Chasing down a misfire - coolant temp sensor?

Lone Star XJ · 05-20-2009, 04:37 PM

I am trying to chase down a misfire in cylinder one. I have replaced the plugs (Champions), wires, cap and rotor. The injectors have been cleaned, ran Techron through two tanks of gas, cleaned TB, IAC, used Mopar engine decarb, etc. I still need to swap the injector from cyl. 1 with another to see if the misfire follows and do a fuel pressure check.

Could the engine coolant temperature sensor cause a misfire? I ask because my idle is always at 750rpm regardless of outside temperature. Granted it doesn't get too cold here, but it has been in the 50's the last couple of nights. My truck has been harder to start, idling rougher than normal and throwing the misfire code instantly. My coolant temp gauge on the dash jumps up to 210 really fast. I have never had a truck show that the engine was up to operating temp so fast.

98jeepxjlimited · 05-20-2009, 05:05 PM

well if your temp goes up really quick ...you might need a cooling system flush. and maybe a new radiator. for future ref. operating temp for an xj is 195. so 210 is kind of hot, so you might need a new thermostat too, possibly water pump if its real old ...wow you really went through everything that i would have thought of for a misfire and then some. if it were me, id problably do a compression test next to see if the rings r toast. and testing to see if the exhaust and intake valves are good is a good idea as well. maybe you can get new fuel injectors before you do a compression test, i dont trust any of those BS fuel cleaners or anything like that.

Lone Star XJ · 05-20-2009, 05:57 PM

I forgot to add. Compression on cyl. 1 is 150psi. The others are 160 to 170. I will check out the thermostat, etc.

**CJ7-Tim** · 05-20-2009, 08:10 PM

Quote:

Originally Posted by Lone Star XJ

.. I still need to swap the injector from cyl. 1 with another to see if the misfire follows and do a fuel pressure check...

Before you spend any money on new parts, you need to swap the injector and see if the misfire code stays on the #1 cylinder or follows the injector.

210* is the normal operating temp indicated on the instrument panel gauge.

98jeepxjlimited · 05-20-2009, 08:19 PM

i thought xjs were supposed to run at approx 195 give or take a couple degrees??

**xjfever** · 05-20-2009, 08:23 PM

They use a 195* thermostat, but operate at or around 210*

98jeepxjlimited · 05-20-2009, 08:33 PM

i have a 180 thermo. and it operates at 180 . constantly

Lone Star XJ · 05-21-2009, 07:37 AM

Quote:

Originally Posted by CJ7-Tim

Before you spend any money new parts, you need to swap the injector and see if the misfire code stays on the #1 cylinder or follows the injector.

210* is the normal operating temp indicated on the instrument panel gauge.

Will do. Picked up some new orings incase I mess one up pulling the injectors out.

Lone Star XJ · 05-21-2009, 05:51 PM

I just swaped the #1 and #2 fuel injectors and it made no difference. I can pull the plug to the #1 injector and you can barely hear a difference in the way the engine runs. It makes a big difference if you pull the plugs to angy of the other injectors. I guess fuel pressure is next.