Geordo`

first time caller, long time listener. er. been reading the forums as needed for various issues, but finally need to make a post.
I have posted the story on another forum, so if any of you also read that one, this may be old news. haha.
the short story: misfire in cylinder 2 in december after running fine and no mechanical issues on the engine other than eating oil, threw parts at it in my shop, while limping it to and from work (plugs/air filter/pcv/coil/wires/seafoam) got worse. trailered it to a mechanic I trust, new throttle body, new pcm, new rebuild engine - twice (i'll elaborate below), replaced pcm, ignition wiring harness and all sensors, misfires have moved to cylinders 1,3,5 at random. jeep is an 07 jk unlimited, standard, currently at about 180k.
the long story::
last December, I developed a misfire on my way to work, in about -20C. Jeep was plugged in (block heater, battery blanket) after about a 10-15 minute drive to work, it threw the code. generally I get it up to temperature halfway through the drive. i had the dealer read/clear the code at lunch, and limped it home. Drove jeep to/from work for about 4 more day (dumb i know) with misfire getting worse and losing power gradually. misfires seemed worse at lower rpm, but could be anecdotal. while driving to/from work, picked up and replaced wires/plugs. didn't better. double checked plug gaps, replaced crank position sensor, ignition coil, cleaned throttle body, changed air filter, pcv valve, cleaned and checked engine grounds, cleaned intake manifold, seafoamed each cylinder, did a smoke test for vacuum leaks, and swapped the asd relay to rule that out. nothing worked. when i pulled battery (quite new due <6 months) and started it again, it would run it's best for about 30-45 seconds and read misfire. as some point the throttle light came on, and would go away. clearly i'm making it angry. i trailered it to a trusted mechanic. we has been fighting with it since.

I will have definitely forgot the order and the details of the issues, but throttle body, plugs/wires again, camshaft sensor, map sensor were replaced next. lost compression in one cylinder, and it was blowing by the rings bad. I live in a city, but it's very isolated. one company owns both machine shops and they spit at you if you mention re machining a 3.8L. at some point mechanic took temperature readings on the cats and they seemed fine. My mechanic talked to a jeep guy in victoria BC who rebuilds, focusing on the weak points on the 3.8 and provided a 160,000km warranty. I went ahead with the rebuilt. still misfiring.injectors replaced, pcm was next. i can't recall if it was new or used, but the stealership had to reprogram the replacement pcm. something worth noting is that when the dealership has their computer hooked up for the reprogramming it ran great, no issue. but the misfire returned when the computer was disconnected. if i recall correctly, the misfire became more intermittent, and the mechanic had to drive it for about 10 minutes to get the misfire. as some point the new engine started running like garbage again, showed a loss of compression or something to that effect and was replaced under warranty. new rebuild was still misfiring. ignition wiring harness was replaced, that as well did not fix the problem. since rebuild #1, the misfires are staying on one bank, 1,3,5. at some point during the part shotgunning, my mechanic, for fun, tried a troubleshooting program that involved questions, etc, and would find the problem. they gave him his money back. i should find out the name of it. but i still thought that was funny. The latest uhh.. approach is a service he has that is a remote diagnostic run out of Michigan or something that involves a step by step diagnostic walkthrough with tablets and webcams. We'll see.

anyways. sorry for the text wall. i have read i think, every misfire post on these forums. it seems the cases similar to mine, the OP disappears, trades in his jeep (only one dodge dealership here) or give up and does an LS swap. (i'm already $6500 in parts alone, not quite ready for that much more money). Ive combed the minivan forums, and them folk being less inclined to throw money at their 3.8 they gave up and blamed the engine. I'm very stubborn. and i like my jeep, even it is a stupid jerk at the moment. so. i'm wondering if:
my pcm was used, and happens the have the same issue, is there a way to check the pcm short of sending it out to get it tested?
my cats could very likely be shot due to some dummy driving a misfiring jeep for 4 days, and maybe my mechanic only did a temperature check on 2 of the 4?
and as far as a hail marys, is there any way a failing component on the serpentine system, alternator, power steering pump etc is intermittently seizing and causing enough load to mangle the timing? or would the elasticity on the belt absorb that?
i think mechanic has suspicions with the flywheel. but i can't see how it would suddenly cause issue like this.
any theories appreciated. conspiracy or otherwise. thanks.

