Daily driver ‘86 coupe cruisin along on a trip to the stores when she stopped running. Power still on, engine just died. No spark.

Process of elimination and testing and I replaced the module in the amp. Started right up! Great throttle response and better revs than before the failure. Excellent! But this is a jag and it wouldn’t be much fun if that was that.

Ten minutes into a test drive she missed a beat. I noticed she felt a little weak. I got another mile before I turned around and limped home at 1000rpm. She just didn’t want to run. Made it though. I’m now assuming that the actual fault that caused the first failure fried the first module and I’m on my way to toasting the new one. So what would cause this behavior? I haven’t been able to get back into it to check anything deeper after the test drive.

 

FWIW, I have never had a success with aftermarket, even genuine AC Delco, replacement ignition amps. In the end I bought a new genuine amp and no further problems. Having said that, check the loom from the bottom of the dizzy to the amp, remove the condenser inside the amp, ensure you use the heat-dissipating gel stuff under the amp, and make 100% sure the earth of the amp through the fixing bolt is good.
If you have the original coils replace them, a coil going home will fry the amp too, ditto if the HT leads are old, renew them, ditto check all the plugs and gaps - a duff plug fries the amp too.
After that no more ideas!

 

Thanks, Hmmm... I’ve been on the aftermarket module that just died for at least a year and a half, maybe more. That doesn’t mean that I didn’t just buy a duff one, but it worked great to begin with.

I checked the loom from the dizzy, although my pickup does not have exposed solder joints, the wires are molded right into the pickup. So I couldn’t check from there all the way to the amp. Condenser in amp is long gone. I applied a nice layer of thermal paste, and fitted it nice and snug.

Ground cable to the amp looks good, but I should pull a direct line to the battery negative just to test. I also converted to the single Coil. I checked the coil connections but didn’t meter the coil. I suppose that’s my next stop.

 

Delayed Update: Bad coil. Overheated the original module. Started to melt the second. Idling for five minutes, the new module was scalding. I replaced the coil and the module ran its normal temp, hot but touchable.

But I wanted to replace that second module with a third. Because the second module seemed to have built-in timing advance?! Had great power, but I couldn’t open it up much at all without detonation. Swapped to a Duralast DR100 ( Autozone part #17D20 ) and it behaved normally. No other change, tests ten minutes apart. I didn’t swap back to module 2 to confirm that it was the module, but I have to assume so.

Ive been running this new module daily for a few weeks without issues.

stay safe out there.

 

Question - my car is 89 -V12 and still has the original twin coils.
Is it worth swapping / upgrading to single coil?
Everything is going fine.

 

No. leave well alone. Assuming Lucas ignition? My own view is that the twin coil setup, with one of them in the cool airstream, is better.

 

But I wanted to replace that second module with a third. Because the second module seemed to have built-in timing advance?! Had great power, but I couldn’t open it up much at all without detonation. Swapped to a Duralast DR100 ( Autozone part #17D20 ) and it behaved normally. No other change, tests ten minutes apart.

Yes, some of the GM modules have built in advance. You want one that does not have any advance.

 

89 should be Marelli, which has 2 coils. That's because it is basically a pair of 6 cylinder distributors stacked on top of each other. A very different setup from the older Lucas twin coil setup.

 

Never mind