Archived temp gauge erratic, runs rough

[Daddy]

I posted this prob. in the 24 valve forum a week ago and only got one response. I still havent resolved this. When I start the truck cold it is running very rough and when it this is happening the temp gauge is all over the place. It seems to go away completely when fully warmed up, and it doesnt do it every time. It will go a couple of days and work perfect and then act up again. The first thing I did was replace the coolant temp sensor, didnt help. Then it was suggested by a forum member to replace the wire connector to the sensor. My dealer couldnt even find the part # for the connector. The forum member got a part # for me and I ordered it but it wasnt right (they must have changed connectors, my truck is 99 I think his was a y2k). The check engine light comes on when its acting up but my 99 wont show the codes on the odometer. I also tried this, when it is running right and you unplug the sensor the gauge goes to 0. When its acting up and you unplug the sensor the gauge still swings all over the place. To eliminate a (short in the connector type) of problem that was suggested to me I even cut one of the wires while it was acting up and that didnt change any thing. Maybe I am going about troubleshooting this all wrong but I feel that I have eliminated the problem being the sensor or the connector. Does the signal go to the pcm or the ecm from the sensor? Could it be another sensor that would seem unrelated but be causing the trouble? Please help, its going to the dealer next week if I cant get it figured out.

 

[B.G. Smith]

Sensor

Sorry I can't help much but I do have a manual for 99. It says "the coolant temp. sensor provides an input voltage to the ECM to monitor coolant temp. The ECM uses this input along with input from other sensors for engine protection, fuel timing and fuel control. " Might check the connectors to the ECM and its mounting, I believe it is mounted to the side of the engine just forward of the fuel filter. bg

 

[bmoeller]

Just a guess since I can't hear it run but, if it runs fine once it worms up, is the cold idle feature turned on? Supposedly when it is on, it only runs on 3 cylinders.

 

[sag2]

Don't have a 99 book, but I'll take a leap that the 2000 is the same. Coolant temp sensor has battery voltage on the black/light blue, and the signal goes in to the ECM on the tan/black wire. It enters the ECM on pin 14. It appears the ECM uses the bus to send the coolant temp to the pcm, which in turn sends it to the cluster(or possibly straight to the cluster).

If you can tap into the Tan/black wire and watch the resistance change as it warms up you would know if it is the sensor or the ECM or the bus. Without a DRBIII it will be difficult to pin it down for sure.

Good luck

 

[15w40]

The coolant temperature sensor in your ’99 connects to pin 14 of the 50 pin ECM connector. The ECM uses this signal to adjust the injection timing and converts the info to a digital protocol on the CANBUS to drive the temperature gauge. To put this in other words, if your gauge is bouncing around the ECM is getting a bad signal from the coolant temperature sender. This causes the ECM to send a timing signal to the injection pump that is also bouncing around and causing the rough idle. My guess is that there is a bad connection somewhere between the sender and ECM. As the engine warms up, the connection gets better and is maintained. Try disconnecting the plug on the ECM and inspect for dirt or moisture. Just taking it off and reinserting it may help. If that does not work, an ohm meter reading from pin 14 to the “B” connection on the coolant sender should read close to 0. Wiggle the wires while making this reading.



Good luck.

 

[Daddy]

Thanks for the responses. Ill check the ecm connection tomorrow. I was hoping someone else had this exact same prob and could point directly to it. Keep the suggestions coming, I will post the cure when I find it.

 

[baby.driver]

If your name was daddy. driver I might show some respect.