title says it all. but if i disconnect it, it runs fine(low idle but still fine). ive replaced the ignition control module, blocked off egr, no cats. no SES light on.

what all controls the timing advance on these beasts

 

The pick up coil in the distributor generates a pulse and sends it to the PCM. The PCM calculates what ignition timing should be, and sends a modified pulse back to the ignition module through the tan/black trace wire. The ignition module sends the pulse to the ignition coil, and it fires. When tan/black trace wire is disconnected, the ignition module applies base ignition timing directly to the ignition coil. This is when base ignition timing is checked with a timing light. When the tan/black wire is reconnected, it overrides the base timing signal to the ignition coil.

 

ok so i replaced the pick up coil and after a yr of fighting with this its fixed!!!! idle is fine tan/black cord is plugged in, it looked fine, but for 12 bucks i was willing to change it as i had already done every other sensor

 

The pick up coil moves back and forth each time vacuum on the vacuum advance unit changes. The constant flexing of the tiny copper strands of wire inside the insulation, causes them to break. Unless the insulation breaks, you can't see the problem. As the wires flex, they can lose contact completely, and the engine stumbles, vacuum drops, and the wire makes contact again. When the last strand completely breaks, the engine will not run. If you tug gently on the two wires, they might just pull apart and you'll see the broken strands. Pretty common problem with HEI distributors.