Jeep Wrangler JK (3.8L) Misfire Part 1

Initial problem was a P0300 (random misfire), C121C (Torque Request Denied), and a Catalyst error (don't recall exactly which one). So first things first, we have a history of damaged plug wires (because of crappy stainless headers) and I did in fact have another melted wire so I replaced the plug wire on number 4. When that didnt work, I then replaced plugs after seeing that one was bad and after failing to fire, I had an arc jumping around/through the boot and to the head. I replaced the coil pack, crankshaft sensor, camshaft sensor, map sensor, all four O2 sensors, and drilled out the top two catalytic converters. Nothing worked.
At this point I went in and spoke with my local service manager and told him that because of the C121C, I was leaning toward a PCM failure. He thought I had a blown head gasket and after a compression check I did have 50psi on number 2 cylinder (should've been ~175). Since I was planning to rebuild the motor in the winter anyway, I went ahead and tore it apart.
That's about where this video picks up. I've got the motor torn down and found that I had both seized compression rings on number two cylinder as well as a seized lower compression ring on number four cylinder.
Now it's time for reassembly to see where I'm at...

[@vardfriki7274]

Just letting you know...I read on another bid, an old timer suggested that carbon and stuck rings can sometimes be cleared by a slow stream of water through a hot engine. I had exactly the same symptoms as you. I'd priced up new NGK Iridium plugs, Mopar leads and new NGK coil pack 1000nzd.. I figured I'd give the steam clean a go first. I ran 1.5ltrs of water over 15min at 3500-400rpm after a good hot drive and then another hot drive. The difference is amazing. There were clouds of steamy soot where I did it splatters on the drive. After the run it's running the best it has in ages and the CEL is gone.

[@shawn2742]

I don't doubt that at all. Makes sense and it's good advice. In my case, I think the damage was done to the cylinders from prolonged irregular wear and I can no longer get rid of Cyl4 misfire. The plan now is an actual motor rebuild (or LS swap). But since I'm still running (pretty good actually) it's on the back burner until the 93 stepside is done.

[@theonlyoned6409]

How do you run water through your engine

[@jerrydaniel2989]

Sounds exactly like my 08 but i never had over heating problems. 5 previous owners before me and in 2021 i got it and had only right at 100k. Someone had let it set but i got it reasonably cheap from a dealer. Well. Now its just setting in my yard and definitely needed this video so compression test is coming. They sure knew what they was doin when they quit making the 4.0’s. Bahah. Never will buy another one of these junky things with these motors they are putting in em

[@ntme9]

I had a random misfire on my 3.8 jk and it ended up being the coil pack.

[@Pete-from-Tn]

Where's the link to the other guys videos?

[@shawn2742]

I'm guessing I said I'd link to something? I apologize but I have no idea, it's been a while. On another note, I'm about to tear the entire engine out to have it rebuilt so stay tuned.

[@Pete-from-Tn]

@@shawn2742 Yes you were going to link a video. That showed how the other guy did the head gasket on his. Looking forward to the new videos. Bought a 2009 JKU today with 117K perfect condition.

[@fire7340]

where's the update

[@shawn2742]

Coming soon .... as well as a full rebuild.🥺

[@reynaldosolorzano9359]

Same issue with my 08…misfire 4…need to do this compression test

[@shawn2742]

How'd it go?

[@kurtnulf3362]

By the looks of all that carbon on your top end you need to replace that PVC and install a catch can to keep some of that crap from your values and pistons

[@eyeamcreated]

They look really good not damaged 🤦 0.03 > 0.09 .. what specs run 😅🤫🤭🤔

[@MAC_6.7]

What kind of oil was it running?

