs will fix the issue as this seems more like a fuel delivery problem but we'll see...

jt
-98 740iL

[Timm]

Yes, that is classic symptoms of losing fuel pressure when the engine is not running. Fuel pressure should be retained between the fuel pressure regulator and the fuel pump indefinitely (in practice it drops to 2.5 Bar after the engine stops and then maintains that pressure for weeks).

Obviously the first thing to do is measure the fuel pressure somewhere between the pump and the FPR when the engine is not running - but the two suspects are the fuel pump itself (which has a non-return valve built into it), and the FPR (which can leak, often via the vacuum pipe that runs to the PCV) - a test for that is to pull the vacuum pipe and see if it is wet with fuel:

[JTL]

Replacing the crack sensor didn't improve/fix the prolonged cranking at all. Next check fpr and fuel pump. Those should have been the first items to check.