Intermittent rough running SC (long)
 

My '82 SC is running rough. I am thinking it is an ignition problem. Some times it starts up and runs OK, though never smoothly. Yesterday, it started and ran really rough, popping quite a bit out of the exhaust. I drove for a bit to see if it would settle out when warm but it didn't. After pulling over and shutting down, it started up and ran like normal. This also seems to happen every time I give it a good workout, up to red-line. Every time after a quick 'Italian tune-up' it starts the popping and goes back to 'normal' when I stop and restart the engine.

Just completed a top-end rebuild where I replaced cap/rotor, all plug wires, new plugs, every hose in the CIS, cleaned and tested injectors (replaced one leaker), SSI backdate and M&K muffler, chain tensioners and new ramps, all CIS air leaks taken care of including new airbox.

I have the timing set correctly, the CIS pressures are right in spec and I have used a LM-1 to set the A/F mix.

Plugging/Unplugging the O2 sensor (new) doesn't seem to make any difference.

The only think I can think of that would reset itself after shutting off would be the Perma-Tune box (old blue one). My thought is to replace the permatune and coil as I can't come up with anything else. It starts OK, sometimes takes a little cranking but it has always started.

Sorry for being long winded but I am a little frustrated. Looking forward to a smooth running engine.

What else should I check? Is there a way to bench test the Perma-tune and/or coil?

Any thoughts greatly appreciated.

Given that you've covered all the bases for the problem during the rebuild, you're probably on the right track to check the Permatune/coil. Backfire through the exhaust could be related to poor ignition so that's consistent. See if you can borrow a known good CDI and coil to test--it's simple and cheap.

Thanks for your input L.J. Nice to know my thoughts are at least reasonable. I will check to see if I can find known good units to test.

Anybody in Minneapolis have a spare CDI laying around?

Bump for other thoughts? Am I on the right track?