[@shawn2742]

Was it running? I don't know other than him telling me that he always did full synthetic oil changes. I will say that (video for another time) he never "changed" the oil but simply put in additional oil as it leaked out. I'm not sure if I mentioned that in the video or not. I know that because the filter that was installed was very old, oily, dented, and difficult to remove. Ultimately, what that led to was a continuous cycle of running low, running hot, buildup of sludge, and then some fresh oil until the cycle repeated. I've noticed over the past 4-5 years that I've owned it that every time I do an oil change I have tappy valves. Some times thinning the oil helps but oddly sometimes a thick oil additive helps which seems counter intuitive. What I've done is cycled SeaFoam through it a few times now the week preceding an oil change. The SeaFoam breaks down the years of sludge throughout the oil passages and I've noticed improvements every time. Long story short, I don't know what oil he ran through it other than supposedly synthetic. I run SuperTech full synthetic in all my vehicles, I believe the Jeep is 5W20.

[@jorgezuni2818]

I thought you where gonna say the Dealer called . And said to stop modding the Jeep 😅..✌🏼

[@shawn2742]

Modding? Who's got time to mod when you can barely keep them running!?

[@IBtraveling]

Well how did it turn out?

[@shawn2742]

Huh ... I thought I had posted an update comment. Here's the gist of it: the real issue was caused by a clogged cat. The cat was causing backpressure and heat that was wreaking havoc on everything else. The seized rings needed to be fixed, no doubt, but I think the jeep would've kept running if not for the clogged cat issue. I still don't have it 100% because of little stupid mistakes that I keep making. Mainly, I didn't figure out the cat until a couple months after the rebuild. I bought a new y-pipe off ebay that rubs on the frame so I need to pay a shop to fix that. I've had a minor water loss problem and a nagging cylinder 4 misfire that I can't help but think is a head gasket. The Jeep is running great. Fantastic actually. Last night I just figured out the pcv valve wasn't locked in which I think was causing a vacuum leak as well as oil thru the intake that could've been contributing heavily to the codes. So to wrap this up, I want to get these nagging issues wrapped up before I post an update video but that's where I'm at.

[@IBtraveling]

@@shawn2742 okay thanks for the reply. I'm looking at buying a jeep and just trying to find possible problems of different models before I buy one.

[@austinreish94]

@@IBtraveling stay away from the 3.8 it's full of issues from factory including tipm, neutral safety switch, lack of engine power and many other issues that a dealership and Jeep will not fix without you paying out of pocket.

[@matthewsipe8905]

@@austinreish94 i just got a 3.8 jku a yr ago....no issues so far except the power does suck.... Not sure what i wanna do about it

[@austinreish94]

@@matthewsipe8905 how many miles?

[@misaelvarela9471]

Good morning I have a question I have a 07 Jeep Wrangler 3.8 V6 and I have no spark on number 3 I hooked up the Noid lights to the injectors they're fine but I have no spark I replaced the coil pack twice the only thing I come out with is hopefully it's the PCM and then I got to get it reprogrammed do you have any comments to what I'm dealing with thank you

[@shawn2742]

Oooh, that's a good one. I really don't but let me just tell you my thoughts: does the noid light work? Have you verified it on a working cylinder? Assuming it works, I'd try to figure out if you have a bad wire or pin at the input plug because I think that'd be more likely than the pcm follow that plug back behind the block to see if you can see any rubbed or burnt spots. Lastly, you wouldn't be the first person to have two bad replacement parts in a row. If those are dead ends, it's possible on a 2007 that your TIPM has issues. That was an issue on the early JKs.

[@misaelvarela9471]

@@shawn2742 thank you so much for the heads up continue being successful in what you do

[@shawn2742]

One more quick thing, I've never used a noid might but I'm assuming it's connected after the plug wire. Have you checked your wires. These 3.8's get so hot the damage wires a lot. I've probably been thru 10 sets of wires. Don't EVER try to pull a wire with a hot motor, they just separate.

[@misaelvarela9471]

@@shawn2742 Snap-on has noid lights where you could plug it in for the spark plugs and also on the injectors I have spark on 5 cylinders the injectors are all counseling well but I have no spark on number 3

[@misaelvarela9471]

Sorry about that the Noid lights are hooked up to the injectors the pulsation is fine but I have no spark a number 3 even after I install the Noid light for the plug

[@vardfriki7274]

Jeeps, lol🙃