When I replaced the distributer cap recently, I noticed that on the inside of the cap....there are round arc nubs that accept the spark disribution from the rotor. It appears that the nubs are not tarnished in the area of the nub that is closest to the rotor tip. Rather, it is tarnished on the trailing area of the nub.

On older GM vehicles, you can usually get an idea of where the timing is by looking at the nubs inside the distributer cap (the nubs are usually flat and wider on older vehicles). Tarnish in the center of the nub indicates proper timing. Tarnish on the edges, usually indicates timing that is slightly off.


It appears that the distributer does not rotate on these. Is this correct? If so, is there a crankshaft positioning sensor that adjusts the spark? If so, where is it located?

Thanks,
Mike

 

The PCM controls the spark advance. Having never had my distributor out, I do not know if you can change the base timing or not, but if you do change it, the PCM may not like the change.

The CKP sensor is located on the timing chain cover behind the balancer and should be slightly angled towards the passenger side of the engine. Installing a new CKP sensor requires a crankshaft position variation learn proceedure to be performed (via a scantool with the proper capabilities). If it is not performed, then your engine may not know precisely where the crank is (and it does need a precise measurement for spark advance).