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Check Engine/Temperature problems

chelms27

NAXJA Forum User
Ok, first of all I have a new temperature sensor...I changed the oil pressure sending unit and oil last weekend, and now the check engine light is on, the temperature guage stays at 110. even though it is actually warmer. Also my electric fan runs all of the time even if it is below freezing out and I have just started the jeep? Weird problems, the jeep is a 97 sport 4.0 auto. Today while I was driving it just died, upon re-start it ran sluggish all of the way home. Any suggestions would be great.

ChrisNAXJA
 
Sounds to me like you have an open in the temp sensor circuit, causing the cooling fan to run constantly...If I'm not mistaken there are two temp sensors, one single wire for the gauge, and a two pin sensor for the ECU. Make sure your temp sensor connector is plugged in all the way, also check for bent pins...
 
I just recently changed the sensor on the thermostat housing, where is the other one located? I changed the oil pressure sending unit, could it be around there and I accidently un-plugged it? If there is a sensor for the ECU, that sounds like a good place to start, thanks for the help.
 
Ok, the sensor on the stat housing is for the ecu, if it is open, you will always run in open loop, causing the ecu to add too much fuel when the engine is warmed up, which may explain your sluggish running experience. The sensor for the gauge, is a one wire sensor, near the rear of the cylinder head on the left side, close to the number six injector harness. Again, check the connection at the stat housing, pull the connector off, make sure the pins aren't bent, and that the rubber insert in the connector didn't slide down and block the female terminals. Good luck.
 
on the left sitting in the vehicle or as your looking at it? Is it in the same spot like on a renix motor in the far back of the head? If so there is no way I bumped that. I will check though.
 
double check also that the newly replaced temp sensor is the correct one for the vehicle-- it sounds like multiple problems, though as the gauge on the dash is controled by the sending unit on the rear of the cyl. head and the fan is controled by the ECU based on info from the sensor you replaced....

--Shorty
 
I replaced the temp sending unit 11 months ago, and only since changing the oil and replacing the oil pressure sending unit have I started having a problem.??
 
Check engine light still on? If so, pull some DTC's, (trouble codes) to help diagnose the problem... If you don't have an OBDII scanner available, Key ON, OFF, ON, OFF, ON...wait for check engine light to flash codes, or they may appear on your odometer...
 
97+ XJ's only have one temp sensor, you didn't happen to use any teflon tape when you put the new one in did you ? Thats part of the ground circuit, the threads need to touch steel...
 
No kidding, I think...I am 99.9% sure I did put teflon tape on the oil pressure sending unit. Could you elaborate on the ground issue you speak of? I had a 1988 and replaced the oil pressure sending unit, it came with teflon tape on the threads? Thanks RichP you might have made a simple solution to my problem.

Chris
 
Hmm....I just installed my temp sensor using pipe dope and it seems to be doing okay. Doesn't seem that the two wire plug would require a separate ground. I don't know if the pre-applied sealant on the threads of the oil pressure sending unit is a dielectric grease but that in itself does not prevent electrical contact as we know from having the underhood plugs stufffed with it, at least on the older xjs.

I don't think teflon tape will prevent metal to metal contact either but it would be simple enough to check if you have a meter -- just check for continuity ( 0 ohms) between the brass body of the sensor and the aluminum thermostat housing -- same with the oil pressure unit. I guess the first test is whether your oil pressure gauge appears to be operating properly.

Actually it doesn't make a lot of sense that your temp unit would be the culprit here after a year just as you change the oil pressure sending unit unless you did something else that might have disturbed wiring or the cooling system/thermostat. Did you have other symptoms that led to changing the oil pressure unit? I wouldn't think a faulty temp sensor would cause the motor to just die. First thing to do is read those codes as suggested by 89xjgrey.
 
Ok, I put the old oil pressure sending unit back on and now it runs fine again? Did I get a bad sensor somehow? It read the oil pressure correctly. Jeeps are weird.
 
chelms27 said:
Ok, I put the old oil pressure sending unit back on and now it runs fine again? Did I get a bad sensor somehow? It read the oil pressure correctly. Jeeps are weird.

I wonder if you got the sender for the idiot light instead of for the gauge..
 
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