Cylinder 6 misfire, replaced dirty plugs, 40 miles later cylinder 3 misfire

The Mando

The Mando

Member
Joined
Aug 2, 2021
Messages
49
Location
Colorado
2001 Jeep TJ that I've had almost a year that I took of my dad's hands. I haven't got around to the engine yet but I've manages to rebuild the suspension.and do the rear main seal.

So the run down, I'm in Colorado it's been cold and windy. About 3 months ago it started doing the weird whining sound that sounds almost exactly like some of those videos with the cracked intake manifold so I've almost assumed it was that for a bit. Now thinking it could be the evap line I found. The whistle happens only at stop lights and when decelerating. I can't ever get it when I'm at home. The sound was only for the first few minutes of driving when it's cold out. I hadn't heard it in awhile.

Cylinder 6 misfire, pulled the plugs and they were pretty dirty. I assumed maybe bad gas and that maybe it was just their time to be changed. Replaced plugs with Champion double platinum spark plugs correctly gapped

I had also found the middle line at the evap cannister severally cracked. Temp repair done with electrical tape. (I assumed it was good since there was no code) valve cover also found to be leaking. Need to replace the gasket and clean the wells.

Now 1 week later Im driving and everything is fine. I park and when I go to start her up I get cylinder 3 misfire, I could barely limp her home. Before when 6 misfired she drove fine like there was no issue. This time as soon as I'd hit above 3,000 rpm I'd loose all power. Pulled the plugs and visually the threads are just coated in the copper anti seize and oil from the valve cover leak. I hadn't noticed that the threaded wells were thst dirty with oil.


I'm a very experienced helicopter mechanic so this should be easy for me but I feel like I'm over thinking this. I'm going to replace the plugs with the Autolights after I replace the valve cover gasket. I'm going to then clean the wells with some carb cleaner. I'm debating on upgrading the coil rail for a cleaner spark. (Likely will leave it) I need to wrap the injectors with some type of heat wrap since I've seen that technical bulletin. I've got a new evap line coming soon from Mopar parts.

Now that may fix the misfire issue. Still my exhaust has had a rich smell for awhile since my y pipes gone back on and there's still the whistle. I'm still worried that the y pipe isn't quite on there correctly or there's a cracked exhaust manifold or intake manifold. I'm probably over thinking it since I don't quite know the system as well as I'd like.


Any feedback or input is appreciated. I know these 4.0L are basically tractor motors that soak up heat lol

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Also thinking maybe a bad cat? How sensitive is the system to throwing codes? I would figure I'd be getting something telling me what is causing the misfire such as rich condition. The exhaust smell and oil on the threads and the fouled plugs from the first change last week. This team it was only cylinder 6 that was fouled. Here's a pic of cylinder 6s plug

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just to eliminate the easy stuff I'd replace the plugs with Mopar SP000ZFR5N plugs and use 90% less anti-seize
 
Last edited:
L J said:
just to eliminate the easy stuff I'd replace the plugs with Mopar SP000ZFR5N plugs and use 90% less anti-seize
Click to expand...
I ordered the autolite. I put a pretty even thin coat on there. I'm thinking that's oil from the valve cover that's built up in there. I'm going to try and get some carb cleaner and clean the threads out tommorow without spraying to much into the combustion chamber. I need to look up the torque for the dark plugs as well just to be by the book. I went German to before and tried to coat them well enough. I just didn't want to go to tight since this engine gets hot as balls
 
Is the 4.0 that finicky? I was going for the autolites since they'll last longer and I've read they'd be fine in the TJ
 
The Mando said:
I ordered the autolite. I put a pretty even thin coat on there. I'm thinking that's oil from the valve cover that's built up in there. I'm going to try and get some carb cleaner and clean the threads out tommorow without spraying to much into the combustion chamber. I need to look up the torque for the dark plugs as well just to be by the book. I went German to before and tried to coat them well enough. I just didn't want to go to tight since this engine gets hot as balls
Click to expand...
The right Autolites are superb plugs, don't listen to those who say to return them and go only Mopar... which isn't made by Mopar anyway. Assuming you have the ignition rail without a distributor cap, two safe/good Autolite choices are the double-tipped Platinum APP-985 good for 100k miles or Iridium XP-985 good for 200k miles. Both of those use the fine-wire electrode technology that makes them fire more reliably in difficult ignition conditions. I've been running the XP-985 for probably 25 years, it's a very high quality reliable spark plug.