Geordo`

so,an update. had a chat with my mechanic again today. anyone he talks to is saying he's done all the fixes they can think of, but i clarified the PCM situation. it was used from a running jeep. the dealership reprogrammed it, and ran fine till disconnected. having had a less than desirable correspondence with the dealership when they were fixing my death wobble.. i have little faith in their capabilities. so i took my old pcm home to dissect, and see if i could find anything visibly wrong with the circuit board. i'm slightly cross eyed now, and with the help of my phone camera on zoom, as well as a cheapo usb microscope, i found a blown out thingamajig. busted right in two. what does this mean? well, i think it means my pcm was the problem. so, either my dealership guys didn't program it correctly, or the donor jeep wasn't quite compatible. anyways. ordered a pre vin programmed pcm today, and once it gets here in like 3 weeks, i'll hopefully have good news. the misfire is a very rich condition, fuel pressure is running about 4psi over i guess. means misfire may have killed first rebuilt engine in less than 100km. anyways. updates hopefully soon.

Geordo`

picture of what i expect was the initial culprit.


circled in red
i'm half curious if there are any wiring diagrams for the 07 pcm, curious if the apparent should could have been cause externally, etc.

Grasschopper

That's a resistor...cost is pennies or less. Question is why is that one blown? And then what value is that? I see both 103 and 203 resistors in your photo.

What did you have to do to get to this board? i.e. can you get to a good one to see the value and if that resistor is in tact. If it's easy then you could replace this pretty easy. 10 min job to replace that part if you have the part and know what you're doing.

ronjenx

That's a three digit surface mounted device; in this case, a resistor.
The first two digits are the significant value, and the third digit is the multiplier.
For 103, that's 10 x 10 to the third power. Or, just add 3 zeros to 10. 10,000 ohms, or 10kΩ.

Geordo`

sorry i never saw the replies to the thread,
Grasschopper, i believe it was 203. there was a resister broken off entirely (likely due to my dissection of the pcm) to the left of the larger chip, running 'vertical' beside the two 'horizontal' blue and white resisters, so, i opted to get a new reman with a warranty instead of burning myself trying to solder the tiny resisters.
on that note, dissecting a pcm on these jeeps is harder than it sounds, and easy to do damage. the circuit board is well fastened to a 1/8"ish plate of aluminum that bends easily, and siliconed to the housing, prying is required, but easily bends the aluminum backing)

Moving forward, i got the raman pcm in, got it to my mechanic, and he has installed it. runs worlds better. mechanic says it still feels gutless though, and took it for a longer test drive last night. the 1-3-5 misfire may be gone, there is a couple 02 sensor codes now. and one general misfire code that immediately went away when the throttle was released. iirc correctly he checked the o2 sensor reading and they were normal, or within a normal range, but he's going to do some more in depth testing today, and check out the cats, as while the 1-3-5 misfires were happening, it was a super duper rich condition, so logically the cats could be clogged. i think. i'll keep updating as i have updates. i have a good feeling about the pcm situation, and if it's now something with the cats or o2 sensors, i will be fine with that.

Geordo`

CATS ARE BAD! is it weird i am excited about that? dropped the exhaust and ran beautifully. under load, at idle, everything. Mechanic is ordering new exhaust today, hopefully he can get it by next week before he takes 4 weeks vacation next weekend. but. most importantly i get my jeep back. i'll confirm once it's in my hands, but i guess the moral of the story is don't expect your dealership or even your mechanic to appreciate the significance of the serial number variations on these pcms? or the dealership doesn't know how to program. i'm not sure about the rules for corporate shout-outs, but the pcm re manufacturing company out of NY i went with delivered with the pre programmed unit and i can't thank them enough.

Geordo`

another update:
got old off, first cat on passenger side had disintegrated except for a baseball sized piece that was plugging off that exhaust under some loads and hills, possibly causing a general misfire code.
anyways, new cats ordered, mechanic is gone for three and a half weeks so towed it to my shop in anticipation of new cats arriving via mail. runs real nice if not f-ing loud. got the interior half cleaned just cause i felt bad about neglecting the poor thing. and installed the best top soft top 'cause i've had it for 3 years and never installed it.

Mr.T

This might be a bit too late, but I'd avoid hi-flow cats. Glad the problems are getting solved, and that you kept posting.

Geordo`

@Mr.T I don't believe they are high flow cats, magnaflow 49689...
out of curiosity, what is the reason for avoiding high flow? computer doesn't like 'em?