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· Registered
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Discussion Starter · #1 ·
I have a bizarre problem with our M43 engine (non-US) after a top end rebuild.

The cam position sensor appeared to be faulty, (bad idle and generally a bit rough). Also the coolant temp sensor appeared to faulty (by stopping the cooling fan from ever running), with the sensor connected the fan never ran even under extreme conditions; however, with the sensor disconnected the fan would run at high speed about 30 seconds after engine start and if the sensor was reconnected the fan would stop.

I've now replaced both the cam position and coolant temp sensors but with strange results:

1. If I start the engine it starts easily and runs smoothly.
2. If I then simulate a coolant temp sensor fault, by unplugging the sensor, the fan does not run as expected after approx 30 instead the engine cuts out and stops.
3. I turn the ignition off as the engine has cut out.
4. With the coolant temp sensor still unplugged I try to restart the engine but it will not start.
5. I reconnect the coolant temp sensor and retry to start the engine, but again it will not.
6. Unplug the cam sensor and the engine will start and run but rough.
7. Replace the cam sensor, the engine will continue to run and after a short while will settle down and run smoothly although it does seem an almost unnoticeable misfire.
8. If I carry out a diagnostic test with the sensors connected I get the following faults showing up:

* Signal, camshaft sensor.
* Activation, electric fan. (Note by me: coolant temp sensor initiates fan through ECU and electronic fan module)
* Misfire relevant to exhaust gas cyl 2. (Note by me: this is the cylinder that had the original problem requiring removal of the head. Metal debris in the cylinder caused amoungst other damage, the spark plug gap to close completely and most likely shorted the centre electrode to the top of the piston through that debris. The spark plugs are all new but the short circuit may have damaged the ignition coil module?).

After disconnecting the diagnostic tool the engine will not start and run unless I unplug the camshaft sensor first. After that it will start and run OK. Bizarre or what!!!

Anyone got any ideas on this problem?

· Registered
11 Posts
Discussion Starter · #2 ·


Usually (say 9 out of 10 times) the engine will stop after approx 30 seconds following hot or cold start. It will then not restart until the the cam sensor has been disconnected. Once started the cam sensor can be reconnected but if this is done too soon after starting, say within 30 seconds, the engine will stop and the proceedure has to be repeated. I've also noticed that after about 30 seconds of starting, with the cam sensor disconnected, the engine falters momentarily, which is about when the fan should cut in if the coolant temp sensor is open circuit, disconnected or possibly when the fan self test cuts it in.

I have an idea the self test part of the coolant fan control, cuts the fan in for a short while after a normal hot or cold start; can anyone confirm this?

I've just tested the old and new coolant temp sensors and the results are pretty much the same 2.48K and 2.46K ohms respectively at an ambient 22 degs, 0.33K and 0.35K ohms at a temp just off boiling. So I probably needn't of changed the temp sensor. I've also changed the cam sensor again, which although not embossed with the BMW logo is, I'm assured, a genuine BMW part made by Febi with the genuine logos etc ground off. They certainly look identical even down to what is left of the logo area but I remain sceptical on this point.

Does anyone know how to test the camshaft sensor, it's a hall effect device?

Being an electrician, although not automotive specific, I've unplugged the camshaft sensor, coolant temp sensor, DME module and tested for open circuits between the sensors wiring. I've tested for short circuits between the individual wires of each sensor circuit, the two ciruits themselves, to ground and found nothing wrong. I've checked for loose, bent, misplaced pins and connectors, again finding nothing wrong.

I've reset the fault codes and carried the required drive cycle several times to no avail. I'm starting to think the DME module has got its knickers in a twist or has one or more flags stuck but I can't find out if it is possible to carry out a reset of the device, either with or without lossing the factory/dealer settings. Disconnecting the unit overnight doesn't help.

I'm thinking of wiring in a switch to interrupt the 12 volt supply to the cam sensor and see if this gives me a temporary solution.

Apart from my switch idea has anyone got any clean suggestions as to what I can try next or where the problem may lie?
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