Hello,
I've got an 88 IROC 350 tpi. For the past couple of months I've noticed that my tach would bounce and the car would stutter for a second or so. This would only happen maybe once every other week. I just replaced my coil, rotor, cap, wires, and plugs. The problem did not go away and has gotten worse. It does it probably once every ten miles now. It happens when the torque converter is locked up so there is more load on the engine. It doesn't seem to do it at wide open throttle. I'm guessing this is because I put in a MSD coil which has higher voltage and its aggravating the problem more than before. My distributor failed a couple of years ago and I had a rebuilt one put in. I'm wondering if the problem is the pick-up coil in the distributor. Does anyone have any ideas on this one? Any help is appreciated.
thanks
Craig

 

CSwanson,

Welcome Aboard!

No one can tell you positively that the problem is the pickup coil or reluctor, but it's a fairly reasonable possibile cause, and it's easy to test them. You can measure the resistance of the pickup coil to determine it's condition. The acceptable resistance range is 500-1,500 ohms. 850 is about dead-on for a new coil. You should also test the resistance from the coil leads to a good ground. There should be no reading on the highest resistance scale (megohms). Any variation from those parameters can mean the pickup coil is on it's way to the copper recycler. While you're in there with the meter, test the filter capacitor in the base of the distributor as well.

You should also visually inspect the pickup coil for discoloration, cracks in the insulation, and look at the reluctor (moving pole piece) for excessive rust of minute cracks. Heavy rust on teh reluctor or pickup poles on the coil piece can cause a poor cutoff of the impulse to the HEI switching module, and erratic spark. Obviously, any degradation of the coil itself or its insulation can cause a similar problem.

Checking is easy. If you have to change it, that's a different story. Not really difficult, but it can be time consuming.

Start with those components, since ignition is a likely cause. It is also possible that you have a fuel deilvery issue, with injector pulses or the injectors themselves, but the ignition is the prime candidate.

 

Thanks for your response Vader. I have a question... you said it was easy to measure the resistance of the coil. Do I have to remove the distributor in order to take this measurement or do I just remove the cap? Thanks for your time.
Craig

 

The pickup coil can be tested with the distributor installed. Remove the cap and rotor, then unplug the pickup coil connector from the amplifier/switching module.

 

Well, I checked out the distributor and the pickup coil measured 850 ohms with no fluctuation when bending the wires. The ground reading was correct as well. There was no sign of any rust. The problem is getting so bad that I can't drive the car. Any ideas on what else this could be? I have to believe its ignition related, not fuel... The tach bounces (engine stays constant but stutters) about +/- 750 rpm now without even being on the gas. Should I just take a chance and replace the distibutor? My dealer wants $275 for a new factory unit (AC Delco) which I thought was pretty expensive.
thanks

 

I just wanted to add that I scanned my car with my auto-xray scanner and everything looked normal so ECM failure can be ruled out.
thanks

 

Well, I replaced my ignition module (with a Standard brand part) and the problem went away completely for about 6 weeks until yesterday. So when I got home I put in a new AC delco module. I thought it was fixed but it happened again today. I measured my pickup coil and it was 850 ohms exactly. What else could it be? It is exactly the same problem that occured when the ignition module went bad?
thanks for all opinions.

 

It could still be the pickup. My car burned a module every two weeks (miss/no restart) until I just changed the pickup and the problem went away. It had an intermittent problem I suppose.

 

Thanks for your reply. Maybe it is the pickup coil. Maybe I should try measuring it when the car is really hot. I think its definitely heat related. I've only measured it when the car was cool because I didn't want to get burned.

 

Oh, and one more thing... you said you burned up the modules... Do you mean that you wrecked them by having a bad pickup coil? Can a bad pickup coil actually damage the ignition module?
thanks