2001 e46 318i Touring - Bizarre ECU/engine problem

[duffsparky]

I have a bizarre problem with our 318i Touring 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?

[dave45056]

I'm not familiar with this engine at all. But could it be that the two sensors are plugged in to the harness incorrectly? You have to disconnect many things to do a top end rebuild. So look to see if it is possible to get these two reversed.

[duffsparky]

Hi Dave,

It's nigh on impossible to get the connections wrong as the connectors are unique to each device, nevertheless thanks for the suggestion.

Regards.

[Junk]

try swapping coils and see if you get the misfire on another? Sounds like it was sort of running OK with the new cam sensor? for awhile at least?

[duffsparky]

Originally Posted by Junk

try swapping coils and see if you get the misfire on another? Sounds like it was sort of running OK with the new cam sensor? for awhile at least?

Hi Junk,

The problem doesn't cause a misfire, the engine stops altogether after about 30 seconds.

Thanks anyway.

[Junk]

"and run smoothly although it does seem an almost unnoticeable misfire."

"* Misfire relevant to exhaust gas cyl 2."

I just meant to see if the diagnostic shows up on a different cylinder, as you mentioned if the coil was somehow damaged, then you know the coil is bad and perhaps it is somehow causing the ECM.. err DME to freak out?

("somehow" and "freak out" are technical terms for "I have no f-in clue buddy!")

two bad camshaft sensors? If they are old, mine had cracked insulation and wires would short intermittently...

[AquaCali]

As far as the camshaft sensor goes I would double check that the connector is on the right plug. On the M44 the connector under the intake manifold is for the camshaft and crankshaft sensors, the connector is not marked for which one goes were. On the M44 the camshaft sensor is connected to the connection to the front and the crankshaft to the rear connection. I do not know how much BMW changed for the E46 series 4 bangers.

[duffsparky]

It's not possible to get the connections wrong on the M43, but thanks anyway.

[duffsparky]

UPDATE:

The possible misfire seems to have gone. The compression, when cold, on number 2 cylinder was about 116 PSI whereas the other 3 were all around 198 PSI.

The engine also had a tapping noise when cold and under gentle load, that would slowly go away(?). After seeking advice there seem to be 3 possibilities:
a) sticky hydraulic lifter.
b) pinched or sticking piston ring cause by original engine failure.
c) small end, unlikely as noise would all but disappear as the engine warmed up.

I put some hydraulic additive in the oil to see if it would help. Not sure if the additive or time did the trick, but the tapping noise went and the number 2 compression came up to that of the others.

Still got the engine cutting out after 30 seconds problem though.