If this is like the 1990 dual plug engine I own——
There is a co pack above the exhaust header on a steel base and also one nested down below the intake manifold in front of driver side.
The exhaust side coil is the primary and fires always. The intake coil fires secondarily per RonD, after 400 rpm.
That being said- were the coils NEW motorcraft or Junkyard pulls?
My coils failed due to the heat shield on the exhaust protecting the coil, cracked and fell down, exposing coil to high heat. Already in an abusive location, I welded up the bracket to make the shield work again. That was the root cause of several issues.
I faced a similar situation with both a dead coil driver in the ICM and a dead coil (as mentioned above).
Measuring the coil resistance was key to finding the dead coil pack. Both primary and secondary need tested. Very simple and easy.
Plug and play tell you nothing.
The DVM is your friend.
If you replaced parts in the right sequence, you may have fried parts repeatedly.
I.e., replaced ICM, dead coil in circuit, lost primary ICM (Coil A) driver line.
Replace a coil, now you have good coil and still dead ICM Coil Driver A.
What dies first, the chicken or the egg??
I’ll add this- I was frazzled and testing/trying everything on a miss with a bubba afflicted engine. In the fray, found lots of compounding issues and corrected them. In testing, I miswired a Coil Pack A (primary) and interchanged 2 cylinders. Left Coil B (intake side) correct. New ICM (old one was dead on line B as mentioned prior).
I drive that car 500 miles one day and fought it to 65-70 mph believing all was right. It’s maiden long voyage after repairs. I mean I had exorcised all the demons, literally, from the engine bay, perfecting it all. Except a pair of spark plug wires!
What else??? I made the error!!! And left it that way fully convinced all was perfect.
Secondary coil tried to and successfully made up for the primary miswire except for the elusive POP at every start like a lean POP.
I found my errror when I installed as a matter of course, new wires.
Holy hell. POP magically gone!!!
Bottom line- potentially you smoked a new ICM and it happens frequently hence the warnings on the box, inside sheet, need for heat sink grease and proper screws installed for it on manifold for cooling, etc.
If you have not checked the coil resistance on primaries and secondaries of the coils, you have overlooked a major concern.
my truck had a new aftermarket coil installed on exhaust at start of repairs.
guess what had the 18k ohm secondary???? Should be closer to 12k. A 0.5 ohm primary winding is correct for a good coil and rather on the high side. 0.3-0.4 is more like it.
1 ohm is a dead coil!!
hell 0.8 ohm is dead!!!
So compounding a bad coil was a Dead ICM line in my case.
A DVM and a piercing test light probe was my friend and even a harbor freight LED for high impedance testing of the data lines as if you use incandescent bulbs in some locations, you will fry the solid state.
There is an ignition diagnostic on Ford ICM’s that includes coil output, ground, spout, and diagnostic line testing. Also simple pictorials on coil resistance tests.
I’ll try to find the link and post. I may have posted in a repair thread so search my posts and maybe the link is still there.
BTw- not much of that coil/drive biz will hold a code for you to trace except SPOUT codes.
If it backfires and sputters from say 1500 rpm till about 2500 rpm while accelerating—— well read my posts. ICM failure, coil pack half dead, and messed up wiring feeding ICM and both coils (mid wired spark plug wires LOL)
Every path on that array has to be traced and verified. It’s really sensitive, especially if bubba ever touched your car before you. I even had noise bleeding in causing abhorrent Tach behavior on the ICM wiring (due to bubba).
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