I have an 350 cid TPI engine and 700 R4 trans from a '92 Z28 Camaro in my '55 Chevy. I am having an intermittent problem and I am hoping someone else has experienced this same problem.

All the wiring in this old car has recently been replaced, although the problem in question started before I rewired the car. The TPI ECM harness was not replaced,, or redone. The ignition module, cap, rotor, and coil are all new.

Whenever it feels like it, the engine starts running like the ignition wires just got crossed, with an occasional backfire through the exhaust. At the same time, the tach wigs out and ends up pegged out at 7 grand. This usually happens at slow speeds, under 45 or 50 mph. About three times back, it happened while sitting in my garage, at an idle. When this happens, I just turn the key off, restart it, and everything is fine, until it feels like screwing up again. With the engine idling, I've tried wiggling wires coming out of the ecm, and under the hood, and can't make the problem happen. It just does it randomly.

Any of you ever had or heard of this? Does it sound like maybe I should go through the expense of replaciing the ecm next?

Thanks for any help!

Chris

 

I doubt your ECM is causing this.
If you're going to wiggle or inspect anything it should be your secondary side of your ignition system.
I would check your plugs and plug wires very carefully.
Make sure your plug-wire's impedance measures good and that they are not running together parallel or touching metal objects.

Plugs can also be tested with an ohm-meter. Check for cracks in the insulators. make sure you're not running plugs with the screw-on tips. Resistor plugs can crack internally which can cause intermittent misfires.
Make sure your ignition system is well grounded.

There is some spark plug info at the link in my signature.

 

Ok, the plug wires and spark plugs are the only thing left that I have not changed. If I understand correctly, you're telling me that one or the other, or both could cause the tach to act weird and peg at the 7 grand mark, until I shut the ignition off and restart it? The minute it restarts, it runs great again. That is of course, until the next hiccup~~~
I can surely put new plugs and wires on it! Thanks!

 

The grounding of the ignition module and coil is also a possible cause.
I would test the wires & plugs before assuming they are bad and swapping them. You may find a bad ground on your coil before you get that far.
Also check for play in your distributor shaft while you are at it.
Look for evidence of arching from the coil, cap, or wires.
Test any wiring you have between your module and coil.

Most times i've seen a tach act up like that is from a loose ground connection, but you also have the engine misfiring as well, so it's hard to say for sure you don't have more wrong than that.

edit: I have also seen a bad alternator cause the tach to go nuts, but no misfires with that.