I'm working on a 1994 Formula with a 396. The engine has been running poorly ever since the dynaspark to a dump a few months ago. We've installed a new dynaspark and the engine still will not run properly. Prior to the dynaspark crapping out, the car made about 440 RWHP. Now, with the new dynaspark, it will only make about 410 RWHP.

When datalogging the car with Diacom, the only thing that looks way out of whack is the IAC count, which is pegged at 160. The engine is supposed to idle at 900 RPMs, and will now only idle at about 650.

Today the battery died in the car. We hooked up the battery charger and started the car. It immediately fired and idled at 900 RPMs like it's supposed too, and the IAC counts came back in line. We removed the battery charger and the car immediately went back to running like crap.

We then unplugged the alternator and the car began to run great again. We made a quick pull on the dyno, and set a new best of 448 RWHP with the car. Hooked up the alternator, right back to 410 RWHP and the car running poorly.

We replaced the alternator with a known good unit with no change in the symptoms. We now suspect PCM, but I would like to gather some opinions before swapping out ECMs.

Thoughts?

 

Put a voltmeter set to AC on the output post of the alternator and the negative battery post. If the meter reads over 0.03 VAC the diodes are defective. Too much AC leaking out of the alternator can create all sorts of problems.

 

It's got a known good alternator on it right now, but we checked it as you describe and it seems to be OK.

Swapped EMC's today with no change in symptoms.

Any help is appreciated.

 

I dont know about your altenator, but my ECM has nothing to do with the charging. There are two wires. One large that carries all of the current and one small feedback wire that goes to the positive terminal block on the fender. Which are you unhooking?

 

Unhooking either one will make the car run properly.

 

Sounds like a bad altenator to me.

 

But he said a good known one works... check the wires themselves. replace if necessary.

 

Check the wiring for breaks, frayed wiring, grounding, and corrosion. Have you checked the output of the altenator?