Need help with coolant temp sensor

[corolla_lover]

Hello everyone, i have ran out of ideas of what this problem can be and i have ran out of resources.

Some background on the issue:

-It is a problem with a completely stock 1986 GTS (with the 4age engine) Hatch no modifications
-I recently took the motor out and put it back in after cleaning it up a little bit and cleaning the engine bay
-When i put the motor back in it stalls, is hard to start and runs rough until it gets warm until it warms up
-Once it warms up the check engine light still persists but it does run quite well
-It has a check engine light on and when i checked it i got four blinks which from looking at many different charts it says it is an engine coolant temp code
-I have checked the resistance of the ect sensor and it checked out but just to be sure i replaced it and still no success
-I have looked at the wiring for any damage or loose connectors anywhere and it all looks good
-I have put in a spare ecu i had with the same results


I have tried looking for a good wiring diagram so i could test the wires with a multi-meter but i have had no success finding one that is accurate.

If ANYONE has any help it would be appreciated
Thanks and hope to have this sorted out so i can enjoy the warm weather in my 86

[jondee86]

The information I have says that for a standard Toyota THW sensor the reading
between the ECU pins (back probe the connector) with the sensor hooked up and
the ignition ON, is 0.4-0.7V at 80 degC. The resistance of the sensor at that temp
would be around 0.4 kOhms.

NB: Diagram shows IAT sensor and THA pin, but you are testing THW and E2. The
inlet air temp and water temp sensor circuits are identical. THW is ECU pin B10
(green wire) and E2 is pin A12 (brown wire).

Cheers... jondee86

[totta crolla]

Make sure that all of the air is out of the coolant system, always bleed the system with the heater in the 'hot' position.

[morgan]

Verify the wiring isnt broken or cracked by testing the continuity between the sensor plug and the ecu plag

[aaronlee133]

what totta said above - if you took the engine out did you
burp the coolant/radiator and have the car somewhat angled up on jacks or on drive way to assist with getting the air up and out? air pockets may prevent coolant from properly reaching the temp sensor and hence the ecu may not be getting a correct reading. but something else appears to be the culprit as well. that wouldn't affect the engine having a hard time to start and running rough... is there something else you touched/disconnected or messed with during your clean up like the distributor? what you described sounds like more than 1 issue even though the diagnostics is flashing coolant temp sensor only.

[corolla_lover]

Thank you for all the help and suggestions !! I have not had much time to look at it laity but i will say all the air is out of the cooling system. I forgot to mention i did do the timing belt when the engine was out.

That being said this weekend i checked the marks for the cams and the crank and they seemed to line up perfectly. I also checked the compression and the compression was around 170psi on each cylinder. After i checked those things i wanted to mess with the distributor, previously i set the timing at 10 degrees btdc with the engine in diagnostic mode. When i started to play with the distributor it fired up again.

I looked at the diagram however i cannot find a good diagram of THA or E2 on the ecu, it seems like all of the diagrams i found of the ecu are different however when i have more time i will pick a couple diagrams to use and see what i get.

With that being said i do believe it is an ignition problem weather it is not getting the coolant temperature sensor signal and throwing off the electronic advance for some reason or there is something wrong with my distributor. If there are any other suggestions/ideas please let me know because i am really looking forward to getting my 86 back on the road.

[86 Corolla]

I added a bottle of Water Wetter in my coolant to help rid of the bubble hot spots trapped in the head.

[corolla_lover]

Well i have fantastic news, i have finally found the culprit!!

To start off with i found an actual good complete diagram that i plan to scan in when i have more time. It was after that i realized that i actually had the variable intake actuator/solenoid plugged into the coolant temp sensor, because they are the same connector and they are close in proximity to each other. (the coolant temp sensors wires are green and brown in color) regardless my mistake i switched the sensors and thought i had found my problem and fixed it however with the same code showing it was obvious something was still wrong. I spent another couple hours testing voltages with a multi-meter and everything looked fine except around the coolant temp sensor, but i thought since that was new that couldn't be a problem. Finally i measured the resistance of the sensor itself and found out it was shorted out. I put a 1.2k ohm resister in the connector and the light went out and it fired right up.

Let this be a lesson to anyone always label sensor wires and test parts even if they are new. Thank you for everyone's help and i will scan the diagram and add it to this thread whenever i have time.

[ae86cali]

I been trying to get my account active to tell you that, that was ur issue, with the connectors. However now that you found out the connectors were swaped. You still have that check engine light code. The reason you still have that is because there is a resistor that blew in the ecu. If you were to open the ecu u will see the burn resistor. You can buy one at frys or electronic store, or get a donor from another ecu and replace it.