What should I be checking for ? Voltage , resistance? With a dvm or test light ? Does it specify ?
No spark from new coil #3 but fine on #6
- Thread starter Jdad
- Start date
You could have a damaged/pushed pin or corrosion on the PCM side causing a short or something.
That the new coil worked for an hour or so before failing like the old one I bet something is whacking the internal coils of the coil pack.
That it's the same one is peculiar and may just be a coincidence, or maybe the physical internals result in #3 always getting hit in that pair....I dunno.
It is a bit of a head scratcher for such a simple circuit.
My background is in avionics, not vehicle mechanics, but whenever I'd see a new replacement part fail in the same way as the replaced failed part, I was usually looking at a short or bad connector.
I'd just disconnect both ends and check for damage, maybe ohm it out end to end and see if it's shorted to ground.
I've only had my JK for a couple years, and I'm no mechanic, so I'm still learning this stuff too even though I'm no stranger to wiring diagrams and electronics in general.
No idea what would cause a single signal on one wire going to two coils at the same time cause only one of them to fire other than physical internal damage to one of the coils.
The shop doesn't have an opening before next Friday so more testing to be done. I only had a few mins to check things today before dark and this may make me stupid but where is c2 on the pcm ? Is it the second connector from the left ? It was getting dark so I couldn't see anything labeled c2. I have found some wiring diagrams for an 07 but I'm not sure I'm reading them correctly. Where some of the wires end it says where but some just have numbers and doesn't say what it is. Very confusing to me
Sorry brother haven't checked in for a day or two.
If memory serves, looking at the back of the PCM, they're 1-4 left to right. (driver side towards pass side)
If I get some time I'll dig through the manual and double check.
I ohmed c2 pin 7 to coil connection and it was ok, had 0 resistance. Anyone know how the pcm is grounded ? I found 1 ground from the case to fender , is that it ?
You've got a real one here, that's for sure.
Only other thing in the circuit that could affect the coil is the ASD relay, but if that was the problem it wouldn't run at all.
What makes zero sense to me is you have one wire to/from the PCM that controls two coils, and only one of them is not firing. When you replaced the coil pack, it actually worked for an hour or so if I remember correctly. That sort of problem indicates being damaged while running, and there's not much in the system that could do that.
Did you replace the wires/plugs before or after you swapped in the new coil pack?
Ah ha ! When I tested the old coil and had no spark from #3 I replaced the coil and it worked for an hour then same no spark. I THEN replaced the wire and plug ! I have since gotten a new coil again but I'm afraid to put it in and have the same issue. I forsee a problem trying to return another coil for replacement at the parts store. Should I just say f__k it and try it since I replaced the wire and plug ? The old wire and plug dawned on me today as I was doing some testing. They were the only common things to both old and new coil. I checked pretty much everything except driving down the road to see if it's a loose wire but that's hard to test. Lol
Another thing is I ohmed all 3 coil packs primary and secondary circuts and they all were very close in readings. Nothing was far off other than not getting spark from the old one and the first new one after an hour. Primary was .6 to .7 ohms and secondary was like 11.7k to 12.1k on all posts on all coils. The new one I got that has not been hooked up yet ohms to the same
Well a plug/wire can damage an ignition coil, so if it was me I would do it.
There's not much here that could damage the coil, and the plug/wire are the most likely causes.
At worst you're out the cost of the coil, but if it fixes it, you'll be saving a lot in shop fees.
Vman should change his name to THEEman. I tested everything humanly possible and it all checked ok so I put the new coil in with new wires and plugs and all is good so far. Idle and test drive a success. Thank you for the diagrams and me being able to bounce things off of a knowledgeable someone. Happy new year to ya from the east coast ! If something happens with this is the near future I'll be back. 
Vman should change his name to THEEman. I tested everything humanly possible and it all checked ok so I put the new coil in with new wires and plugs and all is good so far. Idle and test drive a success. Thank you for the diagrams and me being able to bounce things off of a knowledgeable someone. Happy new year to ya from the east coast ! If something happens with this is the near future I'll be back.
Outstanding! I'm glad everything is working out for you brother, and happy new year from the snow covered north west.
Been out today testing out my trutracs and playing in the snow so glad to hear you got your rig back on the road too.
