Squirley Coolant temp

[kyleconstantine]

Check the actual sensor. There are 2 coolant temp sensors. You want to check the one with 2 wires as your single wire is working right. Check the resistance between the two pins right on the sensor when the car is cold and again when its hot. Post the values here...should be similar to the values posted before. If they come out right we can unplug the megasquirt ecu and plug the sensor back in and probe the ecu harness pins to make sure the same values are reaching the ecu. Lmk what you find or if you need me to explain any of the steps further.

[Nitro Nick]

Check the actual sensor. There are 2 coolant temp sensors. You want to check the one with 2 wires as your single wire is working right. Check the resistance between the two pins right on the sensor when the car is cold and again when its hot. Post the values here...should be similar to the values posted before. If they come out right we can unplug the megasquirt ecu and plug the sensor back in and probe the ecu harness pins to make sure the same values are reaching the ecu. Lmk what you find or if you need me to explain any of the steps further.

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...

[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.

[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

[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]

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]

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]

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...

[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]

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]

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]

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 ?

[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.

[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.

[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