Intermittant crankshaft sensor not allowing car to start?

[Pagan]

Hi all, My 2.0i E85 not been starting recently.  It cranks and almost starts but not quite.  I've checked all the basics (e.g. fuel, battery, spark), as well as various more complicated things.

So far, the only slightly off thing I've found is the crank sensor.  When I hook up a multimeter, the sensor signal is reading 0V until I put some metal on it and it rises 12V.  This seems the inverse of most sensors (which also seem to be usually 5V) but I assume it’s okay.  Probably more importantly, about 1 in 10 times I put metal up to it, it gets stuck on 12V even when the metal is removed.

However, I'm not getting regular error codes (2B63 exhaust cam shaft sensor a few times which I've checked and is okay, and 2B5C crankshaft sensor once).  Anyone have any thoughts on whether it’s worth buying another crankshaft sensor? It looks like it would have to be second hand, as they don’t seem to make them new.

Thanks.

[Pagan]

Any body have any experience with camshaft sensors?

It would be great to know:
a) whether it's normal for these to rise to 12V (rather than sink to 0V) when metal is present (not seen any reference to this anywhere online)
and
b) if it matters that much if it's occasionally getting stuck at a voltage (at 12V in my case)

[r3vmatch]

Hi Pagan,

My Z4 (N52 / 3.0si) also had a "long crank" issue ; it got to the point it would take a few turns of the key before the engine would start, sometimes 10-20 seconds of cranking. I replaced the starter motor which resolved the issue for me. I suspect there is some minimum RPM the ECU is looking for that the old starter just couldn't pull off. After replacement of the starter I haven't had a single long crank issue.

I had no codes being set. I also replaced the crankshaft position sensor at the same time (it was a "while I'm there") but I doubt it was the sensor.

I used a "new" Bosch starter when I did mine a little over a year ago but I think SEG is really now the "old Bosch" should you decide to buy a replacement starter. I think Denso also makes a compatible starter and had I known that, I would have instead used Denso.

See this for more details : https://www.e46fanatics.com/threads/bos ... e.1317766/

I'm not sure if debugging the sensor with a magnet or metal on the bench will tell you the full truth if the sensor includes any kind of "glitch filtering". It's possible the sensor output is "open-drain" or "open-collector" which means it pulls the output to 0V when there's a magnetic field and otherwise the ECU or external system has a "pull-up" resistor ; I'd be surprised if that's how it's wired but it's possible, usually the sensors include their own IC so I would expect the output to be what's called push-pull rather than "open-drain".

While not trivial to instrument, to really know if the sensor is working you'd want to use an oscilliscope of some kind to show you if the output is going high-low-high-low as the teeth of the gear rotate by the sensor.

These links are not from VDO (who made the sensors for our cars) but this should give you an idea how the sensor is supposed to behave with an actual gear:

• https://www.pico-automotive.co.za/new-d ... nnel-d.php

• http://www.techtalk.ie/wp-content/uploa ... mshaft.pdf

• https://www.tiepie-automotive.com/en/ar ... ensor-hall

The camshaft position sensors work the same way as the crank position sensor ("Hall effect" sensors), they will output a signal that alternates between high / low as the teeth of the gear on the camshaft go by the sensor.

[r3vmatch]

BTW:

For my N52 I was able to source a new VDO branded sensor (rather than BMW marked up parts) for my crankshaft sensor, I also replaced both camshaft sensors (VDO) when I was troubleshooting a rough idle. I don't know if you can find a VDO branded part for your car rather than "BMW OE".

A quick check of the sensor for your car (I think BMW P/N: 13627548994 , https://www.realoem.com/bmw/enUS/part?i ... 3627548994) shows FCP Euro has it: https://www.fcpeuro.com/products/bmw-cr ... 3627548994

[smorris_12]

I suspect there is some minimum RPM the ECU is looking for that the old starter just couldn't pull off. After replacement of the starter I haven't had a single long crank issue.

Yep. Generally modern ECUs want to see a minimum crank speed before they'll attempt to fire. For the 6 pots it's 150rpm.

[Pagan]

Thanks for the thoughts—very much appreciated. I decided to try a (second hand) crankshaft sensor, but it’s giving the same signal as the original sensor, and the car’s still not starting.

I’ve noticed something odd—sometimes (on the old and new sensors), the signal inverts. So at times, it sits at 0V and rises to 12V, and other times it sits at 12V and sinks to 0V. Surely that inconsistency can’t allow the engine to time itself?! I could try a brand new sensor (thanks r3v), but it seems a little strange that the two sensors I have are doing the same things.

INPA is showing RPM as over 200, so I assume that rules out a starter motor issue.

[Pagan]

If it’s useful, I’ve checked the following:
- it's sparking
- spraying fuel
- topped up oil (no way of testing level since no dipstick)
- added some fresh fuel
- battery voltage fine
- checked all fuses in glove compartment and box in engine bay
- engine sensor connectors reading as 12V for + and for signal connector, 0V for -
- checked chain is taut
- crankshaft turns fine manually (but quite stiff at moments, I assume due to compression)
- cylinder valves opening (not much on the intake, I assume due to VANOS)
- cleaned oil cyclone separator and hoses
- locking/unlocking from key button, so assume key battery fine

Again, symptoms are:
- cranks fine
- almost sound like engine starts (low rumble), especially if left standing for a while, but not fully
- there were 3 beeps when trying to start a few weeks ago but not now
- no error codes (was getting 2b63 and 2b5c but not now)

Between starting (6 weeks ago) and not starting (4 weeks ago), I had:
- changed the oil housing filter gaskets
- cleaned engine bay (had bag over engine)
- may have had key in ignition (but all off) when battery was disconnected

Anything else you’d recommend checking? Thanks again.