Stumble at 1800 RPM: O2 sensors?

[adventureboss]

So I noticed today a slight stumble between 1800-2200 rpm when I'm accelerating somewhat hard. Like a tiny jerk back and forth. I have an 06 with the 4.0 and the six speed manual. No codes or anything. It's barely noticeable but I can tell. It doesn't happen anywhere else in the rev range, so I'm guessing that would rule out fuel injectors/ fuel pump. Plus the fuel pump was replaced somewhat recently. I also replaced the TPS with a Mopar unit about 30,000 miles ago too. Spark plugs are the original copper NGKs and have about 22k miles on them. The confusing part to me is that it happens only occasionally. It usually accelerates just fine.

So I'm thinking it makes the most sense that it is likely an O2 sensor. Thing is, I replaced those almost a year ago. Could they already be bad? Granted I've driven the Jeep about 40k miles since. These are the NTK/NGK ones that everyone recommends too. I changed out all four. So are they already going bad? Or should I look at something else?

 

[TheBoogieman]

I'd replace those old copper plugs with Autolite XP-985 iridium ones, even if that isn't the issue. Copper plugs don't last long. Mine were shot at 20,000 miles.

 

[macleanflood]

Original PCM?

-Mac

 

[adventureboss]

I'd replace those old copper plugs with Autolite XP-985 iridium ones, even if that isn't the issue. Copper plugs don't last long. Mine were shot at 20,000 miles.

Yeah, I think I possibly messed up using copper plugs. The idea was that I could check compression, etc. whenever I had to change out the plugs but if this is the issue, it's going to be annoying changing them out every 20k and won't be worth it.

 

[adventureboss]

Original PCM?

-Mac

No, I replaced the PCM with a WranglerFix at about 154k miles. I've got 172k now.

 

[adventureboss]

I still have the Crown camshaft position sensor lying around from when I replaced the OPDA. The one in my Jeep right now is the Mopar original sensor. I might just throw the Crown sensor in to see if it helps things.

 

[Tob]

Does it usually happen after a cold start?

 

[adventureboss]

Does it usually happen after a cold start?

Actually after its warmed up

 

[adventureboss]

Swapped out the camshaft position sensor with the Crown one. I think it idles a little smoother but might be placebo. Still stumbles a little though so not the issue unfortunately.

 

[tr21triton]

sounds like the way mine started acting right before my cat shit the bed !

 

[adventureboss]

sounds like the way mine started acting right before my cat shit the bed !

I sure hope its not my cat. I replaced it a little over 20k miles ago.

 

[macleanflood]

New parts are all shit. Doesn't take much to test it out with an IR thermometer.

-Mac

 

[HammeredSole]

I just did a complete overhaul, reloom, and many sensor replacement on the 4.0. It was a chore tracking down OEM for most parts, and went NTK on O2 sensors. It didn't need them, but I've heard they're out of production. If things start going downhill, it's getting swapped.

 

[adventureboss]

Ok so it does it at wide open throttle too. Per my understanding, wide open throttle puts the PCM in open loop mode and disregards any input from the oxygen sensors right? So that rules out O2 sensors? I'm leaning towards spark plugs now because they are the conventional copper ones but would bad spark plugs cause an intermittent stumble? I thought it would be more consistent and happen every time under hard acceleration at low rpms.

 

[HammeredSole]

Ok so it does it at wide open throttle too. Per my understanding, wide open throttle puts the PCM in open loop mode and disregards any input from the oxygen sensors right? So that rules out O2 sensors? I'm leaning towards spark plugs now because they are the conventional copper ones but would bad spark plugs cause an intermittent stumble? I thought it would be more consistent and happen every time under hard acceleration at low rpms.

You should probably just try new plugs before you do anything else. I bought my 04 with a code for cylinder 2 misfire. The previous owner seemed baffled by it. The plugs were a complete mixture of brands and age, with cyl 2 being the worst of all of those. Pulling your plugs will begin to tell the story, it's just annoying getting the rail off. Remember cylinder 1/2, 3/4, and 5/6 share coils.

 

[adventureboss]

You should probably just try new plugs before you do anything else. I bought my 04 with a code for cylinder 2 misfire. The previous owner seemed baffled by it. The plugs were a complete mixture of brands and age, with cyl 2 being the worst of all of those. Pulling your plugs will begin to tell the story, it's just annoying getting the rail off. Remember cylinder 1/2, 3/4, and 5/6 share coils.

You were right! Replaced the plugs with the Autolite XP985 iridium ones and all is good. I feel silly, just surprised that the copper plugs were already bad at 20k miles.