It must be something inside the EEC,
I think I educated myself about how the ECT circuit works.
I checked the resistance between pin 7 and the ECT connector and got 1.5 ohms, thats with the computer disconected.
I plugged the computer back in and checked the voltage KOEO at Pin 25 (ACT) got the same 3.98 volts with the sensor disconected.
I checked voltage at pin 26 (VREF) and I get 5.03 volts, thats with all the sensors on that cicuit connected.
Is it the same vref regulator in the eec that generates both vref voltages for pin 26 and pins 7 and 25?
How do I find when I pull the EEC apart?
Could something be causing a voltage drop between the regulator and pins 7 and 25 but not pin 26?
I guess I should sum up the current problem with this car.
Ive had the car for 15 years and it never ran right. Always crappy when it was cold.
Pulled the engine and tranny out about 5 years ago and figered if I replaced most everything, it should run fine.
Didnt happen
Still ran crappy
Last year I decided to make it my mission in life to get the car to run like new.
Started with the codes that were coming up.
Went through all the emmission stuff, found a couple of vacuum leaks and fixed those.
Found a burned up O2 harness that a previous owner had patched back together.
Replaced that and was at last code free, 11s all around. (I ordered a manual harness and installed it, I figured out it was an auto harness they sent me. I repinned the harness and I checked for a burnt trace but the eec didnt have one, could still pull codes no problem)
Car still runs like crap.
I have since replaced or checked every sensor and wire and component on the engine.
One of the things its doing is when its left sitting overnight and is cold, it stalls after I start it.
if I keep my foot on the gas I can keep it running, after a few minutes it warms up and idles on its own, but pops and hesitates untill its at operating temp, but still runs crappy.
I have found a whole bunch of threads on the stalling on a cold start issue, but very few solutions
I have a SNEECIV datalogger and noticed that the temp of my ECT and ACT sensors were reading 55 degrees, when it was below freezing in my garage.
I removed the sensors and tested them at different temperatures and they checked out fine.
So I checked the voltage at the sensor, and when I got 3.98 volts I ended up here.
I just changed out the computer with a Cardone remanufactured one from Rock Auto. That computer has the same low voltage at those two sensors.
Either Im really unlucky and got a bad computer from rock auto, or something fried my new computer.
Wish I had a freind that lived close with a known good computer, but no such luck
AS I side note, I confirmed that the low voltage is causing the car to stall when its cold.
I unplugged both sensors, leaving the computer reciving 3.98 volts at pins 7 and 25.
This is the voltage the computer will see when its 29 deg, or at least thats what my SNEECIV read it as.
It was about 29 deg in the garage and the car started right up and purred like a kitten.
looking at the different voltages from the chart here
Ford Fuel Injection Engine Coolant Temperature Sensor (ECT)
I assume the wrong voltage is causing the EEC to use the wrong timing and fuel tables and the car stalls.
The cold weather really seems to agrevate the problem, perhaps because the voltage is so different at low temps?
I hope I have found the cause of one problem, now just need to find the solution.
Are, my conclusions wrong about this?
What do I do now?