Over choking

[jacko]

Morning all, My 325i seems to be developing a starting problem, it is putting trough so much fuel that it is really rough, with some smoke,(not blue) but if i sit there with the revs up its not to bad. It seems to work itself out after a while but i have noticed my mpg is struggling to get to 20 mpg with easy driving. Any ideas anyone, cheers guys.

[Andy_magic]

Hi,

How long does the rough running last on a cold start, if its a few seconds then your possibly looking at leaky injectors.

(Assuming its Motronic)

If it lasts for more than that you need to check the blue temp sensor and it's connection to the ECU. The specs are 2.9K ohms (ish) when cold and 300 ohms (ish) when warm.

If its the earlier type injection system there is a thermo time switch near the blue temp sensor that needs looking at, and I think a relay somewhere.

Both my E30's are motronic so I haven't looked into earlier systems

[Brianmoooore]

Figures I have, which are actual measured values are:

brown sensor:
828 ohms at 16 degrees
185 ohms in hot water (probably from tap)
63 ohms at normal engine temp.

blue sensor:
2930 ohms at 16 degrees
860 ohms in hot water

another blue sensor:

3400 ohms cold
980 ohms hot water
306 ohms, very hot water

Another FAULTY blue sensor:

7200 ohms cold
1960 ohms hot water
722 ohms, very hot water
The temps for this sensor are the same as the one above. i.e. a direct comparison of a faulty sensor with a good one.
The symptoms of the car which this sensor came from, (which I bought v. cheap because of them), were rough idling when hot, and hesitation when accelerating..

[Andy_magic]

The symptoms of the car which this sensor came from, (which I bought v. cheap because of them), were rough idling when hot, and hesitation when accelerating..

Ditto - lol

[jacko]

Yep, i fully understood all those values So would it be easiest to just replace the blue and the brown sensors? Andy_magic, yes the symptoms do last for more than a few secs, it seems to be a good few minutes. Cheers.

[Brianmoooore]

Just the blue one. The brown one just works the temp gauge.

[Andy_magic]

If you start the car from cold and drive about a mile then switch off to say go into a shop, is the car sometimes really hard to start, but will fire up ok if left for a while? I had these symptoms on one of mine and it was sorted with a blue temp sensor change.

[jacko]

Now you come to mention it i think those syptoms are developing as well, sounds like a new sensor this coming w/end, Thanks.