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Old 08-09-2008, 10:10 PM   #1
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Default Coolant Problem W/ GM Sensor

I have a MS2 standalone and I'm running a GM coolant and air temp sensors. After cooling completely, the sensors agree with each other perfectly. Air temp sensor seems to work great.

Coolant sensor is showing really high values as the motor warms up. At first I thought it was overheating. Fans are working properly and are running when MS2 sees coolant temps above 170. However, I'm seeing temps of 230-245.

I have no idea why though. My motor is not overheating. I drove it and it seems fine. Stopped several times to check on it and it's not overheating or boiling over, etc. Runs fine, but guage in Megatune is showing 230-245. I removed the stock coolant sensor so no dash guage.

I'm running the 2490 ohm bias resistance. I have what should be a good coolant sensor that's <1 yr old, though I could change it as it's relatively inexpensive. All grounding should be perfect right now as I rewired the car. (watch my wiring somehow be the problem). Right now all sensor ground and MS grounds go to the same bolt on the back of the cylinder head. All relay grounds and any high current device grounds go to a separate lug on the back of the head.

Values in themistor Table
Degrees C* Ohms
-40 100700
30 2238
99 177

Any ideas?
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Old 08-09-2008, 10:51 PM   #2
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You do have the new inc. files in your mtCfg folder too, right?
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Old 08-09-2008, 11:01 PM   #3
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Quote:
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You do have the new inc. files in your mtCfg folder too, right?
I have no idea what you're talking about. FWIW I'm MS2

I had the fuel injector setting way off. I had them set for high not low ohm injectors. I fixed that and it idles better, but guage still reads high.
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Old 08-10-2008, 08:07 AM   #4
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I'm not sure how MS2 works but with MSI when you create the inc. files with easytherm you put one set in the src folder to burn to the MS and another copy of those into your mtCfg folder. The 2nd set tells Megatune how to calibrate the gauges in it to match what MS is seeing. Again, no idea if this is how MS2 does it. AbeFM?
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Old 08-10-2008, 02:42 PM   #5
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I don't know! I have this problem too, it's way, way off. I've been meaning to go through the wiring, but really... The way the MS-IIe people are, you never get a straight answer out of them - even if they know they are wrong.

My fix, and it's not a good one, is to change "99" to "82".

I'm sure there's a set of numbers which will work - but that makes it read about right in a 20* window near my opperating temps, and it keeps my fans on when I need.

It's VERY interesting you see this on the GM sensor, I thought it was something to do with the miata one. Which wiring do you use?!

I measured my sensor with joe's help, that still fixed nothing.
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Old 08-11-2008, 02:20 AM   #6
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Well it is POSSIBLE that the back of the motor is that hot. I don't have a reroute. Maybe the back of the motor just stays damn hot. I have my heater core bypassed right now too. I see 230-240 all day long so far. Car never boils over and seems fine, but damn it sure reads hot. The fans run all the time as they are set to come on at 200*F. Water exiting the upper radiator hose isn't that hot. I mean, it's warm in comparison to the water that's circulating through the hose that bypasses the heater core. Maybe it really is that hot back there. This can't be good. The entire engine is rewired, so I used my wiring. It has one wire to "coolant sensor" in the MS wiring harness, the other to ground on the back of the head.
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Old 08-11-2008, 02:58 AM   #7
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I have no solid reason to believe the MS-II correctly reports coolant temps. Many things on it don't work as advertised, and I don't know of ANY MS-II's which read correct - not that I know of many that read incorrectly, but still. :-) If you figure it out, let me know. You could always drop the sensor in hot water to calibrate it.
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Old 08-11-2008, 03:20 AM   #8
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Quote:
Originally Posted by AbeFM View Post
Many things on it don't work as advertised, and I don't know of ANY MS-II's which read correct - not that I know of many that read incorrectly, but still. :-)

I sure want to switch to MS-II soon.
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Old 08-11-2008, 09:15 AM   #9
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I'd recommend measuring the actual resistance values on the sensor using ice water and boiling water, and see if calibrating it to those values does the trick.
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Old 08-11-2008, 09:29 AM   #10
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then, IIRC, MSII has instant calibration to the sensors in some option....much like the TPS.
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Old 08-11-2008, 02:26 PM   #11
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You don't need easy therm, that's correct, you type in the three numbers, and it uploads them. Unfortunately you can't build them into the /msq file, though, so you reflash and sometimes forget the temps read way off.


Matt, you guys have any MS-II's with good thermo tables? I think if you measured the values WITH the MS you'd be in good shape. Joe and I did it at my house, the sensor in water at several points.... And it had all the same issues - so that didn't fix it. :-(
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Old 08-11-2008, 04:52 PM   #12
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This is probably the first I have heard about a GM sensor being off.

Wh built this one Pat?
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Old 08-11-2008, 05:32 PM   #13
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I'll be glad to see this all get sorted out, it's been a background nagging concern for me for a long time
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