Check Engine Light
Thread Starter
Senior Member
Joined: Jan 2010
Posts: 536
Likes: 0
From: Lyons, Oregon
Year: 1991
Model: Cherokee
Engine: 4.0 HO
Check Engine Light
Ok before i get yelled at, I did search for this but didn't find anything specific. My check engine light came on today, didn't notice any difference in running, went away next time I started it. We had a high of -16 yesterday with almost 3 feet of snow, don't know if that had anything to do with it. I tried the key on, off, on, off, on thing with no results. Thanks in advance! Coach
Thread Starter
Senior Member
Joined: Jan 2010
Posts: 536
Likes: 0
From: Lyons, Oregon
Year: 1991
Model: Cherokee
Engine: 4.0 HO
Ok, check engine light is coming on more frequently, engine is running rough, loss of power then goes back to normal. Shut it off and restart and the check engine light goes off. I tried the on off on for 3 cycles, 5 cycles and 7 cycles with nothing happening, no flashing nothing. This is a '91, don't know if that really means anything. Any suggestions???
CF Veteran
Joined: May 2009
Posts: 10,436
Likes: 72
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
Put your key in, turn it to the first position This should be "unlock" but no lights coming on. When you do the on/off you go back to unlock, not totally off.
I usually do about 5 cycles. On, "off", on, "off", on, "off", on, Off, On.
Then you sit there, all the lights will do their cycle, and then the CEL will start flashing.
I can do a video later/tomorrow showing the key if you want.
I usually do about 5 cycles. On, "off", on, "off", on, "off", on, Off, On.
Then you sit there, all the lights will do their cycle, and then the CEL will start flashing.
I can do a video later/tomorrow showing the key if you want.
Trending Topics
CF Veteran
Joined: Sep 2010
Posts: 21,168
Likes: 5
From: Milwaukee, WI
Year: 1987
Engine: Check
No, this does not sound like a bad head gasket. Especially if the CEL is on and off, and the rough running condition is intermittent.
Get the codes pulled, if you can't, get a friend to help. Then go from there.
Thread Starter
Senior Member
Joined: Jan 2010
Posts: 536
Likes: 0
From: Lyons, Oregon
Year: 1991
Model: Cherokee
Engine: 4.0 HO
I read the owners manual and it says it's an emissions system thing, so I'm guessing my O2 sensor is failing. The light is coming on everytime I start it now, it'll run rough for a few minutes then smooth out. I've pulled codes from a dodge I had using the key on/off method, this just does not want to do it. I'm going to call the local guy and see what he'll charge me to pull the codes. Thanks. Coach
CF Veteran
Joined: May 2009
Posts: 1,844
Likes: 4
From: Glen Burnie, MD
Year: 1994
Model: Cherokee
Engine: 4.0 H.O. K&N, Borla headers, custom down pipe, magnaflow hi-flo cat, flowmaster to turn down tip
check your fuel injector connections to the plug. mine did the same thing, when i moved to Washington state from Cali i noticed i a few times, sudden loss of power especially on the freeway, and all it was that i had a bad connection with my #1 fuel injector. i put connector grease on all of them and the problem went away. so just make sure all of your sensors have a good connection and everything else with a plug, and yes this seems to be a common problem in cold (below freezing) weather.
CF Veteran
Joined: May 2009
Posts: 10,436
Likes: 72
Year: 2000
Model: Cherokee (XJ)
Engine: 4.0
The Quick Paper Clip Test
Since we are looking at the connector pins, it should be mentioned here that a quick method to see which trouble code or codes are being set in your cars ECM is to jumper the A and B pins of the 12 pin ALDL OBD1 connector with a paper clip. While the car is off, sitting still, turn the ignition key forward while this jumper is in place. Do not start the car. The Service Engine Soon ( SES ) light will flash in a repeating sequence, telling which trouble codes have been set in the ECM. A service manual for your year car will have a chart outlining what each trouble code stands for, or this Trouble Code website can be of help. This paper clip method will tell you the trouble code or codes set in your ECM, but it will not tell you what conditions the trouble code is being set under, or let you clear the trouble codes on the fly, as the ALDL cable and PC setup will.
Since we are looking at the connector pins, it should be mentioned here that a quick method to see which trouble code or codes are being set in your cars ECM is to jumper the A and B pins of the 12 pin ALDL OBD1 connector with a paper clip. While the car is off, sitting still, turn the ignition key forward while this jumper is in place. Do not start the car. The Service Engine Soon ( SES ) light will flash in a repeating sequence, telling which trouble codes have been set in the ECM. A service manual for your year car will have a chart outlining what each trouble code stands for, or this Trouble Code website can be of help. This paper clip method will tell you the trouble code or codes set in your ECM, but it will not tell you what conditions the trouble code is being set under, or let you clear the trouble codes on the fly, as the ALDL cable and PC setup will.
Thread Starter
Senior Member
Joined: Jan 2010
Posts: 536
Likes: 0
From: Lyons, Oregon
Year: 1991
Model: Cherokee
Engine: 4.0 HO
nope the jeep is running rough with noticible lack of power when first started, after a few moments (not necessarily minutes) it'll clear up and return to normal. Tried the on/off/on thing again, no flashes and I couldn't find the plug pictured above, whereabouts should I look for this dang thing?? Thanks for all the help! Coach
