Engine coolant temp sensor unplugged

So I've been fighting this truck for 2 years now with hard starting when the engine coolant temp gauge is sitting between the C and the lower line. Like it won't start unless I push on the throttle and then it's still a slow start. Unplug the coolant temp sensor and it starts up instantly. I've changed the the sensor 3 times hoping somethings going to change and it never does. I have watched the live data and with it plugged in it reads the correct temp. Unplugged it reads -40. So this being said I'd rather just leave it Unplugged cause doesn't seem like anything will make it better. I'll post videos of it. The 1st video will be with it plugged in and it wouldn't start until I pushed on the throttle. 2nd video will be right after with the coolant temp sensor un plugged. Oh yeah this is a 3.4L. Update guess I won't post a video it won't work but long story short 1st video cranks for 20 seconds then starts. 2nd video with sensor un plugged cranks one second and starts right up....

 

Your not confusing the sending unit for the gauge with your coolant temp sensor?

Has this problem ever tripped any Help codes in the 2 years it has been a problem?

Have you ever checked any of the senors you removed?

You might be dealing with a simple open circuit or poor connection.

With the Coolant Temp sensor unplugged are you getting the normal high idle at start up?

With your sensor unplugged The ECM will never detect the engine is at the correct temperature .

Good Luck!

 

No codes ever until I un plug it then it throws the code. Checked all the sensors with a voltage meter and they all check out good. Have replace the wiring harness to the sensor with no change. I doubt it'll do the high idle when un plugged. And yeah the the live data reads everything correct when it's plugged in temp wise but won't start then with it un plugged it reads -40 degrees and starts right up. Where the temp gauge is read with a different sensor i can't really fool it and just drove it with the sensor un plugged and truck felt like it had more power.

 

Any after market wiring that might be causing your problems?

This is just one of those strange problems that makes no sense.

Good Luck.

 

Not that I can think of that would affect that. And tell me about it! I feel like a tweaker that can't get his fix! this has been a 2 year obsession.

 

Maybe the pcm is bad

Any chance you're replacing the wrong temp sensor? Where are both sensors located?

 

Is there a way to test it?

 

probably, but you'd need to do some pin-point checks at the pcm connector. And do continuity checks along the entire harness going from pcm to sensor before condemning it

I can look at identifix tomorrow morning when I get to work and see if there's anything that relates to your symptoms

 

@Dm93

 

I really don't think it has anything to do with the coolant temp sensor if it reads correctly, unplugging it make the PCM add alot of fuel because it will either assume the engine is very cold or run in failsafe mode which is also on the rich side.

Check that both the Coolant Temp sensor and Intake Air Temp sensor both read within about 5 degrees of ambient temp after the vehicle sits overnight, if they do then they most likely aren't the issue.

 

I'm out checking the live data right now. With it plugged in my coolant temp sensor is reading 18 degrees and my intake air temp is reading 32. The outside temp is around 25 degrees. And with the coolant temp sensor unplugged and the engine all the way cold from sitting over night it won't start. Plugged it in and starts right up. I just need to tie into those wires and put a kill switch so when it's a certain temperature I can shut it off then turn it back on as soon as the truck is started haha.

 

I really don't think the coolant temp sensor is your issue, the fact that you are unplugging it to get the truck started but it's reading correctly plugged in leads me more toward a base fuel issue.

What do your fuel trims look like under various conditions?

 

I'll look and see. I definitely think it's fuel related too but I've swapped injectors, and newer fuel pump. I haven't done the fuel pressure regulator but id think If if was that the truck would have a hard time starting and running all the time wouldn't it?

 

And im not sure what else would have something to do with the temp and fuel together. Cause it's definitely temp related. It only hard starts in that small area of my temp gauge everywhere outside of that it starts up like a brand new truck and runs great.

 

Here is the live data at the temp it won't start. 1st pic is just the key on to get the numbers. 2nd picture is just as the engine started after cranking for 20+ seconds and I finally gave it some throttle, 3rd pic is it idling after.

 

You would think unless one is leaking with the engine off.

I mean unless the sensor is skewed in that particular range but that would be really odd, I've never seen that before.
Does the temp on the scan tool appear to always be correct?

 

Yeah seems to be right on the scan tool all the time and like I said I've put 3 brand new oem temp sensors in and they all do the same thing at that exact temp range. No start until I give it throttle and even then it takes forever and just kinda stumbles and starts but then runs perfect. Injectors definitely aren't leaking I've pulled them about 15 times to check and they are all dry everytime. The only perk to this is I can swap out a set of Injectors in about 20 minutes now .

 

You said you put injectors in it, were they OEM (not Amazon ebay "oem") and not some amazon ebay trash?

Did anything change after swapping them?

How did this issue originally start happening, all of a sudden, gradually, or after something that was done?

 

Have you checked to make sure there is no gas in the fuel pressure regulator vacuum line?

 

I have a OEM set right from toyota and I have a set from motorwest performance. It seems like it just all the sudden started. And since I've put about $8,000 into the POS trying to get it figured out including a engine rebuild. At this point I really do think I'm going to put a jumper in that coolant temp sensor harness and just shut it off when it's at that temp then turn it on as soon as the truck starts cause at this point I should've trashed the truck and got something else haha