What scanner did you use and how did you clear the codes? I feel it has to be something simple since it only showed up after the WP was replaced, which would have changed the temp at which the engine was running. Give me a 60's era muscle car, when it cran like crap you know where to look ir you could see it with your eye, no scanner needed.

 

He has a snap-on scanner. My other buddy has a cheapy like they have at autozone and advance and he clears codes for people all the time though...

 

What special method or tool do you use to clear the codes with?

 

It's a miracle. Like I posted previously, if the engine is started/running without the coolant sensor connected, a CEL/code is set and efan runs constant but didn't effect the way the engine ran.

 

Won't disconnecting the battery for several minutes clear the codes and turn off CEL? If the problem continues, a CEL re-appears and a code(s) is stored.

 

Well I'm here saying that it did affect the way mine ran. Dont know why I had all the codes pop up from just changing the WP, but they did.

 

As DJB said, you could just disco your battery for a while, and that will reset the codes. With the scanner it will ask you if you wish to erase them and just hit enter.
Autozone or advance auto will check codes for you also, but wont reset them around here anymore.. But they will let you erase them if ya ask...

 

Dude it ain't BS. I unplugged my coolant sensor in my 96 (the one on the head not the fan plug by the thermostat) and it idled like crap. Made one trip about 5 miles, shut it off. After that it wouldn't start. Plugged the coolant sensor back in and ran like a champ.
My brother had a similar issue going on in a 92 Cavalier when he broke the coolant sensor off. Put a new one in and issue went away.
I'm not sure how or why, but the coolant sensor does control idle and air/fuel mix.

 

It does richen the mixture when cold check your ETC sensor might just be a loose or dirty plug.

 

Well of course the air/fuel mixture is slightly richer when the engine is cold, the system is in "open loop" and running on an air/fuel mixture that is factory mapped/programmed, again slightly rich. Yes the coolant temp sensor tells the ECM what the coolant/engine temp is but once the heated O2 reaches operating temp (600F-650F) the system enters "closed loop" and the engine runs lean and clean based upon info the O2 sensor is sending to the ECM, well before coolant reaches normal temp,

The '98 FSM is about 3" thick and I have not read every page but no where have I read if the engine is running poorly, check the coolant temp sensor. Maybe I missed it but again, it didn't have a negative effect on our XJ performance when we purposely unplugged the sensor as an experiment.

 

I didconnected the battery all night and it did not reset anything, ran the same way the following morning.

 

So, if the system for some reason is not closing then the engine will run too rich because the O2 sensor is telling the ECM that the air/engine has not gotten warm enough to open? But if the engine warms up to were it should and then screws up, it is like more fuel being applied or air not being applied that makes the fuel mix too rich because enough air is not making it in.

 

Do u or do u not have a CEL? If u do, u need to have it scanned for any/all codes.

 

It was on prior to the replacement of the water pump. When I did the water pump I unearth the battery because I had to take out the electric cooling fan. After that the CEL did not return but where as before the vehicled idled OK and had power when the CEL was on, now that it is not on the Jeep runs crappy after it warms up. That is what I can't understand.

 

I'm going to go out on a limb here...

I don't see how changing a bad water pump for a good one will do much of anything except fix the overheating issue. He also did plugs, cap, and rotor, probably wires as well?

My guess is that you've knocked a connection loose, or maybe damaged a vacuum line somewhere, while poking around under the hood. That is where I would start, double check electrical connections and check for a vacuum leak. Should be easy enough to check both and as a bonus you won't have to start throwing large wads of cash at it until you verify the simple stuff. Also, try pulling the IAC and cleaning it. If the throttle body itself is dirty, I'd recommend removing and cleaning it thoroughly. Easy to do and may actually help.