Can somebody tell me what effect unplugging the ECT (engine coolant) sensor will have on fuel mixture, timing, etc?
I have a pesky miss when the engine is cold on my '87 F250, 300EFI engine, with 262,000 miles.. I've done all the usual, and many unusual, tests suggested by helpful people on this forum. It still misses and I've been driving it on as it runs perfectly once warmed up.
The miss is gradually getting worse, taking longer to disappear as the engine heats up, so I'm trying again to find its source. This morning, I umplugged the ECT Sensor, then started the truck. At 28 degrees outside, it was a little slow to start, and I had to keep it going with the accelerator, but it ran great with no miss. I plugged in the ECT and got an instant miss. Unplugged it again, and there was no miss.
I tested the sensor (which has already been replaced once) using Haynes Manual and Charles Probst manual procedures, and it checks out as being okay. Before I spend money trying and buying another one, I would like to know more about how this ECT works so I can try thinking through completely about what is going on here. (By the way, the "computer"/ECM has already been changed)
I'm hoping some of you can help me.

Thanks,

 

The ECT sensor helps the computer in its phases of engine operation, whether it be cold start up, warm, etc...

It controls the computers input for open/closed loop operations...

Have you checked what kind of voltage the sensor is putting out?