Heat causing misfire in XJ

I just bought a 98 Xj and haven't had any issues with it up till Yesterday when i pulled out front of the store and the wife ran in and i sat there and just let the car idle. All was fine till it got to about 210 then it started to stumble and when it got to about 215 the check engine light came on and it started to run like crap it was spitting a sputtering and had no power at all so i ran it to autozone and they pulled the code and it came back p0305 which is misfire in cyl/injector #5. well after it cooled down it went away and ran like a champ again and had no problems the rest of the day. Well today i decided to try it again i let it idle up to 210 then it started to stumble a little and by the time it got to 215* it was apparent it was going to do what it did yesterday. So i drove around and it had a little hesitation/stumble and the CEL had not come on yet (i didnt wait long enough this time) but after driving it and bringing the temp back down it was back to normal. Whats causing this to only happen on this one injector (5) and why only when it gets up to the 210+ range?

The big question in my mind is why isn't the engine staying closer to 200.

Verify both fan clutch and e-fan operation

What is the history of routine cooling system maintenance? IE: fresh coolant, new 195 degree thermostat, new radiator cap?

It sounds like this is a "new-to-you" vehicle. Unless you have believable maintenance records from the previous owner, I would absolutely do a flush/fill, new stat and cap. For starters.

The target for most 4.0 engine is close to 200 degrees, give or take a bit either way.

Never hurts to perform a tuneup on that new vehicle as well. For a 98, that means new Champion copper plugs gapped to .035, new plug wires, premium cap and rotor (brass contact) and check air filter.

I agree, ensure the efan is working up to par, It has one speed and you should be able to hear it

I agree with Birchlake, it sounds like the coolant system needs servicing. If it overheats at 215 either it's not holding pressure or the mixture is too weak (water boils at 210*) the other stuff he mentioned (flush, stat, cap & tune up) are just preventive maintenance that you should do to any new vehicle you buy, better to know what's good than have to hope for the best.

This is a new to me vehicle but im not new to jeeps i have owned several and never had this issue. Mech fan seems to be fine electric fan is coming on checked coolant and its up and nice and green and looks real clean. I just did a tune up plugs/wires/cap and rotor and ran some seafoam In gas/oil and thru booster vac line thinking maybe the injector/s were dirty along with some other stuff then i changed the oil. So it has had pretty much everything you can think of done to it and once idling it climbs to 210 and starts to idle ruff still then when it gets to 215-217 it runs really bad and will hardly move under its own power. It hasn't thrown CEL again yet but it is still running like crap when above 210. Anything under 210 and it idles and drives like a charm. There has to be a reason why above 210 it runs ruff but im yet to figure it out:gonnablow And i cant find or seem to get a answer, im at a total loss im usually really good with cars and fixing things and finding problems but this is kicking my butt! I dont even know where else to look or what else to try.

search for "heat soak" here, that will pull up some relevant info on things to check. Lots of the later XJs have problems with it.

GrimmJeeper said:

search for "heat soak" here, that will pull up some relevant info on things to check. Lots of the later XJs have problems with it.

Click to expand...

Every heat soak threads i have read are only happening when the rig is turned off and then restarting when hot. Mine does not have that issue mine is doing it when still running and above 210* So im thinking its not a heat soak issue? i could be wrong?

crawlnfool said:

Mech fan seems to be fine electric fan is coming on checked coolant and its up and nice and green and looks real clean.

Click to expand...

Just looking at the mech fan or just giving a quick spin is not a very good test of it's condition at all. Once they get old the start to not do their job as well. A real good sign that the mech fan is shot is what is called "temp. creep" it's where when idling or in traffic the temp will just keep creeping up until it overheats, obviously right, but the problem is really the fan clutch is no longer functioning as well as it should, not the fan itself. You might want to look at that as a possible solution. Also just because the coolant is full and green it doesn't mean it wasn't just changed before you bought it or the the radiator, thermostat or heater core are not clogged and causing poor circulation of the coolant through the engine thereby causing your overheating issue. Just somethings to think about further rather than just to pass off because the "look" OK. Good luck with it.

crawlnfool said:

Mech fan seems to be fine electric fan is coming on checked coolant and its up and nice and green and looks real clean.

