All right guys I gots a problem. A week ago my engine (5.7 TPI '87 GTA) would not get over 3000 rpm when the tach was bouncing or not even close to accurate. It used to be right on the money or close anyway. I replaced the Ignition Coil Module with a Accel one. It fixed the problem where it wouldn't get over 3000 rpm but now the tach is screwed up. It just bounces a lot but when it gets ready to shift the tach drops down to 3000 rpm to shift then once it shifts it shoots back up to 4000 - 5000 rpm range and just bounces until I let off the throttle. Could the wiring for the tach be messed up? I'm not sure where to start looking for problems. Help would be the greatest.

 

I would suspect you are dropping one or more spark plugs intermittently, which the tach would read as a lower rpm (sparks / minute). Check to see that your spark plugs are in decent shape and they are all firing. This happens to me now and then when my plugs foul up.

 

Does the car have to be warm before the tack starts to mess up? Can you feel the car jerking with the tack movements?

I had a problem very similar to this. After I had driven the car for 15 min the tack would start bouncing around and would only get worse the longer I drove it. It turned out to be a lose ground wire on the back of my passenger cylinder head.

 

The car doesn't jerk when the tach bounces it runs just fine. Thanx for the help.

 

EASY fix, it's the pick up coil inside the distruator, it's right on the saft and is what picks up when to fire each plug. They start to go to ground causing a jumpy tack, it's a good warning sign becasue sooner or later it will fail and the car won't run at all. Just put in a new one and your problem.