A little while back I posted this problem-
'86 745T went from running well to iffy idle, slight misfire, poor mpg, lower performance.

This happened while on the highway, heavy right foot, nothing I hadn't done before.

After some basic troubleshooting, I found the ignition advanced to about 35 degrees BTDC. I rotated the distributor as far as possible to the driver's side, and could only bring it back to about 25 degrees BTDC. Idle improved somewhat, performance and mpg still lacking.

On other's advice, I've checked the following:

Coolant Temperature Sensor- I've checked the wiring, resistance values, and voltage at the ECU, all both hot and cold. Everything checked out within spec.

I read up on this and the temperature switch that controls the a/c cooling fan that when closed sends 12 volts to an input on the Ignition ECU. This switch is mounted on the radiator. The Haynes shows that this voltage powers the fan and tells the ECU to advance the ignition 15 degrees or so at idle (throttle switch closed).

I disconnected this harness to ensure that the input wasn't being triggered. I measured voltage at the firewall from the A/C controls in the dash. It was hot, even with the a/c turned off. I tested the fan- it works properly. I figure this fan/switch and ecu input work properly, and will double check after replacing the fuel pressure regulator this afternoon. I will also check the a/c relay operation.

I've also checked the integrity of the crank pulley and the timing belt. When the crank timing mark is lined up on zero, the lobes point straight up on cylinder #1, and after removing the spark plug I can see that the piston is at TDC. I'm reading from this that the mechanical timing is where is should be, and the crank pulley does not exhibit any "spinning" effects when under the timing light.

I know of no other way to adjust or affect the timing than these devices. I was told by the past owner that they had the timing "advanced" as they were running 15 lbs or so of boost. I removed the Dawes device involved after the onset of symptoms (kicking myself for not doing it earlier).

Any input on this diagnosis, or more clues, would be great.

-Dylan