The connector hangs off the firewall behind the passenger side fender well.

 

Thanks again. My problem is that I can't drive the truck now, so I can't be on the road to see if it throws a code. It immediately stalls when I put it into gear. It lunges a bit, then dies.
It starts fine, and idles (but it is rough). I would not mind replacing some parts, but I have no idea where to begin--- if I could just get a trouble code, it would point me in the right direction.
Since it idles rough and is stalling, would you all agree that it is likely not the torque converter-- and is more likely a sensor, fuel issue, etc.?

I unplugged the coolant temp sensor, and it did not change anything--- idled the same and then stalled. Is there really a chance that the coolant temp sensor could be causing this stalling?

Can I start disconnecting parts,to see if that changes any of the symptoms?

There is something that is making it stall once I get it into gear----???????

 

Is the TCC staying locked? Might try unplugging the three pin connector on the trans, it's about halfway back, and plugs straight down into the top of the valve body. See if anything changes. If not, I might be tempted to change the crank sensor.

 

It is very unlikely you will have codes now when you didn't have them originally. You only had a mistaken way of seeing the flashes of the chkegn light. My suggestion about the coolant temp sensor is based on your original post where you mentioned flushing the heater/cooling system and changing the thermostat and then had this problem.
Hey You has a lot more experience than I and it could very well be the crank sensor that just happened to fail at that point in time. Crank sensor is on passenger side, back of motor below the oil sending unit poking down into the small hole in the bell housing. It bolts to the block. The recommended method of replacement is to remove the wheel and go in that way.

 

Thanks Gentlemen-- you have given me some things to investigate and try. I will report back.
Can you all confirm that the sensor below is the correct coolant temp sensor that actually feeds information to the ECU? or is this just for the temp guage on dash?
This is a 1994, 3.9 and this sensor only has one wire coming out of it. Thanks!

 

I can’t speak for the 3.9. I changed mine but I have a 5.2. Not a lot of room on the 5.2 but doable. The sensor was on one side of the tranny and the connector on the other side. Not sure what kind of room or routing you have on the 3.9 but consider using the existing wiring on your sensor as a fish tape to run the wire on your new sensor…if necessary.

sorry, I thought I was referring to the crank sensor. Keep this post in mind if you choose to change your crank sensor.

Where are you buying your coolant sensor from?

 

And I agree, Hey You has a pretty good grasp of the electronics so I’d value his suggestions if I were you.

If he suggests something you don’t understand just slap him and tell him to speak in English. He will.

 

Here is a link to rock auto https://www.rockauto.com/en/catalog/...+/+sensor,4748
That list has both sensors. Page 8W22 or 8W23 in my 94 fsm has the engine coolant temperature sensor on the left side, (the other coolant sensor is to the right) if you are facing the front of the engine. I'm pretty sure its the 2 wire sensor but I could be wrong. Click on the pictures and in each picture there are arrows near the top so you can see several views you will see the black ones like the picture you show has 2 prongs and the gray ones have only a single prong. if you click info it will open another page with more info.

 

Thanks. I was also looking at Rock Auto-- but had not realized that there were two sensors there-- a 1 pin and a 2 pin. Yes-- the sensor to the right of the thermostat is a 2-pin (two wires), and to the left is a 1-pin (one wire)---- as one stands in from of the truck and is looking at the engine. I am not sure what I am going to do. I may have to have it towed to a shop, as I really do not want to just throw parts at it. I will report back once the issue is solved.

 

A tow is $???, a mechanic is $95hr plus and the two parts suggested are less than $30 plus delivery.
The truck is 27+ years old, you cold replace every sensor and other replaceable part on it and safely say you were doing maintenance, not throwing parts at it.
But I get it not knowing the problem makes any other effort seem wasted. There was another thread where the guy thought it might be ECT and it turned out he had a blown head gasket.
Good Luck man let us know.