Rough Running on '89GT - Bad Coil?

Rough Running on '89GT - Bad Coil?

I have an 89' GT and I think I have a coil going south on me.

Can anybody out there tell me how to "scientifically" test the condition of my coils? I tried to read archived posts but was unsuccessful in getting a clear answer on the proper procedure. Could I remove them and have a shop test them?

The problem can be described as very little available power and real rough engine (like I'm running on half an engine). Problem has seams to be getting worse over the last 3 months but is still intermittent. If the car sits for more than 2-3 days (independent of rain and humidity), without being driven, I have a pretty good chance of the problem showing up within the first 3 minutes of driving the car. Car will usually start-up and initially drive normal before the "problem" arises (although less often start up is sometimes a problem too). Drive down the road and 1/2 to 2 minutes later the engine starts to putter (but never stalls). Shut it down and restart it a half an hour later.... the car runs perfectly. Something about it sitting for 3 days seams to aggravates things. Car is still 99% reliable but I don't want to get stranded or do any engine damage by being in BFE when the problem comes back.

While coils aren't too expansive, I'd hate to start replace a parts that doesn't need it. Car has just been tuned-up (filters, plugs, settings) with no improvement to the problem. The car has about 35K miles on it.

Thanks Folks,

89' GT.

Sounds more like the 89 engine head temperature sensor problem - the location on cylinder 4 and 8 was changed in MY1990 to #3 and 7 because of poor readings which shuts off 1/2 of the injectors. The coils are not a high failure item, the ignition switching unit (two units driverside in front of the radiator) fail more often . Also check the coil wires for poor connections / corrosion. The coil test is terminal 1 to terminal 15 (0.4 to 0.7 ohms) secondary resistance term 1 to term 4 (5 to 8.7 k-ohms).

Jim Bailey
928 International

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