D4 3.0 TDV6 crankshaft position sensor failure

[DiscoJeffster]

This might be helpful for someone chasing down weird behaviours.
Symptoms started out as

- occasionally the engine cutting out immediately after starting.

- a slight hesitation felt occasionally when cruising (felt like brief timing retard on a petrol engine)

- developed into refusing to start whereby the engine would start and run then splitter to a stop. Repeated attempts to start resulted in less running to the point it would continuously crank and not run.

Finally when driving one day it gave up and flagged an error P0036-31 crankshaft position sensor. I got it going again after a few minutes and got home for it to never start again.

While I could see fuel pressure sometimes when cranking, when the signal is poor/fluctuating the ECU stops fuel pressure (assumes the engine isn’t running) and that was why it would run and splitter to a stop and then not start as all the fuel pressure was depleted and no signal to tell it to pressurise the HPFP.

Repair wasn’t easy - suspension components need to be moved, drive shaft removed from diff (resulting in an aged CV boot failing and needing replacement) to get into it. 3.5hrs labour all up. The fault also got the ECU into a tizz and even when the sensor was replaced it wouldn’t start. It took an ECU reflash to get it running again, weird as that seems. Work was done by a reputable Indy.

End result is the car starts like it used to, quickly, and without any hesitation. I think the sensor had been a bit dicky for six months looking back on it.

[Graeme]

Live value monitoring of the sensor when an engine falters but no fault codes are stored can reveal the sensor stopping coincidental with revs dropping.

[DiscoJeffster]

Live value monitoring of the sensor when an engine falters but no fault codes are stored can reveal the sensor stopping coincidental with revs dropping.

Agree. But with so many sensors and no indication what was the issue, it was needle in the haystack. In retrospect, I’d now have done cam, crank, etc.

[Graeme]

My association with unexplained stopping caused by a faulty crankshaft position sensor goes back a long way to a friend's new V6 Commodore which would run when cold but intermittently stop thereafter, for which the dealer swapped parts until the fault no longer occurred. At least for those engines a spray of cold liquid on the sensor which was located behind the front pulley would cool the sensor to cause the engine to run again. With the availability of reasonably cheap diagnostic tools reporting live values these days the guesswork can be avoided.