Engine/Transmission (1998.5 - 2002) erratic temp gauge-runs rough

[Daddy]

I need some help guys. This problem has just developed, it happened about 3 weeks ago one time and cleared up and now its back. When the truck is cold it is running really rough and the temp gauge fluctuates all over the place. It seems to clear up once completely warmed up and the gauge stabilizes and it runs fine. Also sets check engine. I unhooked the batteries to clear codes and replaced the coolant temp sensor. Still have problem. Please help, truck is still under warranty but I would rather have all my teeth pulled than take it to the dealer. They seem terrible at troubleshooting. Thanks

 

[rkressg]

Colant temp. problems

Daddy,

I tried to send you a PM, but my computer is acting like it has Microsoft products installed on it. So I will place it here.



This is long winded, but I hope it helps.



What codes are you getting, turn the ignition on, off, on, off, on without starting and look at the odometer, it will show you the basic p codes from the ecu and pcu.



There were two problems with my temp gage. First off, my thermostat was not completely opening, causing the engine to run warm (220) while towing. I bought a new thermostat from Cummins. This aided the problem some. A few months after that, the gage in the dash went nuts. The temperature sending unit would cause an engine over-heat code, temp sensor over voltage, temp sensor undervoltage. They were codes p0117, p0217, and p0218 I think. I would have to check on that.



More importantly, the remedy. The wire harnes end that connects to the colant temperature sensor on the front of the motor went bad. the wires inside the connector were shorting out (don't ask how). The fix was to replace the end, the part that clips onto the colant temperature sensor. It is a plastic connector with a purple seal ring on the inside. The part is just to the left of where the upper rad hose comes out of the block, next to the thermostat housing.



If you think your colant temp sensor is bad, get a good multi-meter and check the resistance (I can't find an omega symbol) across the two leads. Put the sensor in a pot of water and heat. The resistance between the two leads should drop the hotter the water gets. I can get you the specs on ohms if you need them.



All and all, to fix this, I replaced the collant temperature sensor, wiring harnes connector to the sensor, the thermostat, and I fixed a coolant leak that I had from an improperly set freeze plug on the back of my head (thanks to a quality fix from my local MOPAR 5 star steeler, I had to fix it myself).



Physically, the only problem was a bad wire connection in the harness to the colant temp. sensor, the other fixes were either unrelated or required maintence.



Roughness:

The motor could be running rough because the ECU is seeing erratic engine temperatures from the sensor. The roughness could possibly be from the emmissions system staying in a closed loop because the computer sees the motor is not coming to full temp and is playing with injection and richness timing. Remeber, there is no oxygen sensor to measure effecency of burn so it (the computer) has to depend on other sensors to determine how to manage the engine. I think I remember my engine running rough when I had that problem, but I have put 40,000 miles on my truck since then.



-Rich

P. S. if you need any more help or images out of the service manual, please ask. E-mail me at -- email address removed --

Daddy wrote on 01-17-2003 07:02 PM:

What did you do to resolve your temp gauge problems? I am having the same trouble. My truck also runs rough while this is going on but once fully warmed up the gauge seems to get steady and it runs smooth. Please help. Thanks

 

[Daddy]

Where did you get a new harness connector? Do you have the part number? Sounds like you have the answer. Thanks, I hope it works.

 

[rkressg]

I got the connector from Mopar. I will have to look through my invoices when I get home from work tommrow. Hopfully I still have the part # and price. I do not believe the part was very expensive and that fix only took 5 min.

But I will have to check.

-Rich

 

[Daddy]

I would like to put this back up at the top to see if I get any more input. I think I might have it figured out thanks to RGilbert, I am going to get the new coolant temp connector tomorrow. I post the results of that.