Over the past couple of weeks, my 85GT began riding extremely rough at cruising speeds of 45-50mph. It felt like a miss but would idle and drive on the highway just fine. Last Wednesday, whatever it was finally croaked because I was running an errand and the car just DIED. Engine shutoff and never restarted. It will crank just fine but never turns over. After researching in the archives, here is what I've done so far:
1) I can hear the full pump run and smell fuel after trying to start it a few times so skipped past any lack of fuel possibilities. 2) I observed the tach go up to ~400rpm while cranking so was hopeful ICM was good. 3) Used a test light and confirmed I'm not getting spark. (I checked at the number 1, 3, and 5 spark plug as well as the ignition coil to the distributor. No spark anywhere.) 3) I pulled the ICM and took it to Autozone for testing. They confirmed it was BAD. So, I decided to replace it with a whole new distributor because the extra work to do so was so low. (I had Autozone test the new ICM just to make sure and it passed.) 4) I installed the new distributor/ICM using the markings I made with the old to avoid messing up the timing. I even installed all new spark plug wires.
After all the above, the car behaves the same. It cranks but will not turn over. With my test light, I see I'm still not getting spark off the ignition coil. So, my question is is it possible my ignition coil is bad too? Can a bad ignition coil cause a blown ICM or vice versa? I just wonder if there is anything else I should check before buying more parts?
So, my question is is it possible my ignition coil is bad too? Can a bad ignition coil cause a blown ICM or vice versa? I just wonder if there is anything else I should check before buying more parts?
Thanks,
Yes! Bad Ignition coils can wreck an ICM. They can be easily tested, and are not expensive. Don't get a fancy one......get a stock replacement.
[This message has been edited by Gall757 (edited 07-20-2020).]
Thank you, that document is perfect. I removed my ignition coil and tested it according to those instructions. Step 1 and step 2 check out perfectly. Step 3 measures 4.73k. Is there a range this should fall into? Not equal to "open/infinite" leaves quite a few possibilities. The only ones I have to compare to are others on Youtube. One measured 8.8k and was deemed good while another was 3.7k and deemed bad. I'm guessing mine is bad being closer to 3.7k than 8.8k but wonder how widely it varies. If it matters, mine is an MSD ignition coil from the previous owner. Thanks,
Got online last night to buy new ignition coil and found the specs for the ignition I currently have. (MSD 8226) It says the secondary resistance is 4.8k... so now I'm not so sure the coil is bad.
You have a MSD ignition coil? Do a little searching about that and you may want to get rid of it. MSD coils run a higher voltage through the components, and some components may not be up for the abuse. Unless your whole ignition system is MSD, I would recommend going back to a stock coil. The MSD also may be the reason for your ICM problems.
[This message has been edited by Gall757 (edited 07-21-2020).]
The symptoms described in the OP are typical of a faulty ignition coil. Stock replacement coils are pretty affordable. Plus it's good to have a spare, just in case.
Also note that if the coil doesn't fail the multimeter test, that doesn't guarantee it's good. But failing the test does guarantee it's bad.
Gall - Yes, the previous owner had MSD ignition coil AND distributor. However, my replacement distributor was not MSD. I wasn't aware of the differences until researching this problem.
I replaced the MSD ignition coil with a standard OEM replacement and it fired right up... all is well again!
Thank you all for the help and information. On to the next gremlin...
No problem. I only mentioned it as it's amazing how often established members also fail to mention the year or the engine or anything about their Fiero when asking for advice. It's like we're supposed to remember from the last time they asked for help.
No problem. I only mentioned it as it's amazing how often established members also fail to mention the year or the engine or anything about their Fiero when asking for advice. It's like we're supposed to remember from the last time they asked for help.
We ARE supposed to remember!
For example, you have two Fieros... a 1984 with the lower trim and a 1988 Formula!
