Squirley Coolant temp

[Jaxx_]

The gauge cluster uses a separate circuit and sensor to show temperature.

Regarding your follow up question: the coolant temp sensor is kinda an independent circuit from the rest of the grounding plane. In essence, the ground for the sensor is at the ECU(pins 2,14,24). The signal wire goes from the ECU to one side (doesn't matter which) of the CLT connector and then the ECU looks at the resistance between pin 45 and the ground pins. If a connection is bad and/or disconnects, the resistance will rise. As you might have seen from your tests in an ice bath and boiling water, the sensor reads a higher resistance (more ohms) at lower temperature. If the connection has failed or is near failure, you would expect temperature to jump to lower values than actual (176F to 100F, for example).

If you discover there is a connection issue with the tests, you can then isolate one side of the connector to test ground, and the other side to test the signal side. You need to identify the signal side of the connector and the ground side of the connector, then test them.

Do this:
disconnect the ECU.
disconnect the coolant temp sensor.
Find continuity between the ground pins (2/14/24) on the ECU and the ground wire on the connector to the coolant temp sensor. It will be one of the connector's pin receptacles or the other.
Once finding continuity for the ground pins to the CLT connector, you can then assume that the other pin receptacle on the CLT connector is the signal wire.
Find continuity between the signal pin (45) on the ECU and the signal pin receptacle on the connector.

Once you have found continuity at both, you want to confirm continuity for each circuit as you wiggle the harness across the engine bay, especially where you've made your repairs. ANY breaks in continuity or changes in the resistance not caused by your multimeter leads losing connection means that there is a break in the wiring harness for that circuit, and needs to be repaired. Remember that just because you find ONE break in continuity does not mean that fixing that will solve the issue. The other side of the circuit must also be confirmed.

I hope that makes sense. If you can't find any issues with the car cold, plug everything back in and run the motor until the issue appears and test again. If you have alligator clips or an extra pair of hands, it helps a lot. Someone to hold the DMM while you wiggle the harness or vise-versa. If you DMM has a mode of audible buzz/beep for continuity, it will help too.

[Nitro Nick]

Unless there has been a failure, the stock wiring should work fine. After all, thousands of stock e30s use it without issue.

As others have suggested, you should test the sensor before simply replacing it. Measure the resistance at room temperature, in an ice bath, and in boiling water. Make sure to keep the connector area dry as the water might throw off your resistance reading. The readings you listed before were probably an order of magnitude off or so--as in the multimeter was auto-ranging. You need to note if it says Kohms(kiloohms) or anything other than just ohms.


solder is super brittle, your fix may have cracked and come apart. A high quality crimp with butt connectors is more reliable. Thicker or thinner gauge for this application won't matter too much. Even 22ga is fine. The factory size is roughly 25ga wire.

With the ecu disconnected, disconnect the coolant sensor and connect a jumper between the two female pins on the harness. A paperclip will probably work. Then, with a multimeter, test for continuity and resistance (ohms) between pin 45 and pin 2 at the ECU. Also make sure the value is roughly the same as pin 45 and pin 14, as well as pin 45 and pin 24. Have a friend wiggle the harness at the motor and c191 while reading the value across the pins to see if there is a poor connection.

pins 2/14/24 are all on the ground for the coolant temp sensor. Coolant temp signal in is pin 45.

Thanks jax. Ill have to try this test. I got a new sensor and did some of my own testing with the ice water bath, ambient and warmed up temps. I think my numbers were relative to the drop down selection that nando is referring to. When I tested the one currently in the car before the new one was installed the ambient temp ohms were off the chart, which im thinking may have been a bad sensor. When I put the new one in and re-calibrated it seemed to be working well BUT. when the car was warm the same thing occurred. The MS gauge would read 100 Degrees F at fully warmed up temp (roughly 176oF) and during driving it would go back and forth from 100 to 176 on the MS table gauge(during these trips the cluster gauge read perfect warmed up temp). Which leads me to think there is some sort of issue with the wiring. Whether that be a ground or the signal wire. So I am going to perform the test you suggested and see how it goes. Will that test identify if its the signal wire or a grounding issue? Or will that just tell me in general if its a wiring issue...

