Another motorcraft ignition thread
Need some help troubleshooting my ignition system. Followed Jeephammer's direction in this thread:
With the coil connector disconnected, I get power to the red wire with the key switch in the 'run' position. (test light connected to battery negative terminal)
With the test light connected to the batter positive terminal, I did not get a light on the green wire at the coil connector (with the coil connector disconnected)
Took the new module i bought back and had it tested. It was bad. Exchanged it for another new one, tested it at the store and it was good.
Now I do get a light on the green coil wire, but when I try to crank the engine with the test light on the green wire, the light dims, but does not flash.
Orange and Violet wires on the harness side of the the 4 pin connector read 635 ohms. The 2 parallel wires on the distributor side of the 3 pin connector read 630 ohms.
I have a ground on the distributor case, and the black wire all the way back to the module.
What am I missing?
With the coil connector disconnected, I get power to the red wire with the key switch in the 'run' position. (test light connected to battery negative terminal) IS IT DIM IN RUN AND BRIGHT IN START?
Now I do get a light on the green coil wire, but when I try to crank the engine with the test light on the green wire, the light dims, but does not flash. IF NOT FLASHING THE ICM IS NOT WORKING. IT DOES NOT MEAN IT IS POWERED UP EITHER.
Orange and Violet wires on the harness side of the the 4 pin connector read 635 ohms. The 2 parallel wires on the distributor side of the 3 pin connector read 630 ohms. THAT SUGGESTS THE SENSOR IS INTACT.
I have a ground on the distributor case, and the black wire all the way back to the module. YOU NEED TO TEST THE GROUND AT THE ICM PLUG, DO NOT RELY ON THERE BEING A WIRE IN PLACE, THAT DOES NOT CONFIRM YOU ARE GROUNDING THE ELECTRONICS IN THE ICM.
First of all, congrats on reading JH's posts on the matter, a good first port of call.
You have an ICM that is known to work in the shop but is not doing so in vehicle. You need to check what you have on the ICM plugs, on the harness side.
A word of warning, the shop tests are not always done right. However we can proceed on the assumptin you had a bad module but the new one for some reason is not firing up. Do you have any idea when the old one failed and why?
Look at the 2 pin power plug. The red wire has 12V in both Run and Start. The blue wire (white on ICM side) has 12V in Start only. Check them with the test bulb, you are looking for a bright lamp. If you have no power to the module, you will not get it to switch on and off.
Now check the black ground at the plug. One end on the battery positive terminal, see if you get a Bright bulb when contacting the black wire.
You have already checked the sensors.
Take the distributor cap off and just visually check the sensor is screwed down next to the star shaped wheel on the dizzie.
The only other thing I can think of is it could be a short in the plugs. They get pretty grimy and they can in extreme cases arc. Clean them up as best you can.
I did not check the red wire on the coil in 'start'. Will do that today
I did have a ground on the black wire from the distributor on the harness side of the ICM plug.
I also had power on coming in to the ICM on the red wire on 'run' and blue wire on 'start', but that was before changing the ICM. Should still have power, but I will verify. Did not check power on red wire in 'start'.
Will also check the plugs and sensor inside the distributor today. I loaded the Jeep on a trailer Friday morning on a wheeling trip and left the ignition switch 'on' for a couple of hours. From what I've read, that could have burned up my ICM. Hauled the Jeep ~3hrs to the trailhead and saturday morning no fire. First thought was something rattled loose on the ride until I remembered leaving the key on.
Leaving the key on will fry the coil.
any way to check the coil other than replacing it?
Verified that I have power to the ICM this morning. 12.4V on the red wire switch 'run' and 11.5V on both wires in 'start'
Going to try taking the ICM to a few different part stores to have it tested again
Leaving the key on kills the coil, replace it.
Got it running again. Turned out to a bad icm and a bad coil. I assume they both got burned up when I left the switch on.
Thanks for all the help
yep, they will do that.
good to hear you fixed it.
when you tested the coil power in Run was it a bright or dim bulb? If bright you have no ballast resistor and it may happen again.
It was a bright bulb. where should the ballast resistor be located?
Not sure on your year whether you had a ballast wire or a proper ceramic block resistor or what POs have done to over 35 years. If you follow the red wire back towards the bulkhead you should come across a piece of wire about 4-6" long that has been inserted in the run, this has a resistance. This will be between the coil and a branch in the wire feeding something else in the engine bay such as the electric choke if you had onemor the feed to the ICM.
You may instead have a simple splice where it got damaged and was cut out or some such because it was corroded or burnt out.
If you need to install a new ballast resistor you can buy the wire and splice it in or a ceramic block with two terminals that you can bolt to the firewall and route the wire through.
Your coil should be for a ballasted system. The reason is that during Start it is fed with an increased 12V from the solenoid to boost for the short period of time you are starting but the coil, and the ICM, are not designed to handle the 12V for long periods. Hence you can get problems.
The other thing to check is that the engine is well grounded. The energy from the coil is discharged through the spark plugs to the block and back down the earth strap to the battery. If this is not a good ground route you will find the energy dissipating through the coil, damaging it.
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