I found this other codes chart and it says 21 is the O2 sensor. http://www.go.jeep-xj.info/HowtoECUcodes.htm How many O2 sensors are on the '91's? I'll probably replace the O2 sensor and TPS and fuel pressure regulator (fuel pump never shuts off) at the same time. Coach

 

1, maybe 2.

Im thinking just the one on the downpipe though.
If theres 2, the other one is in the cat.

 

coach were you able to fix the problem? mine is doing the same. the cold it is the longer it takes to before hesitation goes away.

 

Mine did the same thing... the stock exhaust manifold cracks very frequently (mine did on both of mine) and causes that o2 to go off sometimes (i dont know why only sometimes... but its deffinitly on and off).. when its going off mine stuttered and hurt my milage pretty bad... Get some headers and check the rest of your exhaust.. fixed mine!

 

I put a new O2 sensor in, running pretty good now!! Got it from Rockauto, great price. Coach

 

Hi Coach,

I'm having a similar issue, I randomly got a check engine light for a few hours; codes P0136 and P0130, which point to O2 sensors. My fuel economy on the last tank was only about 12.5 mpg, have you noticed your mpg increase since the switch?

 

I don't really track my mileage so I didn't really notice anything. I just drive it and put gas in it. Coach

 

1) Start engine
2) Rev to 2500 rpm
3) allow to return to idle
4) Cycle a/c
5) shift thru all gears with foot on brake (stopping and allowing each to engage
6) shut off, turn on (without starting), shut off, turn on (without starting), shut off, turn on (without starting)
7) Check engine light will stay on
8) After a few second check engine will flash codes

If you follow this and still don't get at least a 55 code, I would say computer is not working properly. this process is for 91-97.

 

I finally got the check engine light to flash by turning ac on and off after the key on/off 3 cycles. O2 sensor was the culprit, replaced, running good so far.

 

Coach,

when you are sitting in the driver seat, look right above your right knee the ADL is mounted on the lower dash panel.

also, change the fuel filter. I have a 91 also, an they is notorious for fuel bucking with a clogged filter etc.


hope it helps!

cpnwrench

 

Thanks for the reply, I looked for the ADL, it's not there. Can you take a pic of it so I can see if it's one of the plugs hanging under the dash? My fuel filter has about 10k on it, I guess it wouldn't hurt to change it out, they're not that expensive. Coach

 

I will post pic here tonight when i get done work.....

sounds like you got it fixed though!!!! O2 sensors make weird crap happen.


cpnwrench

 

i was able to fix my hesitation by cleaning the throttle plate. it was slightly gummed up. i guess when it was cold it was holding the plate slightly open. i had to clean it a couple times but have not had a problem since then.
mike