MS Fowler

1999 4.0 liter auto
A few weeks ago I got a check engine light. The codes were PO 132/ 135 and 138. When I investigated, the bank 1, sensor 2 ( after the Cat) the wires were torn. Evidently, the piece that holds the wire harness had failed which allowed the wires to stray and the front U joint on the drive shaft grabbed them.
I replaced the O2 sensor and cleared the codes.
After some extended idling, the idle became rough and surging, andthe CEO came on, and the same codes were stored.
I cleared the codes, and it ran fine, until I had another period of extended ( over 5 minutes) then the idle surged and the light came back on, same codes.

After about 5 of these cycles over a week, I replaced the O2 sensor with one from my stock of take-off parts. I cleared the codes.
Again, after some extended idling, the CEO, and rough idling returned.
Same codes.

I replaced the throttle body and its sensors with another one of my take-offs. No change--exactly the same symptoms--after extended idling, the CEO lights up and the idle gets rough.
I all this time the mid speed and high speed performance is fine; no affect.

So I guess I need to troubleshoot the voltage coming to the O2 heaters. How do I do this?
What else do I need to do?
Thanks for your help?

Gee oh Dee

Moved to OEM tech.

Spoonman

Have you checked the codes that keep causing the cel to come on each time or did you just clear the codes and keep running the jeep after your initial set of codes came up?

VTJeep

literally- same issue in my jeep.. its a bucking chugging kinda thing and it pops (like a backfire) from the manifold...for a long time it wouldnt throw a code, so i replaced the plugs/wires, cap/rotor, IAC, TPS, checked the pump, blew out all the gas lines, sea foamed everything... all of this added up to a slight improvement, but the issue still remained. so then the o2's got replaced (got the good 4-wire, heated ones) and it bucked once, then ran like a dream. went from 11mpg to 19!! but now its pretty much back to where it was.
the odd thing is that if i floor it for a sec. when i take off, the hesitation thing goes away. it will still chase idle, though. not always, but often when its running i can be driving, in N or in P and blip the throttle it will jump and hold RPMs for like 2-3 sec. so IDK WTF to do, but i figured id share my experience cause it sounds like exact same thing... i was recently referred to the site cherokeetech.com good people, good advise. use your same name from here if you do decide to sign up. just make sure to tell em VTJeep sent ya! good luck.

VTJeep

i also went away for a week during thanksgiving and pulled the battery out for that time. got home, reinstalled it and it ran problem free for like 2, maybe 3 months... just another thought...

MS Fowler

First of all, I apologize for posting in the wrong forum.
Secondly, every time the CEL came on, I retrieved the codes, and then cleared them. Maybe I don't know what you mean by "checking the codes".
I have a digital VOM, I can read the voltages for the heater circuit, but I need to know what voltages I should see.

Spoonman

I only asked to be sure that you checked and actually were getting the same code each time the engine light came on rather that to assume it was the same after your initial reading.

kenjen11

Check the fuses for the O2 sensors. If they are good look for bad wiring to the O2 sensors.

MS Fowler

Thanks for that lead. I didn't have a fuse diagram, but in the under-hood fuse box on the passenger side, I found a blown 15 Amp fuse. Since I replaced it, I have not had any problems--its only been 30+ miles, but maybe 20 minutes of idling, and SO FAR the problem had not recurred.
YEAH!!!!!