Temp sending unit questions.

[Mosinguy]

My mpg sucks. I drive a '92 Ranger with 106k on it. 3.0 engine. I'm in the process of replacing tons of sensors when money allows. My temp gauge doesn't work and am wondering if maybe my engine is always in a closed loop since the ECM doesn't know if the engine is warm or not. I noticed my sensor still has a lot of thread poking out of the thermostat housing. Like maybe an inch of thread sticking out. Is that ok? Could I tighten it all the way down and be alright? Would that help ensure the computer knows the engine is warm?

I know that won't fix my gauge reading, the other sensor on the thermostat housing is supposed to cover that. But I'm just wondering since the engine runs a bit rough and that fact I'm getting roughly 8 mpg now that it has gotten colder that maybe the ECM doesn't know that it can let off the choke now.

Also, there is a backstory as well. My uncle owned this truck before me and he was the original owner. He told me that is it is really cold out and you give the truck a lot of gas to get moving, the engine would flood. Would that help indicate a bad temp sending unit as well?

 

[snake]

Are you sure the engine is warming up? Might be an open thermostat and the gauge is right. Grab the upper rad hose when its been running for a bit and see. Also, does the truck have good heat? If it is warming up you are probably correct that the temp sensor is faking out the computer, and yes- that would make it run rich and you'll get crappy mileage. As long as the temp sensor is in the water it should work, but be careful threading it down too far as you can split the housing if it gets too tight. But 1 inch of threads? Makes me wonder if the wrong temp sensor is in there. The cold flooding could be closed loop problems from false temp readings, or faulty fuel pressure regulator. Fix what you know is wrong first though, see if the engine is getting hot and if it is get that info to the computer. Running rich will eventually kill your cat so the sooner you fix it the better.

 

[Mosinguy]

Yes I have very good heat. I'll try tightening it down and seeing if it will go in easily. Hoping that is the issue.

 

[RonD]

ECT sensors rarely fail, not never just rarely.
ECT sensors has 2 wires(for computer), Dash board temp gauge sender has 1 wire, other than that they look similar.

ECT sensor has a "pipe type thread" so it is tapered to seal as it screws in, so some threads will be visible.
ECT sensor is easy to test with an OHM meter, read values here:
http://oldfuelinjection.com/?p=28

Open Loop is when engine is cold and "choke settings" are being used, i.e. rich mix, advanced timing and high idle.
If idle is high when first started(900rpm) and then drops as engine warms up(750rpm) then ECT is working, this sensor is the computers only source for engine temp, so if IAC valve is opening and closing the ECT is working.
Bad ECT will also turn on CEL(check engine light).

Closed Loop is when engine is warmed up and O2 sensors are used to fine tune fuel mix.

Fuel pump regulator(FPR) is a more common issue when MPG goes down.
It is on the Fuel Rail and has a vacuum line attached, if the FPR diaphragm starts to leak, fuel will be sucked into the intake manifold via this vacuum line, send MPG down and flooding is more likely.
Remove vacuum line and check it for fuel or fuel smell, replace FPR if there is fuel in there.


Remove the 1 wire on the temp gauge sender then turn on the key, gauge should go all the way up or all the way down, now with key still on connect that wire to a ground, gauge should now do the opposite of above, go all the way up or all the way down.
If gauge does this then replace sender.
If gauge doesn't move then wiring is the issue.

Never use "sealing tape" on a 1 wire sender, the threads are the Ground for this type of sender, so they need a good clean connection to the engine.