Im sure you have checked this but pre 96 ish the connector pins were round and after they were flat, on almost all of the connectors. Not sure how an 86 connectored coil fits your 97 wiring harness
awg, & bluejeep2001 I looked at the Hantek scope, that is a piece of equipment that looks well beyond my skill-set. Use of a scope like that is may be second nature to a number of members, my learning curve would take me a long time to master even the basics. I am somewhat comfortable with using a basic digital multimeter to check volts and ohms. Beyond that it would be time for YouTube training.
Regarding the coil pins on the 1986 coil it does have round pins; I call it 1986 due to the stamped date in the same font under the stamped part number, there is no brand name visible. In looking at RockAuto I noticed on a number of earlier year XJs that the coils offered, had both round or blade connectors. Visually the pin diameter on the 1986 appears to be identical to the brand new OEM MOPAR. Because the pins are recessed in the female connector my basic digital caliper can’t reach in there to accurately measure the pin dia.
When researching the number on the 1986 coil, the part number 56027966 is only listed on-line as a used part, interestingly most of the offerings are in the UK eBay, there were one or two used ones with that number on US eBay. At this point I am not rushing to buy another old coil — I doubt if another old coil even with the exact part number would work.. When entering that number in RockAuto the number 56027965 comes up for a 96 Grand Cherokee as the part number to use. That is the recent part I purchased, it was less than $20. It did not fire the engine and I sent it back.I am still hoping to find out why the spec’d new OEM doesn’t work when the 1986 does. I do appreciate you observations and suggestions.
bluejeep2001, attached are a picture of the PCM to coil connector as well as the pins of the new MOPAR coil. This connector is new from Summit Auto. The new connector was installed due to a stalling of the engine when the wire at the connector was wiggled. I added extra length to the wire when soldering the new connector as I felt the OEM wire length was a little tight in connecting to the coil.
A little additional information: I have also opened a thread on Scanner Danner’s Forum and one the questions was a check on distributor to coil spark testing. Using a Lisle 20610 tester between the distributor and coil the 1986 coil sparked very bright. The two OEM and NGK coil showed absolutely no visible spark. Obviously, therein lies the problem the $64,000 question is why?
make up two connector wires to go between the male and female connectors pins, even as simple as scrunched up copper wire, see if that makes the connection work
takes a few minutes, cost is zero
the answer has to be something simple if the coils work on other jeeps
Had a busy day with other projects today, tomorrow will be another Jeep day. I think, if I understand you correctly, you are suggesting to make a jumper set to change the polarity from the connector to one of the new coils. Is that correct? I’ve been cautious of doing that for fear of somehow damaging the coil. However, because it is clear with no spark at the coil I’ll risk trying that with the NGK coil. I asked the mechanic if somehow something with the new distributor and cam sensor could be causing this issue. He didn’t think so, I’m trying to understand how the 1986 coil gets spark but the newer ones don’t.
In my lack of knowledge I asked if somehow the 1986 might have reversed polarity and the new ones don’t. I’ll try the jumper to reverse polarity tomorrow to test this idea and report back. I’m pleased with the over 600 views now and hope perhaps one you will have the idea that leads to the solution to this XJ mystery.
I’ll try the jumper to reverse polarity tomorrow to test this idea and report back. .
Hmmm...I wouldnt do that unless you get an all clear from someone else on here
The PCM provides earth, so connecting the coil with incorrect polarity may have bad consequences (it probably should be ok)
As to the jumper wires, as long as you are careful, it will be ok, just dont short them, scrunched up alfoil is of use in female connector pins to establish electrical continuity
I am a technician, and have made piggyback jumper wires to test my hypothesis in many situations
Had a problem with windows, made a piggyback jumper wire, now works fine, something in the OEM wire is defective
hen I mentioned this on here, a fellow piped up, saying he was an aircraft maintenance tech, and they made piggyback jumpers often
Awg, your comments have caused me to hold off on trying to reverse polarity until I feel confident someone that seems to know what the ramifications might be says to try that. Thanks for your caution yellow light… because I have a the same thread on the Scanner Danner Forum I may be guilty of repeating myself. There was the suggestion there as well to try reversing, but I wasn’t sure on the knowledge base of the person making the suggestion. The last thing I want to do is make this situation worse.
One of the mechanics had me identify which pin in the coil connector had 12 volts with a back-probe. That was pin #1 which is the pin closest to the engine block when the connector with the back-probe is plugged into the coil. With the 1986 coil installed the voltage read, 13.95-14.08 volts with the engine running.
