I am trying to determine what is going bad on my ignition system. The truck misfires/backfires while accelerating at higher RPM. It idles smooth. I have a new ballast resistor, coil, different distributer, and new cap and rotor button. Any ideas? I have changed ECUs but was a used and definatley bad unit. I also have squeezed the connectors to make sure it had a good conection.

John

Well, I had a bad ecu a little while back and I noticed that it made for really hard starting. Once I got going, it seemed to run just fine. That doesn't mean you can get different symptoms with yours.

You replace with a new ECU, they don't last forever and last I checked they are only about $25.

My other thoughts are a bad coil (yes, you may have a new coil, but that doesn't mean it isn't bad already) If I understand correctly, cutting out at higher rpm is a sign of a weak coil.

A bad vacuum leak (maybe loose carb mounting bolts) or a stuck open EGR could cause problems at higher rpm under load, so take a moment to check.

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1980 Aspen 225 super six

If you think it might be the ECU causing you problems, many parts stores have machines that can test them off the car. Just make sure you have it tested 2 or 3 times consecutively so that it build up enough heat to expose any faults.

When was the last time you changed your fuel filter? Have you tested your fuel pump and inspected for leaks/cracks in the fuel lines. Your problem could be ignition related but the same symptoms could be caused by fuel starvation.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

The fuel filter has been replaced. The fuel pump was replace not that long ago, but while changing the filter recently, the pump had a lot of pressure on it. The reasons for the ecu question is this truck has notoriously been hard to start by key. Often a 2 foot roll off would have it running after grinding and grinding on the starter. I'll check for vacuum leaks.

I guess the fuel pickup tube could be clogging also giving starvation symptoms.

I'll try another "good" coil (tested in another vehicle)