ECT voltage versus temperature | Ford Explorer Forums - Serious Explorations

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ECT voltage versus temperature


New Member
September 11, 2013
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City, State
calgary alberta
Year, Model & Trim Level
98 explorer
ECT voltage versus temperature


Hi everyone
Im new here. I hope someone can confirm my findings before I spend my money. Ive got a 98 explorer 4wd 4.0L SOHC engine code E. My truck has a idling issue when cold .It searches till it reaches operating temp. The ECT signal to the ECM is clean . With it unplugged, at the sensor , the voltage at the ECM ( back probing the green /red wire)is 4.75 v with the ECT connector shorted (with a cotterpin) the voltage is 0 . I see this on the scanner . The problem is the ECT temp on the scanner does not change . The IAT react like it should -40 to 240 degrees . Im thinking the ECM is fried. Anything else to check before purchasing an ECM ? Has anyone run into this before . In the morning the scanner says the temp is higher then what it really is and the fuel trim numbers indicate running lean. The ECT voltage is in the right neighbourhood .

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Welcome to the forums!

I've found on my scanner that not all the readings are correct. I don't think it's a bad PCM, I think it's just an incompatibility with the scanner. The symptoms you describe make me think you have a dirty IAC, bad O2 sensors or a vacuum leak. What is your fuel trim at? Does it change once the engine is warm?

searching idle

The fuel trims return to normal after warmup. O2 s swing properly. When the truck is warm I clear the codes ( P00171 and P00174 bank 1 and 2 lean) Im good for a few cold rough starts , a couple days , till they show again

I'm thinking you might have a vacuum leak when the engine is cold only. Try checking the vacuum with a gauge when cold and warm. Don't trust what the scanner tells you the vacuum is at.

Thanks for the suggestion I will try that on the weekend but with the compensation that takes place while running rough and unstable the IAC takes the idle from 400rpm to 1800 or so . Im thinking the vacuum will also come and go will it not, Do you think I will get a true picture ?
I have tried running acetylene around the intake like in days gone by with no reaction when cold .