1997 XJ, new Jasper 4.0L engine. The problem is no start with new OEM MOPAR ignition coil. Mechanics are stumped, on a lark they tried an old used coil that is stamped “1986” under the id number, no brand is shown and the Jeep starts and runs fine. Put the correct OEM MOPAR coil or an NGK and cranks but no start. Any ideas why it runs on an old coil that has primary resistance of.8 ohms with secondary resistance, cold, at 12.9k ohms but the new MOPAR or NGK won’t work? Wrenching beyond basics is not my skill-set and with the shop mechanics stumped I’m hoping perhaps someone here can lend some insight on what to do. Also since putting in the 1986 coil we’ve lost the OBDII communication, is this related? Putting in the new coil does not restore OBDII communication. We live on a remote ranch and this is our only vehicle, any ideas will be greatly appreciated.

Found broken ground wire to the OBDII, have communication back, that’s good. Checked if the new OEM coil would now work, still won’t fire.. A little more information on our Jeep. Every sensor and relay has been replaced, the CPS with an OEM. Fuel pump and distributor are new, fuel pressure is within spec. In ignorance I’ve been guilty of throwing parts at the problem - I’ve justified that with the vehicles age.. Of course the old coil stamped 1986 fires and runs the Jeep. The old coil part number has been superseded with 56027965 (the coil is stamped 56027966) in desperation I’ve ordered a new 56027965 from Rock Auto, the part number is listed as being used in a 95-96 Grand Cherokee. My concern is, how long the old used coil stamped 1986 will last, if it goes out, we’re dead in the water, the mystery is why new coils won’t work. A year ago I had a fault code on the coil, at the time I could only get a NGK. The NGK fired the Jeep but it would stall intermittently, eventually wouldn’t start. The mechanic has tested the NGK and new OEM, the primary and secondary resistance is within spec… a friend has suggested a can of gas and road flare would fix the problem, I suspect that would be difficult to claim on the insurance. This is a very nice XJ, 2” lift, aftermarket bumpers, winch etc, never wrecked - no rust. Any ideas besides the gas can …

This is update #2 in our on-going saga for the 97 XJ coil. Received the new RockAuto replacement coil number for the old 1986 coil that runs the Jeep. The new one cranks but no start. Put the 1986 coil back in and it starts fine. As mentioned earlier this is our only vehicle and we have to be able to get to town from our remote location. I’m hoping that someone on the Forum will have an idea as to why an old coil works but a new OEM MOPAR or the NGK won ‘t fire the engine. We thought at one point that the PCM might be the issue. Bought a used PCM that came out of a running vehicle, it has the correct numbers for this XJ, which runs the Jeep but doesn’t solve the coil issue. We later found out from the mechanic’s scan that replacement PCM was out of a 2 wheel drive vehicle, so we’re running the correct 4 wheel drive PCM. I’m not sure what difference the 2-wheel drive PCM vs. 4-wheel drive PCM would make and was disappointed to learn that even though it had the correct number it wasn’t for a 4-wheel drive, another lesson in living with a 26 year old Jeep.

A note on the OBDII grounding issue. The ground for the OBDII is ground #102 by the oil dip-stick. What happened was the ground wire(s) had pulled away from the ring connector but we’re covered by the heat-shrink. Everything looked good but there wasn’t grounding contact to the block which was why we had no OBDII communication. Another lessons learned about grounding.

I appreciate each member that has read this thread and continue to hope that someone will have an idea why the correct OEM coil won’t work but one stamped 1986 does. This is a very nice XJ with only 150,568 miles on it. I regularly get compliments on the build. There is just one little bitty problem, it’s not reliable. I’m retired so I check the Forum often during the day hoping for an idea that leads to a solution. Thanks for your time.

Update #3…

Spent some time yesterday studying the differences between the 1986 coil and the two OEM and NGK coils. I carefully measured the connecting stud the distributor/coil wire attaches to; I also measured and noted the size of nipple grove on the end of the stud. Next, I measured the depth of the boots on the distributor to coil wire thinking perhaps a difference in the boot depth might be the reason the new coils won’t work. The stud and nipple grove measurement difference were very minor. The boot depth difference between the Bosch and “Premium Lifetime Napa” wire set was the greatest. That difference gave me a fleeting hope that perhaps I had found the smoking gun to the problem.