Make sure not to install the single-tipped platinum AP-985 which will cause a rough idle/misfires. Some spark plug guides incorrectly show that as appropriate for the newer coil-rail 4.0 engines but it's not.

The newer coil rail 4.0 is fairly finicky about what spark plugs it will run well on due to its waste-spark design. The plugs I recommended above work well in it though.
 
Ya, I ordered the XP 985s. How are are the coil rails in the TJs? I pulled mine off and it's pretty clean. I'm just suprised at how dry it is with the lack of dialiectric grease. My gut feeling is that the Evap canister wasn't holding pressure at a certain point anymore, hence the problems above 3,000 rpm. I'm guessing it was leaking just enough before to cause a rich condition and maybe the whistle but not cause a code. Who knows?! I'm going to replace it and hope that fixes the issue. I'm giving serious thought to replacing the exhaust manifold with one that isn't going to retain heat and will mate better with the existing y pipe which maybe also get replaced so the whole exhaust system. (Not for asthetics)
 
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Jerry Bransford said:
The right Autolites are superb plugs, don't listen to those who say to return them and go only Mopar... which isn't made by Mopar anyway. Assuming you have the ignition rail without a distributor cap, two safe/good Autolite choices are the double-tipped Platinum APP-985 good for 100k miles or Iridium XP-985 good for 200k miles. Both of those use the fine-wire electrode technology that makes them fire more reliably in difficult ignition conditions. I've been running the XP-985 for probably 25 years, it's a very high quality reliable spark plug.

Make sure not to install the single-tipped platinum AP-985 which will cause a rough idle/misfires. Some spark plug guides incorrectly show that as appropriate for the newer coil-rail 4.0 engines but it's not.

The newer coil rail 4.0 is fairly finicky about what spark plugs it will run well on due to its waste-spark design. The plugs I recommended above work well in it though.
Click to expand...
x2 running APP-985s no problems.
The Mando said:
Ya, I ordered the XP 985s. How are are the coil rails in the TJs? I pulled mine off and it's pretty clean. I'm just suprised at how dry it is with the lack of dialiectric grease. My gut feeling is that the Evap canister wasn't holding pressure at a certain point anymore, hence the problems above 3,000 rpm. I'm guessing it was leaking just enough before to cause a rich condition and maybe the whistle but not cause a code. Who knows?! I'm going to replace it and hope that fixes the issue. I'm giving serious thought to replacing the exhaust manifold with one that isn't going to retain heat and will mate better with the existing y pipe which maybe also get replaced so the whole exhaust system. (Not for asthetics)
Click to expand...
I had a major issue with mine about a year ago. It caused a few misfires. I thought it was my plugs (that's when I put in APP-985 at the suggestion of @Jerry Bransford ), and it wasn't, so I moved on to the coil pack. I replaced it with a standard motor products UF296. I would've gone for the MOPAR, but this was in the height of COVID, and the price was 4x that of the standard. Right now, they aren't too far off from pricing so replacing it with a MOPAR unit wouldn't be a bad thing to do if you suspect issues.
 
Gibsonfirebird12 said:
x2 running APP-985s no problems.

