Running really rough---have searched

Ok, so on Sunday I was going down I-95, when all of a sudden without warning, my Jeep lost power, like if someone shut the key off, yet it was still running. When I tried to downshift to get the rpm's up and stepped on the gas, a little bit of black smoke came out like if it had too much fuel. I had to get towed home because it would not stay running. No CEL or anything.....


...Now I finally got it to stay running, and if I slowly open the throttle body it will rev up normally, if I do it anything other than really slow and steady, it starts bogging down. at idle if I step on the gas it almost immeadiately dies like it's choking out....there was a pending code for fuel system too lean bank 1, but now it's a current code with the CEL on after messing with it on and off for 2 days. I've also noticed that the exhaust gases are pretty hot feeling, and it's also blowing out little black carbon deposits on the ground.


About my XJ-- 99 with 4.0, Manual trans

Things I have ruled out for sure:
Spark plugs, wires, cap, rotor, fuel pump, cat. converter, vacuum lines, intake gasket, CPS, cam sensor, pickup module (in distributor)

Today when looking at the live data stream, everything appeared normal, excpet one thing really caught my eye...the O2 sensor upstream was a 0.25 volts while the downstream was at 2.5 volts...the PTFT % (whatever that is) of the upstream was a negative 17.4% while the downstream was like positve 20 something percent I think, but not negative for sure.

last time I saw that was TPS thinking it was always WOT

Anybody else??? I'm pretty sure this is not a TPS issue since it rev's fine if I am really slow with it, but any kind of abrupt throttle and it cuts out altogether.....also the code I mentioned before is P0171

Also, I monitored the missfire counter with a scan tool and it's not missing on any cyl's

sounds like a bad upstream 02 sensor. when mine went bad on my 98, it lost power, surged like crazy, backfired in the manifold...would basically run like crap.

That would be the first suspect for me.

It's fixed...I too thought it was the upstream O2 sensor, but I was able to rule that out...after trying the MAP sensor with no luck, I got to thinking long and hard about exactly what it was doing and how it sounded...I decided to throw a new coil on it and BAM...run's like a champ...I reset the fuel curve memory so it has a fresh start with all new parts...drove it 13 miles from work where it has been sitting in the shop since Sunday and it runs like a champ!!!

Thanks for those of you that did reply...your advice was appreciated.

Edit: It was not the factory coil on it...the factory coil was replaced 2 years ago due to some slight hesitation issues I was having when I found a hair line crack in the coil. This was an ACCEL coil which everyone I talked to raved so much about when I bought it....NEVER AGAIN!!! Went back to OEM this time! A coil should last more than 2 years!!!

keep0njeepin0n said:

It's fixed...I too thought it was the upstream O2 sensor, but I was able to rule that out...after trying the MAP sensor with no luck, I got to thinking long and hard about exactly what it was doing and how it sounded...I decided to throw a new coil on it and BAM...run's like a champ...I reset the fuel curve memory so it has a fresh start with all new parts...drove it 13 miles from work where it has been sitting in the shop since Sunday and it runs like a champ!!!

Thanks for those of you that did reply...your advice was appreciated.

Edit: It was not the factory coil on it...the factory coil was replaced 2 years ago due to some slight hesitation issues I was having when I found a hair line crack in the coil. This was an ACCEL coil which everyone I talked to raved so much about when I bought it....NEVER AGAIN!!! Went back to OEM this time! A coil should last more than 2 years!!!

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what is this coil you speak of.. is it the pickup.. or the coil itself.. can't find it think I need the same part

.........COIL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Edit: How can you not find the coil???

High voltage spark coil.

And I don't see how the error code and symptoms fit the HV coil being bad. Something does not add up. Sounded like a bad TPS, or O2 sensor to me.

Mike...trust me, I tried everything, it's got almost all brand new sensors, including the TPS, MAP, and O2....nothing worked.

Think about it, the coil was obviously producing a weak spark, so when I would try to give it too much fuel, it couldn't keep up. Makes perfect sense to me....add's up fine!

keep0njeepin0n said:

Mike...trust me, I tried everything, it's got almost all brand new sensors, including the TPS, MAP, and O2....nothing worked.

Think about it, the coil was obviously producing a weak spark, so when I would try to give it too much fuel, it couldn't keep up. Makes perfect sense to me....add's up fine!