Another cautious hope dashed on the rocks; I can’t tell you how often that has happened in this on going patience-building process. When swapping the coils around only the 1986 would start and run the Cherokee. I did have an observation from my measuring, the 1986 coil does not have a brass connecting stud like the other coils, it’s aluminum. I don’t see why that should make a difference … but it is a difference. Oh how I wish there was a Scanner Danner or Eric the car guy in my area. I need someone who is a wizard at diagnostics, unfortunately not in our area. Lakeview is a small rural town in the south east corner of Oregon; how small? The closest stop light is 2.5 -4 hours away, depending on which way you travel.

While cutting fire wood the other morning I was reminded how some times trees “accidentally” fall on vehicles totaling rigs, it does happen in our area of the woods. That solution falls in the original gas can and road flare suggestion. While the temptation to be dishonest raises its ugly head … I can’t and won’t go there. There has to be a logical explanation to this dilemma. I wish Eric or Danner had the time to answer my emails. It was lawsoncl’s post that gave me the idea to measure the stud and boot, still hoping someone on the forum may have the idea that leads to the solution. I do appreciate the 250+ views on the forum…

 

Opps… my mistake put the Update #2 in the wrong place.

This is update #2 in our on-going saga for the 97 XJ coil. Received the new RockAuto replacement coil number for the old 1986 coil that runs the Jeep. The new one cranks but no start. Put the 1986 coil back in and it starts fine. As mentioned earlier this is our only vehicle and we have to be able to get to town from our remote location. I’m hoping that someone on the Forum will have an idea as to why an old coil works but a new OEM MOPAR or the NGK won ‘t fire the engine. We thought at one point that the PCM might be the issue. Bought a used PCM that came out of a running vehicle, it has the correct numbers for this XJ, which runs the Jeep but doesn’t solve the coil issue. We later found out from the mechanic’s scan that replacement PCM was out of a 2 wheel drive vehicle, so we’re running the correct 4 wheel drive PCM. I’m not sure what difference the 2-wheel drive PCM vs. 4-wheel drive PCM would make and was disappointed to learn that even though it had the correct number it wasn’t for a 4-wheel drive, another lesson in living with a 26 year old Jeep.

A note on the OBDII grounding issue. The ground for the OBDII is ground #102 by the oil dip-stick. What happened was the ground wire(s) had pulled away from the ring connector but we’re covered by the heat-shrink. Everything looked good but there wasn’t grounding contact to the block which was why we had no OBDII communication. Another lessons learned about grounding.

I appreciate each member that has read this thread and continue to hope that someone will have an idea why the correct OEM coil won’t work but one stamped 1986 does. This is a very nice XJ with only 150,568 miles on it. I regularly get compliments on the build. There is just one little bitty problem, it’s not reliable. I’m retired so I check the Forum often during the day hoping for an idea that leads to a solution. Thanks for your time.

 

I thought maybe a crossover year issue, but the FSM for 96, 97, and 99 all show the same primary and secondary nominal resistance values of ~1 ohm primary and 11-13k secondary. New coils need grounding through their mount somehow? Is is possible the coil wire isn't seating correctly on the correct coils?

 

That’s a great and valid question … the coil/distributor wire is a new Bosch set. Every time different coils have been swapped out, when replacing the distributor coil wire I can hear and feel the boot click on. Your question will cause me to pull the coil and actually measure the coil to boot stud, I’m not sure what that part of the coil is called. I have a set of wires before the the new Bosch set , I’ll try a different distributor to coil wire in case somehow the Bosch wire to coil is the issue. The PCM wire connector in the main wiring loom at the coil was replaced with a Summit replacement connector. The original connector caused a stalling when wiggled. The new Jasper engine was installed in November of 2021. We began having an intermittent stalling issue in late July of 2022. The stalling increased in frequency until late December of 2022 when the engine would no longer start. That’s when the mechanics tried the old 1986 coil he had in a parts bin. He has no idea where he got it or what it was from.

The 1986 coil was attached to the block bracket that is identical to the 1997 coil to block bracket. I assume the 4.0 engine in Wranglers and Grand Cherokees used the same mounting bracket, perhaps even other Chrysler engines. Because of our remote location the mechanics actually has made “house calls” 3-4 times since we’re stranded without an operating vehicle. Our mechanic and his Father were founding members of the local off-road Jeep club.