Thanks again...i'm almost there with this lol

[nando]

I have found that the stock MS calibration for the coolant thermistor is spot-on. I also have an aftermarket coolant gauge in the car; they always show the same temp.

it should be - I made it. :p

[Digitalwave]

I have found that the stock MS calibration for the coolant thermistor is spot-on. I also have an aftermarket coolant gauge in the car; they always show the same temp.

[Jaxx_]

Well this issue has raised its dirty head again. I thought that I had fixed it with the wiring issue but I think that was only half the battle. Now I need to test the gauge with a multi-meter to see what the resistances are. I feel like the drop down select data for the CLT in megasquirt might not be correct. Either that or I have a bad sensor. Going to get a new sensor and and do some resistance testing and then input the values and install the sensor.. Anyone else ever have resistance problems with the stock wiring ?

Unless there has been a failure, the stock wiring should work fine. After all, thousands of stock e30s use it without issue.

As others have suggested, you should test the sensor before simply replacing it. Measure the resistance at room temperature, in an ice bath, and in boiling water. Make sure to keep the connector area dry as the water might throw off your resistance reading. The readings you listed before were probably an order of magnitude off or so--as in the multimeter was auto-ranging. You need to note if it says Kohms(kiloohms) or anything other than just ohms.


solder is super brittle, your fix may have cracked and come apart. A high quality crimp with butt connectors is more reliable. Thicker or thinner gauge for this application won't matter too much. Even 22ga is fine. The factory size is roughly 25ga wire.

With the ecu disconnected, disconnect the coolant sensor and connect a jumper between the two female pins on the harness. A paperclip will probably work. Then, with a multimeter, test for continuity and resistance (ohms) between pin 45 and pin 2 at the ECU. Also make sure the value is roughly the same as pin 45 and pin 14, as well as pin 45 and pin 24. Have a friend wiggle the harness at the motor and c191 while reading the value across the pins to see if there is a poor connection.

pins 2/14/24 are all on the ground for the coolant temp sensor. Coolant temp signal in is pin 45.

[Nitro Nick]

Well this issue has raised its dirty head again. I thought that I had fixed it with the wiring issue but I think that was only half the battle. Now I need to test the gauge with a multi-meter to see what the resistances are. I feel like the drop down select data for the CLT in megasquirt might not be correct. Either that or I have a bad sensor. Going to get a new sensor and and do some resistance testing and then input the values and install the sensor.. Anyone else ever have resistance problems with the stock wiring ?

[Nitro Nick]

Well. I finally put this one to rest. Posting if anyone else may have encountered this or a similar problem. As I traced the wires I found that someone had bypassed one of the two wires from the CTL to the ecu. The problem with that is that they used some shotty butt connectors and did a pretty bad job. Also they used about a 16 ga wire and the sensor uses a 20 or 22. When I rewired them using new butt connectors it actually made it worse, which I knew wasn't a good idea anyways. So I ended up getting some 20 ga wiring and soldering each end. So far the coolant temp corresponded with the gauge and when warmed up read about where it should be. I haven't checked it vs a laser thermometer but it seems to be pretty close and consistent. I however did not find this connector with the illusive C191 plug. It may even have been cut out and all of the harness and sensor wires just soldered together. I found one that was up near the fuse box but not one underneath the manifold. I didn't dig in too much because I solved the issue but I know that has been a common failure point in these cars due to exposure to the elements and engine heat. Moral of the story, trace the wiring, use the same gauge wire always (numerous stories of poor resistance using different sizes) and solder your connections. Soldering is very easy and makes a big difference. Hopefully now I'll be able to tune this beast properly and get it to some meets this summer. Thanks to all the people that commented and tried to help.

