Sporadic Ignition Timing when the Engine's at Temp

[GRONK]

Could be.  Curious though, how does the EGR dictate backpressure.  I understand the CTO and the ported vacuum.

[ammachine390]

Could be.  Curious though, how does the EGR dictate backpressure.  I understand the CTO and the ported vacuum.

Basically, the pintle is hollow and has a hole at the end of it, the exhaust pressure can travel up the hole, when the pressure is great enough, it overcomes a spring, and seals the vacuum chamber, so that vacuum can move the pintle and allow egr flow. Pretty interesting how it works.

It's explained here in the 1982 Jeep TSM, on page 74. I think the same exact thing is written in my 81 TSM, but I don't have it for reference. This is a big file and takes a while to open.
http://oljeep.com/gw/82_tsm/Part%201%20Section%20J.pdf

Here's another site that explains it and can open a lot faster.
http://www.tomco-inc.com/Tech_Tips/ttt26.pdf

[GRONK]

Interesting.  Never knew.

[FreedomMachine]

I added another ground to the ICM and there was no difference.  I replaced the ICM and there was no difference.  I check the ignition and pick-up coil both were nominal . The timing is bouncing around after the car warms-up. I can see the vacuum advance isn't doing anything strange. Could the SSI in the distributor be over heating? would that cause misfiring?

Has anyone else had this problem before?  

[ammachine390]

Maybe try taking the distributor cap off and make sure that the trigger wheel and pickup is still clean/ok. Also, there is 3 wire harness that goes into the base of the distributor, the black wire is a ground for the ignition system, which is connected inside the distributor to the engine for a ground. Its been known to corrode causing misfires, make sure its clean.