I tried running a new wire from the PCM connector to the coil; thinking perhaps the wire somehow was degrading the current flow. That didn’t change a thing. The 1986 coil still worked and the new OEMs (I have two OEM MOPAR coils) and the NGK didn’t. I resoldered the original wiring back. The coil to block mounting bracket has been cleaned to bare metal as well as the the block grounding point; every ground point, including in the rear of the Jeep has been cleaned to bare metal. I greatly appreciate your input and the time you spent in considering this situation. Why the old coil works and new ones won’t is a mystery. I keep thinking there has to be reason that we’re missing.

 

Braided ground strap from engine to firewall?

Have you added a wire from the battery negative to the inner fender? And one from the dash to the body?

 

Jim,
The cables have been upgraded from JeepCables.com back around 2018. I have checked all grounds to bare metal Thanks for your question. I do appreciate input and questions. We had to go to town today, so I wasn’t able to check on the distributor to coil wire and measuring of the coil connector/stud between all the coils. Tomorrows project after cutting off firewood. Thanks.

 

Update #3… Posting as a reply so folks see this update

Spent some time yesterday studying the differences between the 1986 coil and the two OEM and NGK coils. I carefully measured the connecting stud the distributor/coil wire attaches to; I also measured and noted the size of nipple grove on the end of the stud. Next, I measured the depth of the boots on the distributor to coil wire thinking perhaps a difference in the boot depth might be the reason the new coils won’t work. The stud and nipple grove measurement difference were very minor. The boot depth difference between the Bosch and “Premium Lifetime Napa” wire set was the greatest. That difference gave me a fleeting hope that perhaps I had found the smoking gun to the problem.

Another cautious hope dashed on the rocks; I can’t tell you how often that has happened in this on going patience-building process. When swapping the coils around only the 1986 would start and run the Cherokee. I did have an observation from my measuring, the 1986 coil does not have a brass connecting stud like the other coils, it’s aluminum. I don’t see why that should make a difference … but it is a difference. Oh how I wish there was a Scanner Danner or Eric the car guy in my area. I need someone who is a wizard at diagnostics, unfortunately not in our area. Lakeview is a small rural town in the south east corner of Oregon; how small? The closest stop light is 2.5 -4 hours away, depending on which way you travel.

While cutting fire wood the other morning I was reminded how some times trees “accidentally” fall on vehicles totaling rigs, it does happen in our area of the woods. That solution falls in the original gas can and road flare suggestion. While the temptation to be dishonest raises its ugly head … I can’t and won’t go there. There has to be a logical explanation to this dilemma. I wish Eric or Danner had the time to answer my emails. It was lawsoncl’s post that gave me the idea to measure the stud and boot, still hoping someone on the forum may have the idea that leads to the solution. I do appreciate the 250+ views on the forum…

 

Forgive me if this was stated in your earlier posts and I overlooked it. Did you actually verify spark at the plugs AND at the center post for the cap with the new coils?

I see you measured the resistance of the primary and secondary coils. Did you check to see if the primary is shorted to ground? The coil's secondary grounds when you bolt it to the bracket (or course, the other end at the plug). Given the new paint/coating on the new coil, are you sure you're getting a good ground on the secondary?

Look carefully at the connector pins of the old and new coil, then look carefully in the connector. It's possible one or both pins on the new coils are not making contact.

I just tossing stuff out there.

 

I know the mechanic and his father, who worked for Jeep when owned by Chrysler checked the spark on the 2020 MOPAR and NGK coils. They also took both coils into town to check in another Cherokee, they both tested and ran the test XJ. The 1986 coil runs the our vehicle really well, the concern is for how long? A 37 year old coil might run 10 years or stop next week. Wherever or whenever it stops without a replacement were stuck. At this time only driving when we feel it’s essential.

I’ll have to do some YouTube studying to check how to test the secondary ground you mentioned. I’m a retired pastor who is more comfortable swinging a hammer building a house than wrenching under the hood, not my skill sets. They say, “Necessity is the mother of invention” it also a great motivator to learn new skill when necessary. Thankful for this Forum and YouTube.

