Hi all. New to this site. Have been active on the SmokStack forum. I have problems with my 1986 Jeep Cherokee 4 cyl 2.5L with throttle body injection. It just died on the side of the road. Checkout has uncovered no spark. Think it might be the Ignition coil and/or the Ignition Control Module. From what I can find it uses a pickup on the flywheel for timing.

Removed the Coil/Control Module and tried to test it on the bench. When 12 volts is applied to pin 1 and gnd on Pin 2 of the three pin connector of the module, I find 12 volts at the Pin 3. Not sure if that is correct or the module is bad. Also need to know what I should expect as resistance on the primary and secondary of the coil itself.

Also should the pickup sensor show in resistance and voltage during cranking?

Might anyone be able to shed some light on this for me? Thanks Don

 

not sure about the pins, i need to look at a wiring diagram (which you can find in the back of a manual) But the answer to your pulser coil question is yes,to both questions

When cranking you should show resitance when magnet reaches "sensor" (pulser coil) and non when it is not, and as far as voltage, you should be reading about 24 volts ac from pulser if it DOES NOT have a diode or 12.5 volts if it does have a diode. those readings are kinda off, but to get better you must read your manual

another thing to check is take off the distributor cap and check and make sure that the rotor is in good condition, if that is messed up, there is your problem, you wont get any spark from there, and still get readings from your sensors

no matter what get a manual!!!!

let me know!

(sometimes the blonde side gets my memory)

 

Hi Gearheadette. Thanks for your reply. Have two manuals. One Hayes with very poor info or diagrams. And one Factory with a lot more info but no diagrams.

From your statements I am guessing that the pulser coil should have resistance when resting and a voltage pulse when the engine is cranking. Will check that today.

The Ignition Control Module is mounted under the Ignition Coil. When power is applied to the pin 1 of the Ignition Control Module and ground to pin 2, I find that 12 volts is measured at the Tack input (Pin 3). Since this is the pin that should be connected to the pulse pickup module, I did not expect ther should be voltage there.

Also found that there is 12 voltage at the positive terminal of the Ignition control module that connects to the + terminal of the coil. Am I correct that the negative terminal of the coil will be switched by the Ignition Control Module?

My Ignition Coil has very low resistance on the primary winding and under 3000 ohms on the HV secondary to the distributer. Does that sound correct? Rotor and Cap are fine.

All thoughts and suggestions greatly appreciated. Don

 

well, i am home for lunch, i will grab my manual out of my jeep when i get home and take a look and see, but if you have a internally grounded coil, than, yes that is the right reading but if it is externally grounded then no.

i need pics to explain better but there is indeed 2 physical coils inside one "coil" the electricity goes in one, and that builds up ALOT of voltage along with a magnetic feild, and that magnetic field transfers the voltage from one coil to the other, so they aren't technically touching inside there, so unusually high readings are expected, but 3000 is still high for a externally grounded coil.

just remember 2 rules when you start to get frustrated

Ohms law Voltage= Amps x Ohms

and KISS Keep It Simple Stupid!

 

My ignition coil has two windings that I refer to as Primary and Secondary. Primary has the 12 volts applied and is switched by the Control Module. This causes the magnetic field to collapse and induce a Hi Voltage into the Secondary windings, firing the plugs. My Chilton manual lists the primary resistance to be 1.25 to 2 ohms and the scondary from 9K to 12K ohms. I read a bit below 3 K ohms secondary on my coil.
Would like to find out the best way to bench test the Ignition Control Module. After applying 12 volts and ground to the coil, where do I apply, and what do I apply, to the terminal to make the coil fire?

I might be forced to replace both if I cannot do a valid test. Thanks for your help so far. And you forgot the most valid Law--- Murphy's Law. He is a resident at my place. Don

 

I got a 3 step process that will apply to all 84 through 86 XJs that might help you out.

Setp 1, get full coverage auto insurance.

Step 2, pour a gallon of gas inside the vehicle.

Step 3, throw a lit road flare inside and watch it burn.

 

ok, so you fooled me, you know more about the technical aspect than I thought, i am sorry that i was talking a bit condisendingly to you. lol i forget that there are people who actually understand that stuff.

That or you were just testing the level of knowlage of the forum, any who.

WAIT!!! i was just thinking, does your engine just keep cranking and cranking? did you check your crank position sensor???? i forgot about that. if your sensor doesnt work, your jeep definatly wont have spark even if you coil and all that jazz works!

 

Hi Gearheadette. I never thought your posts were condesendingly in any way. Just thought we were using different terms to explain the same thoughts. I really appreciate all of your efforts and welcome all thoughts and ideas from all, no matter how they might appear to you or others.

However I will not take the other posters advice with a match.

While I have a fair knowledge of engines and electronics I do not wish to rediscover the wheel, so to speak, every time I come accross a new problem. If someone else has already found the answer to it, I would rather pick their brain and save time, rather than having to rediscover it for myself after a bunch of tries.

On the flip side I am glad to offer any advice I might have to save others time as well. I do post a lot on the SmokStak forum on Generators and other engines etc.

Your suggestion on the crank position sensor is an area that I had not thought of. Will check it out today.

Once again, thanks for all of your suggestions. Please keep them comeing and if I can help you in any way please let me know. Don

 

Update on my troubleshooting efforts. I measured the Pin 3 of the Diagnostic connecter D1. When cranking with ignition on, it showed pulses. From what I have been reading this would indicate the pickup coil on the flywheel is working. Am I correct?

I also tested the Ingition Control Module on the bench. I applied 12 volts on Pin A and gnd on Pin B pf the three pin connector. I measured 12 volts dc at the right most connector clip that makes contact with the + side of the coil. I also measured 0 volts on the other clip.

I then momentarily applied a positive voltage to Pin C of the same connector as the power was connected. While doing so I saw a positive pulse on the second clip that would connect to the negative of the coil. These measurments were taken with an Oscilloscope, without the coil in place on the Ignition Control Module. When the coil was placed on the ICM clips the positive pulse was no longer there when Pin C was pulsed with a DC voltage.

Also I have not been able to get the coil to develop a HV spark when tested alone. Primary of the coil measures .8 ohms and the secondary 2.89 K ohms. No shorts of either winding to frame ground of the coil.

Would I be right with a guess the coil is bad? And the module might be OK? Thanks Don