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I was thinking in terms of the lean error code. Too little spark would mean unburned fuel, which means rich not lean. That is the part that made no sense. But if the fuel did not burn (too little spark), the O2 also does not get used, making the O2 sensor think it is lean, as it does not look at excess fuel, only excess O2. I guess the second O2 sensor not reading lean, fits as the Cat burns the excess fuel and uses the O2 up.

Definately one of those cases where it was not "The Usual Suspects". Blame it on Kiaser Souzia.

This is one of those "once you've eliminated everything else, what's left must be the cause" kinda things.

Saudade said:

This is one of those "once you've eliminated everything else, what's left must be the cause" kinda things.

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It is also a good exercise in how to avoid jumping to conclusions. The difference in the 2, O2 sensor outputs was a good clue, if we had seriously considered it. And a weak coil use to be a typical diagnosis for old non FI vehicles, as well as a fuel problem. But as has been said, the data heavily leaned to a bad TPS for sure. If It had been mine, I would have tested the TPS with an analog ohm meter, discovered it was OK, then tested the O2 sensors (which I think he did), and then scratched my head, then tested the fuel pressure, and then really scratched my head.

keep0njeepin0n,

Congrats on debugging this one!

Ecomike said:

It is also a good exercise in how to avoid jumping to conclusions. The difference in the 2, O2 sensor outputs was a good clue, if we had seriously considered it. And a weak coil use to be a typical diagnosis for old non FI vehicles, as well as a fuel problem. But as has been said, the data heavily leaned to a bad TPS for sure. If It had been mine, I would have tested the TPS with an analog ohm meter, discovered it was OK, then tested the O2 sensors (which I think he did), and then scratched my head, then tested the fuel pressure, and then really scratched my head.

keep0njeepin0n,

Congrats on debugging this one!

Click to expand...

What if it revs fine in park and neutral, but under load.. there's no power.. TPS or something else??

Ecomike said:

It is also a good exercise in how to avoid jumping to conclusions. The difference in the 2, O2 sensor outputs was a good clue, if we had seriously considered it. And a weak coil use to be a typical diagnosis for old non FI vehicles, as well as a fuel problem. But as has been said, the data heavily leaned to a bad TPS for sure. If It had been mine, I would have tested the TPS with an analog ohm meter, discovered it was OK, then tested the O2 sensors (which I think he did), and then scratched my head, then tested the fuel pressure, and then really scratched my head.

keep0njeepin0n,

Congrats on debugging this one!

Click to expand...

Thanks! And yeah, I did just, that, tested the TPS, which I figured was good anyways cuz it's fairly new, tested fuel pressure and it was a steady 48psi even while running weird. So, only thing left in my mind was the coil knowing everything else was good!

stxcherokee said:

What if it revs fine in park and neutral, but under load.. there's no power.. TPS or something else??

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Actually, you're misunderstanding what I said....I never said anything about park or nuetral....matter of fact, it's a 5 speed anyways....what I said was if you VERY slowly opened the throttle body by hand it would rev up ok, but if you did it too quickly, like you would if you floored it, it would bog way down and run rough!

Ecomike said:

I was thinking in terms of the lean error code. Too little spark would mean unburned fuel, which means rich not lean. That is the part that made no sense. But if the fuel did not burn (too little spark), the O2 also does not get used, making the O2 sensor think it is lean, as it does not look at excess fuel, only excess O2. I guess the second O2 sensor not reading lean, fits as the Cat burns the excess fuel and uses the O2 up.

Definately one of those cases where it was not "The Usual Suspects". Blame it on Kiaser Souzia.

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Yeah I know what you mean about the code...but after some further research and using the "troubleshooting" section on my snap-on scanner, the code actually meant "Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor"


Anyways, all is well now.

I know that this sounds ridiculous, especially as you have the problem solved, but I wonder if the (bad) coil checks out of spec with an ohmmeter. That would be good information for those with coils.

No idea...I would have to say it would, since it fixed the problem, but to be honest, I don't really care at this point and it's at the bottom of the trash can at work.

stxcherokee said:

What if it revs fine in park and neutral, but under load.. there's no power.. TPS or something else??

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Hard to say, Not the TPS on 91 and newer for sure under those conditions. Also not the exhaust system. But for a Renix TPS, AW4, it can be a bad TPS for sure. The Renix TPS is two part, and if the TRanny (TCU computer) side of the TPS goes bad, and not the engine side (ECU computer) of the TPS, it can give you exactly those symptoms. So can badly dragging brakes!