Cylinder 3 Misfire & Upstream O2s (cats heat soak or PCM - P0303, P0032, P0058)

rasband

rasband

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While dialing in issues that weren't throwing codes (loose PCM connectors, this has been dealt with) I now have a new set to chase while dialing in this LJ (4.0L, 6spd).

I replaced the spark plugs (Autolite XP-985, gapped to 0.035) and all O2 sensors (NTK) last fall.

This week I did notice some power loss a few times, one of which definitely seemed to be due to heat soak - even though it's an 06 with the manifold shielding (I have the injector insulators on the way).

What other things can be involved? Is heat soak and a misfire likely to trigger the O2 sensor codes? Would it instead be the cats?

What's the best way to dial in on which it is? Should I add the insulators (arriving thursday), reset the codes, and drive a bit?
 
The heat soak issue related to the FSB will only cause misfiring issues on startup. The injectors will cool off after having some gas put through them and the Jeep is back to normal. I dealt with that issue for years before getting heat shielding. I had an unrelated starting issue and ordered new injectors. Funnily enough, brand new injectors were worse in terms of heat soak than my 230k mile ones. I ordered some from Davey's and they've been much better.

If you are having a really bad misfire on hot startup (IE the Jeep shakes badly), that is heat soak. But it should go away shortly. It wouldn't cause the issues you've been having with the Jeep shutting off suddenly.
 
I did the heat shielding and injector shielding kit recently. Still getting heat soak p030X codes and now a p0431 code. Ordered cats hoping that resolves it. Power seems to drop off above 3k. I have 82k on the Jeep so it makes sense. Will see if it works. Hot cats could be driving the heat soak. Temps stay around 215 driving or idling with AC on.
 
jodomcfrodo said:
The heat soak issue related to the FSB will only cause misfiring issues on startup. The injectors will cool off after having some gas put through them and the Jeep is back to normal. I dealt with that issue for years before getting heat shielding. I had an unrelated starting issue and order new injectors. Funnily enough, brand new injectors were worse in terms of heat soak than my 230k mile ones. I ordered some from Davey's and they've been much better.

If you are having a really bad misfire on hot startup (IE the Jeep shakes badly), that is heat soak. But it should go away shortly. It wouldn't cause the issues you've been having with the Jeep shutting off suddenly.
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I think the stalling issues are unrelated to this, those seem to have been from the PCM connectors being loose (e.g. the connectors would lose connection entirely and the PCM couldn't fire the coil). That issue seems to have been fixed.

I haven't even noticed misfires yet, so the code surprises me. The sound when I experience the loss of power is a louder sound that seems to be like a clogging of the exhaust - but I don't really know. It was after a sit on a hot day (90+) recently and on my way home - but not right after startup. So seems like it may not be heatsoak (for <$15 I will still install the shields).
 
AMS417 said:
I did the heat shielding and injector shielding kit recently. Still getting heat soak p030X codes and now a p0431 code. Ordered cats hoping that resolves it. Power seems to drop off above 3k. I have 82k on the Jeep so it makes sense. Will see if it works. Hot cats could be driving the heat soak. Temps stay around 215 driving or idling with AC on.
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My temps seem to be what I expect, also running AC sometimes. Did you do anything specific to diagnose the cats? I'm at 62k miles.
 
Just intuition based on the codes and symptoms. I’ll look them over when I pull them off. I reset the PCM several times and the p0431 comes back every drive cycle. The p030x only come back when I hot start and it idles rough. No other codes. I tend to over maintain stuff too. I don’t wait until it’s completely broken to fix it.
 
rasband said:
I think the stalling issues are unrelated to this, those seem to have been from the PCM connectors being loose (e.g. the connectors would lose connection entirely and the PCM couldn't fire the coil). That issue seems to have been fixed.

I haven't even noticed misfires yet, so the code surprises me. The sound when I experience the loss of power is a louder sound that seems to be like a clogging of the exhaust - but I don't really know. It was after a sit on a hot day (90+) recently and on my way home - but not right after startup. So seems like it may not be heatsoak (for <$15 I will still install the shields).
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The common issue with heat soak in TJ's is on startup. The shielding is worth it for $15, but it doesn't sound like you are having that problem. I've had random misfire codes before on my Jeep (that sudden flashing CEL was unnerving in the middle of Hells Revenge), but they always seem to just fix themselves. Sounds like you may have something more going on though.

For what its worth, my Jeep had a bank 2 code on for over ten years. We didn't feel like paying to fix the cats and just went to inspection when the light turned itself off. Eventually they had to get replaced to get an inspection done.

Could just take the cat off, jam a stick through it, and reinstall it if you want to be a redneck about it. The upper cats are a little more difficult though :LOL:
 
I did the Eastern brand off Amazon for $266-ish. Bad reviews on the Flowmaster on Amazon being a knock off and showing up without mandrel bends. Didn’t check Summit, but looks like a deal for sure.
rasband said:
I found a good deal on the cats, sub $300 and it should pass Colorado emissions.

https://www.summitracing.com/parts/FLO-2049170
I’d rather spend the lower amounts and work up than start big (PCM).
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AMS417 said:
I did the Eastern brand off Amazon for $266-ish. Bad reviews on the Flowmaster on Amazon being a knock off and showing up without mandrel bends. Didn’t check Summit, but looks like a deal for sure.
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This is definitely a case where I don’t know enough, I read a small amount about mandrel bends but not enough to justify double the cost. There were a few ratings that mentioned this, but many more that did not seem to care.
 
There is a small exhaust shop off Colfax and Havana; Castillos mufffler. Their costs are really reasonable if you want to try them. Small family run shop. I had them bend my exhaust for $40 to clear the shocks when I did my tummy tuck. Not sure what they would charge for checking cats, or what brands they would offer for a replacement. Thought I would throw that out there for you to think about (if you dont want to handle the exhaust yourself).
 
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This evolved since the codes first appeared into the PCM kiss of death, so hopefully the WranglerFix is all I need and I can return the CATs to recover a little of the outlay.
 
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