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I’m not really posting this as a question, but more as a ‘this is what my plan is, does it make sense?’ My ’91 F150 has the 5.0 V8 and auto trans. Last winter, the thing would start up just fine, but when it was ridiculously cold, it would bog down and die when I went to drive it. I would have to floor the gas pedal (clear flood mode) to get it to start again. The temp gage never gets very high on it, even in warmer weather. I replaced the ECT in the spring, and it seemed to help, but the temp gage is more than ever buried near the low end at best now that it’s cold again here in Ohio. I haven’t experienced the stalling/having to restart yet, so I’m guessing the ECT replacement did some good. When I get time, I plan on running voltage drop tests on the circuit itself looking for corrosion etc… The truck has been TERRIBAD on gas all summer long, even for a truck. Any other suggestions that I might have overlooked? Thanks as always. I’ll keep ya updated.
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Is the thermostat working correctly? If it’s stuck open, or worse broken into pieces (I’ve never seen that on a Ford, but have seen it on several Mopars) it may not be letting the engine get to operating temperature which will cause the fuel economy to suffer. Also, have you replaced the O2 sensor(s) recently? It’s been my experience that they’re good for about 100k miles before needing to be replaced. If the O2s are getting sluggish the engine can be running rich for too long before the computer compensates for it.
The low reading temperature gauge leads me to suspect a thermostat problem, or a coolant level problem. I had an F-150 with the same engine as yours (mine was a 1990 with a manual trans) and if I remember correctly the temperature gauge sat right in the middle of it’s range once the engine got warm.
+1 on checking the thermostat, the ECT could be reading fine but if the engine never gets up to temp then it’s not going to run properly. You can think of the ECT like the choke on a carburetor, if it’s not reading right the mix will be all off and
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