Well after cleaning all the electrical connecters to te ESA on my 87 D150,doing a complete tune up, fluid and filter change, the truck idles and runs great except for the lack of timing advance.Upon using the search function on this forum which I highly recommend I am leaning towards the coolant sensor.I came to this conclusion after confirming the vaccum transducer is holding vaccum with my hand pump.I have read that this sensor,if bad,will cause the computer not to advance timing and prevent converter lockup.I feel a 20.00 sensor is a better gamble than a 200.00 reman ESA.I usually don't like to throw parts at a problem,but I don't have a FSM,or any way to diagnose this system.

You can usually check these type of sensors with a meter and take most of the guesswork out of it. It might be worth getting ahold of an FSM.

You really need a FSM if you are going to try and keep the ESA. 1987 was the only year that the computer controlled the torque converter lockup. There are diagnostic instruction in the service manuals and a 1987 FSM should be fairly cheap.

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Casually looking for a Clifford hyperpak intake for cheap.