Alrighty, so my car has recentely been running like crap, so i decided to see what was up.

I noticed when plugged into Tunerpro that my car constantly read 240.55 deg. farenheit.

My mechanical gauge says the car is still cold, it was.

So i replaced the Coolant temp sensor and its still reading 240.55.

No fluctuation whatsoever.

Any ideas!?

 

Wiring is shorted out somewhere

 

There are two coolant temp sensors. One runs the gague on the dash (single wire sensor in the driver's side cylinder head between #1 & #3 spark plugs) and one that runs the ECM (2 wire jobbie on the front of the intake manifond, pointing forward, I believe). Lots of people have replaced the wrong one over the years.

 

Ive replaced the one with the yellow/black wires on the front of the intake manifold. Im now tracing the wires and i have continuity from the plug to the ecm.

I have no idea what to do. ...

 

I just read that this is a symptom of a bad ECM.

It stays pegged at 240.55

Anyone heard of this?

Also, my car picks and chooses how it wants to run.

 

Also double check your grounds as well, they are located on the back side of the head, on mine it was the passenger side.

 

A pegged high reading is usually the leads shorting together. The connector itself will sometimes go bad. Inspect it carefully. You can also go back to the ECM plug and check for continuity between the leads at the connector.

Intermittent behavior is also a symptom of a wiring open/short.

 

are you using a $32b definition ?

 

you might want to try winaldl for a comparison to see if the reeding is acurate that the ecm is giving, high resistance on this circuit would case a hight ect.

http://winaldl.joby.se/

 

I know you didn't say the check engine light was on, but here's the info on the code for high temp (low resistance.)
Code 14; 284° reported for more than 20 seconds.
Typical causes for this code include:

1) Severe engine overheating
2) Defective Coolant Temperature Sensor (resistance too low)
3) Short circuit in CTS-ECM harness
4) Defective ECM

Throw the sensor in the freezer let it freeze to 0°, the resistance should be around 25k ohms, let it warm up to room temp then put it in boiling water, water boils at 212°, resistance should be around 185°.
If the sensor, and wiring/connections are good then you might have a bad ECM.