Yeah, the low voltage is a concern. Pin C2 on the ASD relay (upstream on the switch side) ) should see full battery voltage. When the relay closes, you should still see full battery voltage at pin C8 on the relay. This passes through 2 splices (S137 and S109). S109 also sends power to the injectors. You should see full battery voltage at the positive side of each injector (DG/OR wire, same color as the coil.)

If it were mine, I'd pull the ASD relay and check voltage at C2.

The coil does have a positive and negative terminal. The positive should be pin 2 as this one comes from the ASD relay. So this pin should also see full battery voltage when the relay closes (DG/OR wire). Pin 1 (looks like Grey) is the ground to the PCM.

The "piggy back" AWG suggested would be a good next step.

 

have any OBD2 codes been read ?

 

I’ll check the voltage on the 1986 coil, back probed as well as the new OEM with the Power Probe clone. I’ll check OBDII, but no fault code on the dash. Tach is not registering when cranking. I’ll check these things today and report back. Thanks for all the ideas and suggestions. Sometimes a suggestions will stimulate an idea that wasn’t mentioned but grew out of the suggestion. Appreciate all of your time and input.

 

I ran the tests 6/25/23:
Battery showed 12.45 volts on the Power Probe clone.
on the now non-working 1986 coil the OBDII showed a fault code of of P0351 ignition coil A primary/secondary. Read with a basic Autel reader
with the connector on the the coil and a non-LED test light the lamp back-probed and cranking it was lit to equal brightness as the positive battery post. I also measured the cranking volts with Power Probe clone at 10.57 volts (high measurement). I also has a spark tester between the distributor and coil stud, showed no spark. This coil, the 1986 showed spark two days ago.

Measurements on the new OEM MOPAR coil, OBDII showed no fault codes on this coil! With the wiring harness connector on the coil back-probed, a non-LED test light cranking also lit to equal brightness to the positive battery post. The cranking volts on the Power Probe showed a high measurement of 10.46 volts. I had the spark tester hooked up between distributor and coil stud, also no spark.

My uniformed observation and question why is the cranking volts less than 10.5 when the battery shows 12.45? Is this indicative of anything?

 

Saudade, I need clarification on your suggestion to pull the ASD and checking the voltage at C2. Do you do this with the key on. I’m a little gun shy of doing something wrong, just want to make sure I’d do that test correctly. I do appreciate your comment about the lower voltage when cranking though, maybe this is leading the right direction to a solution… I hope.

 

a cheap trick is to pop a length of 5amp wire into a female relay slot, the relay male pin will still fit in nicely and you can easily measure voltage at the relevant relay pin

 

Check page 8W-10-17. Pin C2 on the ASD relay comes direct from the battery through Fuse 18 (25a) so key position should not matter.

AWG's trick is a good one to get the other pin. Otherwise, you'll need to unbolt the PDC to get the back side of the relay socket.

Don't do anything you're not comfortable doing. Just be careful probing around so you don't short something out.

I know you replaced the relay already. Try swapping the relays around. The cooling fan should be the same relay. Again, just tossing things out there.

 

I had a busy day doing non-Jeep stuff, but will try following awg’s and your suggestion tomorrow after cutting firewood. I’ll check the voltage and report back here. I now have the new OEM MOPAR coil installed. I’ll also re-check the primary and secondary resistance on the 1986 coil to see if it’s changed since in no longer fires the engine.

 

I followed awg’s suggestion with the wire under the ASD pin C2; it read 12.39 volts, the battery showed 12.40 volts. There are no OBDII codes present. When cranking the tach does not register anything. I’m following the chart from CCKen on the 99 XJ Ignition Coil Tests… thread— very helpful. I also ran a test requested from the Scanner Danner Forum on pin #2 to the coil with a test light hooked to the positive battery and the pin connected and back-probed. The light flashed when cranked which I’m told shows the control is good. I’m not sure what that means but it was done.

 

so did you make up short jumper wires like I suggested to join the coil and its connectors ?

