Model 245GL wagon

Engine: B23F or B230F (according to tag) with an "847" on the timing belt cover.

The engine pings under fairly light acceleration, making it a real pain to drive the car. We have tried different gas, short of the most premium grade. Another 1984 with the same engine we had before had no problems with regular gas with an octane rating of 86.

At first I thought that a mechanical advance system might be to blame until I found out there is no mechanical advance on these particular distributors. If I set the timing at 12 deg BTDC at idle, the engine advances to over what I would guess at 40+ degrees on the crankshaft at highway rpm.

I have checked the wiring back to the ignition control module and the wiring looks good here.

I looked at the vacuum module on the ignition control module and determined it has variable resistance according to the following short table

no vacuum 68 ohms

5" vacuum 93 ohms

10" vacuum 123 ohms (this is the idling value at roughly 7000’ of altitude where we live)

I am wondering what might be next. I have also replaced the knock sensor which now retards when the engine block is tapped above the oil filter boss area while idling. I thought this might fix the problem; it did not.

I have tried power timing the engine but it needs to be adjusted so far that I cannot start the car or keep it runnig when started from a cold engine.

I have looked at my partial set of Volvo manuals and a Haynes manual and I cannot find any other suggestions at this time.

Has anyone else have this problem before and discovered a solution?