I have a '92 ranger 4.0, which misfires at idle (warm or cold), and during a cold start it needs throttle input to start and to stay running for the first few mins. Have changed plugs and iacv. Warm start it stumbles a bit at idle but eventually smooths out and doesn't need throttle. Thinking of doing plug wires as well, and just read about a engine coolant temp sensor that tells the pcm whether the engine is doing a cold or warm start and adjusts the iacv and fuel mix to compensate. Just don't want to keep throwing parts at it with no change. Only has 170k km on it.

 

There are two coolant temp units on Fuel Injected engines
ECT sensor, 2 wires, 5volts, only used by the computer
Temp Sender, 1 wire, 12volts, only used by dash board temp gauge<<<this one has been around since the first water cooled engines, lol

ECT sensor tells computer when to Choke a cold engine and how much Choke to apply
Choke means to run Rich with higher idle, but can't use a Choke Plate on EFI, no Jets like on a Carb, so ECT sensor is used for that

It does read like ECT sensor is reading false higher temp, so computer just thinks its a warm restart every time, if ECT sensor was bad it should set a code, but sending the wrong temp won't set a code, computer doesn't know its been off for 10 days or 10min

You can test ECT with an ohm or volt meter, values here: https://www.explorerforum.com/forums...art.24365/full
ECT gets 5v with key on on 1 wire then sends back voltage to computer on the other wire
You can use sewing needle to pierce one wire and with engine cold Key On test voltage on the wire, if it 5v thats the IN volts, if less then thats the OUT to computer volts, the one you want
50degF = 3.5v
70degF 3.0v
ect

140degF is when computer no longer Choke the engine
So if you see under 2volts and engine is cold then ECT is bad

 

Yeah I knew about the temp sender, but never knew it would need another sensor to tell the pcm the same thing the other sender would. Maybe more accurate? Who knows. I'm more of an old cummins guy myself, all mechanical. Just peeked at that chart, is there any difference below 50 degrees? Or does it treat 50 degrees the same as -10?

Edit: also does seem weird that the pcm wouldn't take in both the sender and sensor values and compare them, to check if there is a big difference that would cause an issue.

 

No connection between the 2 temp units, one for computer and one for the dash, while yes they collect the same info, they are totally different as far as the "signal" they can provide

In the mid 2000's Rangers lost the temp sender when they were changed to Digital Clusters(HECs), the computer still used the ECT sensor for temp and then sent that info as a data stream(1's and 0's) to the digital cluster to be displayed as Engine Temp on the gauge



Ford senders use these values: https://www.vintage-mustang.com/cdn-...7-jpeg.827352/

And up until the advent of plastic intakes and other engine parts, lol, the Senders used their threads as the Ground to complete the 12volt circuit, there were 2 wire senders used after this "update"
So a ground difference or 12v issue would cause sender to be inaccurate

ECTs are more accurate even with 5volts because they use a common ground and 5volt in the computer, 2 wires
5v power supply is in the computer and that powers all the sensors, also common ground in the computer, and then one return wire from each sensor, so return voltage can be compared to the 5v and ground to get an accurate voltage difference from each sensor