Jeep TJ Running Rough Before & After Repairs

[Auae85]

My younger son is in the Army out of state. He has a 2005 Jeep Wrangler with 4.0L and 6-speed. He has about 106K miles on it, and just experienced catalytic converters failing / getting clogged, which caused it to run rough / poorly. The rear one right off the engine was glowing orange. The whole time, no CEL on the instrument panel. Anyway, my son replaced the plugs and a muffler shop replaced the exhaust from engine to muffler outlet with parts my son supplied.

He called me on the way back to the base and said it is still running like crap. He has over 3/4 tank of gas; I suggested some condensation since they have had some recent cooler temps, but he insists its running like it was before the exhaust replacement. Still no CEL.

Any thoughts? I hate that he is too far away for me to drive over and help.

 

[Needleman]

I would still check for codes at an AZ or Advance. Sounds like too much fuel -- maybe injectors -- is his mileage down? Did you get a chance to check how the plugs looked? How many cats does it have? There may be more than one plugged or bad. Maybe an O2 sensor as well, but that should trip a CEL.

 

[zvm77us]

tell him to buy an elm327 bluetooth, download torque pro and torque scan , afterwards let him compare the readings between the oxygen sensors

 

[eljefino]

Does the CEL work during key on test? Sounds like it should definitely be on. Maybe someone tampered with it before he bought it.

 

[Auae85]

CEL works on startup. He bought the Jeep last February, at 95K miles, and it's been relatively trouble-free until now. I have a 2005 Wrangler LJ I bought new, so I'm familiar with Jeep quirks for the most part and am trying to help him via telephone. He showed me the old plugs via Facetime, and they looked normal colorwise, but #6 had opened its gap almost double the spec. It was the cat serving cylinders 4-6 that was glowing orange, so I don't know if tht was a contributor to its demise.

He is checking to be sure no new plugs are cracked and that the coils are seated properly. Also pricing new injectors.

 

[Mitch]

Key on -off three times, the odometer will display the trouble codes if present

 

[Chris142]

Its very easy to get a plug boot off when reinstalling the coil rail. You do not need a code reader to read the codes on that jeep. Get in,shut the door and turn the key on,off,on,off then on and any codes will show on the cluster.

 

[Chris142]

Oh one more thing. These jeeps are very picky about plugs. Do not put any single platinum plugs in it. It will run terrible.

 

[Auae85]

My son sent me a pic of the old plugs, bottom to top, cylinders 1 to 6. Also sent a video clip that sounded like maybe one cylinder isn't firing. Maybe a coil issue? He just installed Autolite APP985 double platinum plugs.

 

[JLTD]

I had a couple of 4.0s, and they did not like fancy plugs; stuck with original Champion or NGK and they were good to go.

O2 sensors fail rich so definitely agree to check codes.

Coils for the single miss is possible... check the whole coil unit, have him pull off wires and see if there is corrosion anywhere.

 

[Gasbuggy]

Wonder if he burned a valve.

 

[DdDd]

Check engine doesn't mean much. You have codes... They're just not bad enough to display yet. View them by cycling key on off three times or use code scanner. The ecu is pretty good about telling u what to do next.

90 percent certain it's a throttle position sensor. They go bad you don't get code and they're in a spot that gets abuse. Happened to me twice. The car runs terrible. Oxy sensor doesn't run as bad. Easy fix two screws and youre done.

 

[kc8adu]

that #6 may be an original from the look of it.
is it hard to get to?
a plug that has way too large a gap can cause a coil to fail.
the voltage overshoots and the coil can suffer insulation breakdown.

 

[Chris142]

The cats were likely destroyed by those worn out plugs. If they were OE they went almost 4x the recommended milage.

I have never seen a 4.0 with a bad valve or injector. Not saying it can't happen but it is very rare. I have seen a bad coil rail or 2. Likely caused by worn out plugs. Its definatly due for o2 sensors with 106k on it.

 

[kc8adu]

agreed.
cracked head,broken piston skirts,yes.
the only trashed 4.0 i saw was run out of oil and coolant.
it was driven over 100mi with every light and warning on the dash going off.
it didnt lock till it was shut down.
owner was still asking why it could not even be rebuilt.
idiot!

 

[Auae85]

My son called last night after sending the video clip to his cousin, an ASE-certified mechanic. Cousin (my nephew) thinks it might be IAC valve, because my son says it idles smooth for several seconds, then starts runing rough, then smooth, rough, and so on. I told him to check for codes the way you guys suggested, and I thought about the TPS too. He'll check later today and get back with me.

Yep, the 4.0L is a good engine. I have 143K on my 2005 4.0L LJ and had the cats crap out at 119K. Otherwise, it has been realtively trouble free. I once had a 1990 Cherokee Laredo 4x4 with a 4.0L that liked to eat its TPS about every 30K miles. I bought it with 130K and sold it with 230K. Only major mechanical issue with it was a water pump failure.

 

[WyrTwister]

All I can say is the cat glowing orange sounds like a very rich air / fuel mixture , for what ever reason .

Just for grins , check for loose / off vacuum lines and electrical wires .

Sorry , I know little / nothing about Jeeps .

Best of luck to you and your son . Please thank him , for us , for his service to our country .

 

[Auae85]

Thanks, my son is proud to serve, as I did years ago. Sort of a family thing, for multiple generations.

He called and said he did the ignition switch procedure. Odometer said "done" on third ON position of key. CEL blinked 10 times and stayed solid. He even repeated it via Facetime so I could see it. Apparently no codes are stored. Son also said he removed and cleaned IAC, and Jeep appeared to idle better, but the rear cat started heating up again. Crap. Looks like dealership time, by way of tow truck, so he doesn't burn out / melt down another cat.

 

[dishdude]

Vehicle has every symptom of misfire other than a blinking check engine light. A good tech should be able to figure this out pretty quickly.

 

[Auae85]

Man, I hope so. I have been the mechanic of the family for a while, mainly because I am thrifty or poor, depending on circumstances. I have taught my son some things, but like me, he will need to learn on his own as well. Unfortunately he is 3 states away, or I would try to help more. A few other internet searches seem to focus on upstream O2 sensor being a prime suspect. The failure of the CEL to log it as such is equally as frustrating. I checked my own 2005 LJ, and just like his, my CEL blinked 10 times.