Here is the skinny, I purchased a 1997 Jeep Cherokee Sport from my neighbor, it kept overheating on him and he thought it was the heads. He let it go for a steal because he didn’t want to mess with it or sink any cash into it. I changed the thermostat and when that didn’t help I discovered the water pump was going bad because it was leaking coolant from the weep hole.

The only thing I had to disconnect to change the water pump was the A/C fan. Put the new water pump and the Jeep was running crappy. It ran crappy before, only after it started overheating, now it runs crappy and lacks power and wants to stall at stop signs etc. when it warms to reg. operating temp. Changed the cap and rotor put in new plugs (the cap was really bad and the plugs showed signs of too much fuel, that it was running too lean. Also ran injector cleaner through the fuel. Has anyone had this problem? Why would I have normal power etc when it had a poor water pump but now that it doesn’t overheat it runs lousy and too rich?

 

Maybe coolant temperature sensor??? I know it has effect on the idle but not sure about the A/F mixture...

 

Is it running as hot as usual? I mean up to the thermostat temperature? Had a 6.2 liter K5 once that had a piece of the spring that keeps the bottom radiator hose from collapsing break loose, go through the water pump and hand the thermostat open. It would never get up to operating temperature since the thermostat was always open.

Don't the computer controlled vehicles get more gas when they are below operating temperature? Maybe something is hanging your thermostat open - if the temperature is running below normal for your engine/vehicle.

 

Coolant temp will directly affect the A/F mix because that is what is telling the PCM whether or not to go into open or closed loop fuel trims.

 

Coolant temp has virtually no effect on a OBD-II system....the O2 sensor(s) is controlling air/fuel. I unpluged the coolant temp sensor (experiment) and the system still enters "closed loop" less than a minute after cold start-up....well below normal coolant temp.

 

Would the O2 sensor be affected by how warm or how cool the engine runs? Excatally how or what does the temp sensor do as its part of the fuel delivery? Does a cold engine cause the PCM to dump more fuel and less after it warms and when it warms the fuel delivery is not being dialed down, that is what is going on?

 

Are you sure that it doesn't have a head problem......low compression etc.

 

The O2 sensor is in the exhaust pipe and senses the amount of oxygen remaining in the exhaust and provides that lean/rich info to the ECM, so no, coolant temp has virtually no effect on air/fuel ratio, especially on OBD-II systems ('96 up).

Is your check engine light on? If so, what codes?

 

@Captainwoot,

I have not pulled a compression test on it yet because before the water pump was replaced it ran OK (for a vehicle in need of a tune up) I could still get up to freeway speed. Only overheating cause any power loss, not just getting up to reg. operating temp.

 

BS FLAG The coolant sensor has a lot to do with the way the engine runs on a 1997! Without the sensor on the thermostat neck connected the engine will run like CRAP! Ask me how I know!

 

In what way do the coolent temp. affect the operation of the fuel/air mixure or what other system? How does it tie together, so to speak?

 

Must be a big difference between a '97 and a '98 XJ, as I posted we purposely unplugged the coolant temp sensor as an experiment....ScanGauge showed the system went into "closed loop" less than a minute after cold start and it ran no different than when plugged in EXCEPT for, the efan runs constantly and the CEL comes on. URMV.

 

Just put a wp on my 2000 today. Started it up and forgot to plug the ct sensor in. Ran like crap... Plugged it in, still ran like crap.. Plugged in my buddy's code scanner and it had 5 codes....? Cleared the codes, started it up and runs fine now... I had no codes or cel before the new water pump and t stat.. Temp sensor must do something.......

 

Ran bad with or without the sensor connected, hum..........and the codes were? Changed the water pump, t-stat & housing and coolant sensor on our '98......no CEL or running issues at start-up. Only CEL was during our experiment of running the XJ with the coolant temp sensor unplugged to see how quickly it would enter closed loop. Running performance remained the same, no issues.

 

I thought it was weird to? All I know is it's fine now, no cel's at all...