All right guys I'm new here and I think you guys seem to know a lot and I need some advice. Just recently I noticed that my engine will not get over 3500 rpm and the tach started bouncing around, but when the Tach isn't bouncing the engine runs just fine. Today I went through and checked the distributor, ignition control module, and checked the coil. They all seem fine. I have an Accel Super Coil and the distributor cap and the ICM are cheap aftermarket or Factory respectively. (I think) I really wish I knew what the heck was goin on. Any help from you guys would be great. I took the ICM to Autozone they checked and it said it was okay.

 

Your bouncing tach and related poor performance are indicative of a true ignition problem, likely on the primary side since the tach is involved. Items to concentrate on would be the coil primary windings, HEI module, all wiring connections, the capacitor in the base of the distributor, the pickup coil and reluctor, and power supply to the ignition system.

Since the coil is not stock, you may want to switch back to the original coil for diagnosis before you do anything else. Don't be too surprised if that solves most of your problems. Aftermarket coils generally have a higher primary current than the stock HEI module is designed to switch. The problem gets worse at faster switching rates (higher RPMs). The switching transistor saturates at higher RPM and cannot switch off the coil primary winding with the lower resistance aftermarket coils. The result is erratic spark, misfire, and the bouncing tach signal.

There are aftermarket HEI modules designed to work with aftermarket high current coils. You may need to get one is you decide to keep the aftermarket coil. The HEI module probably tested just fine, since it is within specs for a factory coil load.

Incidentally, welcome to the boards! You're right. Many of these members seem to have a good handle on what's happening in the garage.