I had a major issue with mine about a year ago. It caused a few misfires. I thought it was my plugs (that's when I put in APP-985 at the suggestion of @Jerry Bransford ), and it wasn't, so I moved on to the coil pack. I replaced it with a standard motor products UF296. I would've gone for the MOPAR, but this was in the height of COVID, and the price was 4x that of the standard. Right now, they aren't too far off from pricing so replacing it wouldn't be a bad thing to do.
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They're not pricy at all. I mean it's a 22 year old vehicle almost. The internals look amazing. I dropped the oil pan and it looked almost brand new down there a few months back. The throttle body looks pretty dang clean as well. I figure I'll clean up what I can without having to rebuild. I just saw the MSD Ignition coil on Holleys site for $146.
 
Gibsonfirebird12 said:
Unfamiliar with MSD, but if you're going to that level of pricing you might as well get the MOPAR one. IMHO.
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I don't know, these were designed back in the day. Things have improved alot since then. I'm not a fan of the way they shielded some of their wiring and components that are very close to an extremely hot engine. I've looked at the coil pack and it doesn't feel like it's top quality. If I can find one that forms a tighter seal, will keep moisture out, produce a better spark, and keep heat from interfering with signals then I'm sold.
 
Gibsonfirebird12 said:
Looks exactly like mine, except it's red and looks cool :p
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Mine looks and feels a bit fragile. Theres 0 dioelwcyric grease on them as if it's enever even been applied. I'm just not a fan of how thin the plastic is and the shielding. It's a weird overly simplified set up I just wonder if it could be done better.
 
The Mando said:
Mine looks and feels a bit fragile. Theres 0 dioelwcyric grease on them as if it's enever even been applied. I'm just not a fan of how thin the plastic is and the shielding. It's a weird overly simplified set up I just wonder if it could be done better.
Click to expand...

I highly doubt you have a stock MOPAR coil pack then. The MOPAR one feels pretty solid. Obviously this is subjective, but I would not say it feels cheap at all. And even my standard motor one doesn't feel cheap either.
 
Gibsonfirebird12 said:
I highly doubt you have a stock MOPAR coil pack then. The MOPAR one feels pretty solid. Obviously this is subjective, but I would not say it feels cheap at all. And even my standard motor one doesn't feel cheap either.
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It's stock, my dads the OG owner. He's never replaced it. Jeeps done all the work, I've check all the records, it's never been replaced.
 
Jerry Bransford said:
The right Autolites are superb plugs, don't listen to those who say to return them and go only Mopar... which isn't made by Mopar anyway. Assuming you have the ignition rail without a distributor cap, two safe/good Autolite choices are the double-tipped Platinum APP-985 good for 100k miles or Iridium XP-985 good for 200k miles.
Click to expand...
The MOPAR plugs are made by NGK a superior Japanese manufacturer. I've run the APP-985 and the XP-985 and have come to the conclusion that they don't live up to the hype. Neither of them came close to making it 100,000 miles. Even at ~$2 each with rebates they aren't worth it. I'm following mrblaine's advice and going back to MOPAR and just change them out every 30,000 miles.
 
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L J said:
The MOPAR plugs are made by NGK a superior Japanese manufacturer. I've run the APP-985 and the XP-985 and have come to the conclusion that they don't live up to the hype. Neither of them came close to making it 100,000 miles. Even at ~$2 each with rebates they aren't worth it. I'm following mrblaine's advice and going back to MOPAR and just change them out every 30,000 miles.
Click to expand...
We'll just have to agree to disagree on your claims about Autolite. Certainly there are lots of people here happily running them. If they were as bad as you claim they wouldn't still be in business nor would any of us here be happily running them.
 
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L J said:
The MOPAR plugs are made by NGK a superior Japanese manufacturer. I've run the APP-985 and the XP-985 and have come to the conclusion that they don't live up to the hype. Neither of them came close to making it 100,000 miles. Even at ~$2 each with rebates they aren't worth it. I'm following mrblaine's advice and going back to MOPAR and just change them out every 30,000 miles.
Click to expand...
NGK is a top notch brand. It's the material and the build spec that I'm interested in. Both seem to hold up. I just don't want to be changing them right away or worrying about premature failure.
 
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