A little more background on this Jeep: this is the fourth engine. Engine #1 OEM, engine #2 was a rebuilt at 95 k when the original owner didn’t check the oil (we bought the Cherokee at 100k in 2013), engine #3- Jasper #1 which was replaced by the shop under warranty due to some failure, engine #4 is Jasper #2 which is currently in the Jeep. Engine #2, the rebuilt engine failed in 2021 with 3 cylinders losing compression. That’s a lot of in and out of engines on the wiring harness. We thought when we were experiencing intermittent stalling that wiring was the issue. I opened all the loom checking the wires. They were soft, not cooked at all and very pliable. Re-tapped and new loom installed. I was amazed that 26 year wires looked so good. While trying to find when the stalling was the issue we discovered the coil to PCM connector was a problem when wiggled, it would cause a stall. That was replaced with a Summit connector.

I’ll do a visual inspection of the coil pins, I’ve looked at the pins but not carefully comparing them, I’m not sure how I would spot a difference unless it was a major issue. I know the 2020 OEM and NGK test within spec. I learned how to test the primary and secondary resistance from a page posted on this Forum. Plus the mechanic tested them in town and ran another Cherokee with them. I have checked continuity on all the wires from the PCM to the coil, and all the sensors as well.

I do appreciate you ideas and will try to follow your suggestions. To borrow from an old tv show, “XJ Files … where is the answer?” I suspect the answer will end up being something simple that’s why I appreciate every suggestion to look into.

 

Well, I think this is very odd.

First, I misstated about the grounds. The coil does not ground through the mounting. Still the fact that the new ones work on another Jeep confirm they're good.

So we know the parts are good. The only difference is the connection. Sometimes the pins wear in the old connectors, or can spread a bit. It *might* be the old coil makes better contact. The new coil *may* have smaller pins to save costs, and therefore isn't making the proper contact. Who knows!! Again, just throwing things out there.

I realize how frustrating this must be for you, especially given the history.

 

I love a good mystery, but only when I have time to enjoy it versus stuck along the side of the road.

 

Saudade and lawsoncl, you both have hit the nail on the head regarding both the mystery and frustration. With the local shop stumped I’m still hoping that someone on the Forum will have an idea that solves or leads to the solution. When the 1986 coil ran the Jeep, we debated spending the extra money to try another new OEM MOPAR, they are $200 on Rock Auto. After thought we decided that if that solved the issue it was money well spent. Even though I’m not a wrencher or shade tree mechanic I try to take care of our vehicle and have made a number improvement mods, when it was running. From 2013 to the demise of Engine #2 in 2021 it served us well. We have Truck Tracks, for turning the XJ into a snow-cat so we can get off the mountain in the winter in deep snow.

The challenge is what do we do next? We would consider trying to get it to another shop within a couple of hundred miles if we knew of a good diagnostic shop. I understand diagnostic shops are a very small percentage of what might be good reputable parts changing shops.

I still hope with the number of Cherokee owners on this Forum someone will have solution to this XJ File’s mystery. The challenge is open to all…

 

If they are measuring the same, I feel like it's just gotta be a connection issue. You tried measuring further upstream? Like measuring the secondary resistance from the coil wire at the cap or backprobing connections on the primary side?

 

I have checked continuity of the wires from the coil and Automatic Shutdown Relay to the PCM, In trying to follow a wiring diagram I saw that the ASD was involved in controlling the coil. I pulled the relay and checked the continuity of each pin slot for the relay to the PCM. I did use back-probing on the PCM with a T-pin. I haven’t tried measuring resistance on those wires.

We have a snorkel installed to help with dust on the 12 miles /dirt road to the ranch. It takes a little work to pull the air box to back probe the PCM due to the mods for the snorkel. I also have a PSC power-steering upgrade pump with remote reservoir which makes a tight fit for the air box. The power-steering upgrade was needed for the winter tracks which destroyed the OEM power-steering pump. The pump and snorkel mods were necessary for our application.

I won’t have time to disassemble until sometime next week. But this is probably worth investigating. Anybody know what kind of resistance a back-probed wire should show? I assume I would just back-probe the correct PCM pin and the same wire at the coil connection— with a digital meter set to ohms, anything I’m missing on this? I totally agree that the issue seems to be some electrical connection but don’t know what to check.

When we were experiencing intermittent stalling I thought perhaps the problem was with the PCM. That’s when I bought a PCM which I later found out was for a 2 wheel drive Cherokee. I’ve tried both PCMs with the same results that only the 1986 coil fires our Jeep.

 

as far as I know, the correct way to diagnose an ignition system is with an oscilloscope.

I remember, and you can see on Youtube no doubt, I think they are called SunTech, big old machines

These days simple automotive digital oscilloscopes are inexpensive

There is a poster on here that uses the Hantek scope