| When you change chips you often have to make a minor adjustment to the CO trimmer to get it to idle properly.
1.6M ECUs (748/916 Biposto/ST2)
On these ECUs the trimmer is located inside the ECU and the rubber bung must be removed for access.
Next to the chip socket there's a very small (1/4" square) trimmer potentiometer. This has the same function as the external trimmer screw on P7 and P8 ECUs. The trimmer on the 1.6M ECU has a range of about 3/4 turn, or 270 degrees. When you hit the end stop, STOP ! There is no roll-over on these trimmers and they will break if you try to force them.
When you screw the adjuster clockwise the mixture is leaned. To set the default position, simply set the trimmer in it's mid-rotation point. You can also use a voltmeter to set the 2.5 volt point.
Setup
1/ turn it clockwise until it stumbles. remember the position - lean end.
2/ turn it anti-clockwise until it stumbles again. remember the position - rich end.
3/ turn the trimmer back clockwise until about 1/3 of the distance between the two stumble points from the lean end.
This usually ends up at about 4% CO all the times i've done it and checked it. If you don't get a stumble point, there's not much you can do. Wind the airbleeds in if there's no rich stumble point, out if there's no lean stumble point.  |