Coolant Temp Sensor Issue

[gvr4737]

So i finally got my car 99% done and running. All has been going well but I ran into my first issue. my wiring on my thermostat housing harness was looking pretty ratty soo i decided to cut it back some and solder/ wire in new wiring to freshen it up . the car was running fine . Than I noticed my temp gauge was not working at all, So i figured i had crossed one of the wires . soo i got rid of my spades and I wired in a new chunk of the harness peice that i got from a local junkyard. Here is my problem, The car will not run with the Coolant Temp Sensor plugged in on the thermostat housing . I can keep the Temp gauge wire plugged in, " single spade on the right of thermo sensor" and ill get a temp reading on my dash, but the temp sensor itself can not be plugged in. The car will just sit there and crank and crank and crank. The coolant temp sensor and the gauge sensor consists of 3 wires... a green w/black, yellow w/green, and yellow w/green . 1 of the yellow w/green goes with the green w/black to the temp sensor and the other yellow w/green goes to the gauge read out for the cluster.

I started tested my harness to see if i was having a short some where since the coolant temp sensor works off resistance... and the wiring seems fine " even though the mitsu manuels dont give u too in depth on how to check it"

does anyone have ANY idea why my car is acting like this and why it wont run with the coolant temp sensor plugged in. Also does it matter which yellow w/green wire goes to my gauge read out sensor compared to the yellow w/ green that goes to the plug for the coolant temp sensor ...


Please Help!!!!!


- Thanks -

Mark

 

[gvr4737]

Also.. Pics/links of this would be helpfull too if u have any


thanks

 

[spoulson]

Do you have a datalogger to indicate what the coolant sensor is reading? One reason you could be cranking is if the engine is flooding from a bad temp reading. You can try unplugging the injectors, crank some more to air out, then replug to see if the engine will truly start.

 

[gvr4737]

i lost my data loggger cable soo all i have to work with is knowledge and a volt/resistance reader


anyone have good tips for testing these wires/ sensors

 

[gvr4737]

I finally got my wiring straightened out where i know its the correct way...

i installed a brand new coolant temp sensor and tested the gauge sensor.. both are perfect condition

turn the key to the car and it still wont run

than i found out this... if i take a peice of wire and connect it to the green w/ black wire off the temp sensor than connect it to a solid ground ... the car will fire right up and work perfect.. let it run for 10 minutes and no CEL yet. Soo is the green w/black wire a ground that maybe somewhere in the harness isnt getting the right connection and cause it to run shitty.. and adding this extra ground to it helps????

any idea's????

i didnt solder in the ground wire i ran off the green w/black yet cause idk if its the proper thing to do


let me know


thanks

 

[powerplay]

 

[gvr4737]

Im guessing that the Green w/black wire is the ground for the coolant temp sensor .. basically their must be a fray/split somewhere in the line and by me running another seperate ground its making up for that

 

[CP]

Just checking: that diagram is for a SOHC 8V. Doesn't he need the one for the DOHC 16V Turbo?

Anyone know the thread pitch on the front sensor with the one wire for the dash gauge?

 

[powerplay]

You are correct. My mistake.

 

[atc250r]

When I first put my GVR4 together I got the wire that goes to the single terminal connector on the back of the T-stat housing and the one on the front of the housing mixed up and switched them. I had the same problem as you're having. You have to make SURE that you don't have those two mixed up. Also, it looks like that diagram only has the one for the ECU's coolant temp sender, not the single wire one that goes to the gauge or the single wire one that turns on all the cooling fans in case of an overheat.

John



John

 

[powerplay]

Per John's comments, this might help.

 

[gvr4737]

yeah ...


well i did the ground test on the two yellow w/ green wires to determine which 1 was the gauge wire and which went with the green w/black to the temp sensor... i grounded the one yellow w/green and than turned the key on .. nuthing happened... than i grounded the other yellow w/green and the needle on the dash moved and pegged the end.. soo that determined which wire was for the gauge read out . soo than i wired the other to to the new connector and plugged that onto the brand new temp sensor installed. still car would not run . im just gonna solder in another ground on the green w/black wire , cause right now i have an aligator clip on a bare part of that wire and to a solid ground and the car runs perfect how it used to run.. the gauge works as it does and the temp sensor is working like it did . Im guessing somewhere within the harness the green w/black wire must have gotten broken down and doesnt have the resistance needed to control the temp sensor

 

Just looking at my wiring diagram, I see that the green with black wire goes to ECU pin 24 and gets its ground from inside the ECU. I'm picking that you had a short somewhere before you found and repaired the wires which burnt the trace on the ECU circuit board from pin 24 to ground. If you feel inclined, pull the ECU and check, bridge out any burnt trace with a bit of wire. Otherwise grounding externally is probably OK, but may allow some slight errors due to current flow in the ECU ground.
Hope that helps.

 

[CP]

Anyone know the thread pitch for the #1 sensor in that diagram...for sure? I want to add an accurate guage there to replace the one in the dash.

 

[iceman69510]

1/8 BSP Cy.

 

The Green/Black striped wire is the SENSORS GROUND from pin #24 of the ECU. If you are NOT getting GROUND on that wire there is a good chance that you have a blown trace in the ECU. You should NOT connect it to a chassis ground, as that can cause a ground loop issue that will throw off your O2 voltages too. You need to see if pin #24 at the ECU is grounded or not.
BTW, that 2-wire sensor with the green/black and yellow/green wires on it has NOTHING to do with the gauge in the dash. It ONLY connects to the ECU so the ECU knows the coolant temperatures. There is another single-wire sensor, with a yellow/green striped wire on it that connects to the dash gauge. /ubbthreads/images/graemlins/wink.gif

 

[gvr4737]

well with it grounded this way everything seems to be working perfect... my wideband is reading excactly what it should be and the temp sensor is working like it did before this issue

 

[atc250r]

That may be but you can still cause other problems down the road. Certain things are not supposed to go to chassis ground and grounding them there can cause damage to other components.

John

 

[gvr4737]

hmm... i wonder why im not getting a ground through the ecu

the wire looks fine .. i pulled back the loom and its all in nice condition

it has to be something with the ecu itself

if i didnt just get a foot of snow id pull the ecu and check it out ...

 

[atc250r]

It could be a bad trace or a failed transistor. I know you've been going through one thing after another with that car and I'd hate to see you cause a problem for yourself like that.

John