Click to expand...

Just looking at the fan or giving it a quick spin isn't really a very conclusive test of whether it's working or not at all. I will say that once they get old they do start to not do their job as well for sure. A real good sign that the mech fan is shot is what is called "temperature creep" it's where when idling or in traffic the temp will just keep creeping up until it does overheat, obviously right? But the problem is not the fan at all it's actually the fan clutch that is no longer locking up at low speed or high temperature (depending on the style of clutch your jeep has). You might want to look at that as a possible solution. Also just because the coolant is full and green it doesn't mean it wasn't just changed before you bought it or that the radiator, thermostat or heater core are not clogged and causing poor circulation of the coolant throughout the engine thereby causing your overheating issue. Another thing is the radiator cap, if it's not holding a sufficent amount of pressure in the system the coolant will boil over at a much lower temperature than the system is design for, maintaining proper pressurization is very important to controlling overall coolant temperature. Just some ideas of things to check a little further into, rather than just pass off because the "look" OK. Although cooling systems do seem fairly simple on the surface, it is very easy sometimes to overlook the importance of the individual pieces. That is at least until they stop working for you and you have start playing detective until you find the source of the problem, it's not fun I know but you'll find it soon enough. Good luck with it.

checked coolant and its up and nice and green and looks real clean.
=======================================================
Check belt for fit and tightness.
(I just bought a 98 Xj) Check there is no cardboard between the rad and AC condenser. Be surprised how often this trips people up
He not losing coolant so the cap is good.
It not over heating on the road so the rad has good coolant circulation.
The E fan is kicking in. But you could check it's RPM or load to check see if it's good. You can check by ear by comparing it to a known good one.
Were do you live or what's the outside temp. Up north the E fan Could handle all coolant needs all by itself this time of year. My efan has not come on for many weeks.
I would look real hard at the clutch fan and at last resort check the water pump itself. The pump vanes can be eaten up and not pump well at low RPM.

badron said:

checked coolant and its up and nice and green and looks real clean.
=======================================================
Check belt for fit and tightness.
(I just bought a 98 Xj) Check there is no cardboard between the rad and AC condenser. Be surprised how often this trips people up
He not losing coolant so the cap is good.
It not over heating on the road so the rad has good coolant circulation.
The E fan is kicking in. But you could check it's RPM or load to check see if it's good. You can check by ear by comparing it to a known good one.
Were do you live or what's the outside temp. Up north the E fan Could handle all coolant needs all by itself this time of year. My efan has not come on for many weeks.
I would look real hard at the clutch fan and at last resort check the water pump itself. The pump vanes can be eaten up and not pump well at low RPM.

Click to expand...

Outside temps are in the upper 40's so it isnt warm by any means. I just dont understand this running ruff problem i have owned 3 other cherokees and ran them in the summer at temps of 100+ outside and did a lot of wheeling in these hot outside temps and none of them ever ran like this when they reached these temps. Im not understanding why it runs ruff when only 210* and above if im cruising down the road and temps are just below 210 it runs like a champ. Stop and idle and it takes a few minutes for it to climb above 210 but when it does all hell breaks loose and i start having this problem. I can hear the elec fan kicking on and it does run at 2 different speeds so im not thinking it is a fan issue. there has to be something thats going screwy when it gets warm (210 and above) it just doesn't make any sense:banghead: Unfortunately my pockets are not deep so i dont have money to just start replacing things just to eliminate them. I have been told to switch injectors around and see if the code follows but its not always throwing a code when running ruff it did it just the one time. I guess i will let it idle up in temps again and see if i cant get the CEL to come back and see what code it throws again. If it is the same code i will try the switching injectors around and see if i can get it to throw a code?:banghead: