Found a well hidden botch/mod by a PO on my car yesterday afternoon. I had to temporarily unplug the 3 plugs that connect to the engine in the back left of the bay. Whilst disconnecting the plug for the cyclinder head temp sensor (the white plug) I felt something give, as if a wire inside had pulled loose.

I pulled back the rubber grommet to find that a 220ohm resistor had been soldered in series with the signal wire, and it was a solder joint on this that had broken one end. Although it was obviously not, I checked the wiring diagram to see if this should be there - and it shouldn't.

The only thing I can conclude is that it's some attempt to fool the ECU that the engine is running cooler that it actually is in an effort to run fractionally richer fueling?

Anyway, I repaired the connector without the resistor and all is good. Has anybody heard of this rather poor 'mod' before?

 

Sounds very odd! Can't see it changing the fueling as that is done by the temp sensor in the AFM.

 

The temp sensor in the AFM is for air temperature not engine temperature is it not?

 

Yes, and the air temperature in the AFM should provide the DME with information about the air temperature and I believe adjusts fueling.

Does seem like an unusual way to adjust fueling. It seems that adjusting the screw on the AFM would have been easier (even though that can get tricky).

 

Correct Rob, this determines the fueling at normal operating temps via calcs in the DME. The head temp sensor is only used for cold start enrichment as I understand it.