I then installed the new OEM MOPAR coil, with the engine cranking—no start, it read 10.56-10.70 volts. The question is what is causing the voltage drop to the new OEM and not to the 1986 coil? I used my Chinese Power Probe clone to measure the voltage.it was the easiest way to reach into the back-probed t-pin.
I’m waiting for the mechanic to be able to respond to this new data, and I’m hoping perhaps one of you may have an idea(s) to this mystery.
Well, first this is an "apples to oranges" comparison. You'd expect to see 13-14 volts with the engine running and just battery voltage with it off.
However, the coil gets power from the ASD relay when energized. The coil is grounded through the PCM. So you should see battery voltage with the engine off, key on/start.
"IGNITION COIL (page 8W-30-38)
When the Automatic Shut Down (ASD) relay contacts close, they connect circuits A16 and A142. Circuit A142 splices to supply voltage to the ignition coil. The Powertrain Control Module (PCM) controls the ground path for the ignition coil on circuit K19. Circuit K19 connects to cavity A7 of the PCM."
Page 8D-6 has a procedure for testing the coil.
Page 8W-80-53 shows the pinouts for the coil. Looks like Pin 2 is the ASD output and should have 12 V. If you measure at Pin 1, I'd expect to see something less than battery voltage since you have the coil acting as a low ohm resistor.
Are you sure your battery is fully charged?
Again, just throwing things out there to see if we can get to the bottom of this.
Saudade,,
I guess this is one of the areas where my lack of knowledge shows through. I thought the cranking volts on the new OEM and the running volts on the 1986 should be the same. I thought somehow this showed the problem. When I saw the difference I thought that we were a step in the direction of defining the problem; a wise man taught me that a problem defined is a problem half solved—I was hoping we were on the road to a solution when I saw this difference. Regarding the state of the battery, it was 12.65 volts measured with the Power-Probe clone. Thanks for the input,
Well, you could compare to the "old" coil. Pull the fuel pump relay (so it doesn't start) and crank it over while back probing.
You said earlier that the mech measured the resistance of the 2 new coils and both were "in spec". Do you know what the actual measurement was? Page 8D-6 shows ignition coil resistance to be 0.95-1.20 Ohms on the Primary and 11,300-13,300 ohms on the secondary.
Regarding resistance numbers: I posted these results on the ScannerDanner Forum, I thought I had posted these numbers here as well. Sorry about that here they are. I was asked to test the resistance to both pins. Resistance numbers: I tested the resistance numbers following a chart from the Cherokee Forum on how to test resistance combined with the suggestion here to record the values for both coil pins.
Primary Resistance Secondary Pin 1. Pin 2
1986. Coil. 1.0 ohm. 12.23 k ohms. 12.23 k ohms
5/2020 OEM Coil. 1.1 ohm. 12.96 k ohms. 12.96 k ohms
8/2022 NGK Coil. 1.1 ohm. 12.36 k ohms. 12.36 k ohms
6/2023 OEM Coil. 1.0 ohm. 13.21 k ohms. 13.21 k ohms
These numbers are with the specs from the chart that was posted on this Forum.
We had to go to town yesterday and chores this morning. I’ll try later this afternoon to check the cranking volts on both by pulling the fuel pump relay. It would be interesting to have that comparison with apples to apples. I still wonder why the cranking volts on the OEM was only 10.56-10.70 volts when the battery showed 12.65 on my power probe clone. To my untrained thinking that seems significant. One thing that is a concern, the last two times I’ve swapped out the 1986 coil for testing it didn’t want to start on the first turn of the key … it did fire on the second try but with our situation that is a concern. If I lose the 86 coil we’re are literally stuck up the creek without the proverbial paddle.
Well, I tried testing the 1986 coil and the new OEM with the fuel pump relay pulled to measure the cranking volts in what was said to be an apple to apple test. The battery measured 12.51 volts with my power probe clone.
1986 coil- cranking only 10.60-10.76 volts
2023 new OEM coil- 10.65-10.80 volts
they are virtually the same with one giant problem, now the 1986 coil will not start the engine—we are dead in the water, up the creek without a paddle, at least the Jeep is in our garage and not stranded somewhere on the highway or on the 12 miles of dirt road to the ranch. Our mechanic is out of town this weekend so I’ll have to wait to see what he suggest next… unless someone has an idea on the forum for me to try.