If making a custom bypass harness, you probably would have to take a lot of care, given resistances

I know it sounds stupid, but I salvage parts of harness just for things like this, you might not ever need them, but if you do, its great, my spare XJ is packed to the gills with spare parts

did you say you live in ****ville and there is no auto electricians nearby ?

An old school auto electrician is what you need to sort this out, as they have the equipment and knowledge

Over here, its an entirely different trade to mechanic, although I think most modern mechanics have more auto electrics training than back in my day

 

awg,

We live on an off-grid ranch an hour away from the small rural town of Lakeview, Oregon, it’s somewhat in the south-eastern part of the state. We have a fine mechanic’s shop but not a specialist at diagnostics. I’m not sure what you are suggesting on the coil connector. I went back looking at your posts and unfortunately, I am not sure what you mean. I have replaced the wiring harness coil connector with a new connector from a reputable on-line source. The OEM connector caused engine stalling when it was wiggled which may have been from the number of times the engine was replaced and the age of the vehicle. We do have a NAPA parts store in town, but they have to order a lot parts, so if I know what I need I look here for information on the best recommendation and try to order myself. Now that we’re stuck without a vehicle it is problematic getting parts out to us, no deliveries to the ranch. I try to reserve calling for favors for really essential things, of course getting the Jeep running is pretty important, I just try to limit calling for help. I know this is a little of topic but it is part of the background.

 

its just such an odd thing,

I am suggesting making and testing a handmade harness with the most basic parts, and testing for connectivity, but if you dont have electronics experience and somewhere to get the little parts, that may not be possible

One reason I ask about auto electricians, is I never seem to see them mentioned on US forums, maybe it is not a separate trade ?

My mate is a very experienced auto electrician, thats all he does 6 days a week 40 years, he would have your vehicle diagnosed in literally minutes

 

Awg,

To the best of my knowledge we do not have a recognized special line of auto electricians. I have another thread on the ScannerDanner Forum. Paul Danner teaches automotive diagnostics, specializing in electrical issues. He says, only about 10% of good auto mechanics in our country are well trained in auto diagnostics. It appears to be more specialized and requires special training to properly use sophisticated, expensive scanners. I mentioned earlier if I knew of a good diagnostic tech within a reasonable distance I would rent a truck and dolly to tow our Jeep to such a person. But, alas I don’t know of anyone within a few hundred miles. If you aren’t familiar with the state of Oregon we are in the Pacific Northwest. Lakeview is small rural town, ranching country, in the past timber was big business; the closest stoplight is 2-4 hours away depending on which you drive.

I am getting some more technical insight on the ScannerDanner Forum, but I’m not sure I’m comfortable doing the suggested procedure. Our mechanic’s father is very knowledgeable on Jeeps, he worked for a Chrysler dealer when they owned Jeep. He is the closest to a diagnostic tech in the local area. He won’t be able to come up to the ranch for a couple more weeks, but I’ll forward the Scanner info for him to consider, he would be comfortable preforming the tests. This is amazing tech, that I’m getting advice from Australia, appreciate you interaction and thoughts.

 

One thing you may be able to try is reach out on your local community Facebook page for any Electronics guys that have an older style oscilloscope

This is the correct tool to diagnose Ignition systems, it would be a bonus if they had auto experience

back in the day, most major service centres had an Ignition Service equipment that included an inbuilt scope, you can pick them up on eBay etc, but they are expensive

I agree that using a scope, new or old, requires knowledge

A guy I know specialised in buying non-going vehicles, fix and re-sell. He was a qualified mechanic and auto electrician

It was often a relatively minor electrical problem

 

It sounds like you have a wire, or splice, that is going bad in the circuit that provides power to the coil. I would use a razor blade to slice off the insulation on the power wire coming from the ASD relay and use an alligator clamp to tap into it with a fused wire attached to battery +, paralleling the ASD circuit essentially. You could also just cut the wire and butt-splice it back together. I understand that not everyone may be comfortable with this.

An alternative is to purchase a harness like the one below. I believe this may work with your XJ, but I'm not 100% sure. This will get you allow you to plug-n-play your way in-between the coil and the wiring.

https://www.holley.com/products/elec...ses/parts/8889