[Nitro Nick]

Hey Guys. Looking to have some light shed on this issue I am still dealing with. I took a break form the car for a bit to focus on the house (many of us have). But I am looking to tackle this issue. I had contacted Whodwho who told me to check the wiring. This is what he said

"If is is a late model it maybe a bad connection at the connector under the intake where the injector harness plugs into, it is known to corrode. It is the c191 plug and very common to corrode if you do a search, it depends on the amount of corrosion it can just resistance and would change values. If your car has the injector connectors in a strip that pops off then that injector harness connects to the engine harness under the intake manifold(pic attached). If it has individual connectors per injector then it may not have that connector

http://www.geocities.jp/e46m3c/images/IMG_7133a.JPG "

Has anyone else had issues like this before. And I haven't checked but today I will but I thought I had looked for this connector before with no luck. Also, is there any way of bypassing this and rewiring it to the connector that supports the ECU?

Thanks.

[Nitro Nick]

Yes a multimeter set to read resistance (Ω or ohms) touch both pins with the two leads from the multimeter when the car is cold and again when hot. Were looking to see that the values change. Lmk how that goes and ill walk you through checking the harness.

I am going to run some tests like you suggested. Also I hit up whodwho who built the megasquirt for me and his said some of the wiring could be bad or a corroded connection. I am going to do both.

[Nitro Nick]

If the sensor changes resistance with temperature it works. You need to work out the calibration, weather by finding it using the part number or experimentation as above and putting it into mega squirt properly. It's how it knows what temperature it is.

Since the sensor seems to be working with the adjusted readings. I am now interested in the wiring from the sensor to the ecu...I think this could be the possibility of the fault. But I Also agree the calibration could be the issue too. Looks like some research is in line...

[e30davie]

If the sensor changes resistance with temperature it works. You need to work out the calibration, weather by finding it using the part number or experimentation as above and putting it into mega squirt properly. It's how it knows what temperature it is.

[Nitro Nick]

All you need to calibrate the sensor is 3 known resistances at known temperatures. Many times i have calibrated my own coolant temp sensors using a thermometer, a fridge and a cup of hot water.

Put temp sensor on kitchen for next thermometer, after 15mins measure resistance and take note of temperature. Now put them both in the fridge, wait 15mins or so. check temp and resistance, now put them into a cup of boiling water, bit trickier this one as the temperature will drop reasonably fast. monitor the temp and resistance and get a third temp and resistance.

Now you have 3 temps and 3 resistances. this should get you within about 5-10% error. Good enough for an tuning. Put into calibration into megasquirt calibration. Happy Days.

Or get the part number off the temp sensor, google it, get the data sheet, and use the values in data sheet. But wouldn't that be a bit boring?

Honestly I just want to make sure its working...if not Ill buy a new one. Im way over worrying too much i Just want one that works. i need to find out if its the sensor or the wiring...

[e30davie]

All you need to calibrate the sensor is 3 known resistances at known temperatures. Many times i have calibrated my own coolant temp sensors using a thermometer, a fridge and a cup of hot water.

Put temp sensor on kitchen for next thermometer, after 15mins measure resistance and take note of temperature. Now put them both in the fridge, wait 15mins or so. check temp and resistance, now put them into a cup of boiling water, bit trickier this one as the temperature will drop reasonably fast. monitor the temp and resistance and get a third temp and resistance.

Now you have 3 temps and 3 resistances. this should get you within about 5-10% error. Good enough for an tuning. Put into calibration into megasquirt calibration. Happy Days.

Or get the part number off the temp sensor, google it, get the data sheet, and use the values in data sheet. But wouldn't that be a bit boring?

[Nitro Nick]

Yes a multimeter set to read resistance (Ω or ohms) touch both pins with the two leads from the multimeter when the car is cold and again when hot. Were looking to see that the values change. Lmk how that goes and ill walk you through checking the harness.

So I took some readings today. I'm not the most advanced with the multimeter, but here area the readings:

Cold: 3.18
Hot: .24
Wiring from plug to connector: 8.35

[kyleconstantine]

I'm not too familiar with how to go about testing this. Im guessing you would use a multimeter and post the numbers. assuming the sensor is good do you know which pins on the harness are for this sensor on the ecu to test? This is really messing with the car because it assumes the car is only at 70 degrees F and in a warmup loop...

Yes a multimeter set to read resistance (Ω or ohms) touch both pins with the two leads from the multimeter when the car is cold and again when hot. Were looking to see that the values change. Lmk how that goes and ill walk you through checking the harness.