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Old 06-11-2014, 09:10 PM   #1
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Cool MS2e Thermistor Calibration

Greetings. In lieu of a signature, here's the gear involved:
1990 chassis
MS2e by Rev
2005 MSM transplant
1.6 CLT
DIYAutoTune GM IAT installed in stock MSM location (just before TB)

Using the following values for both IAT/CLT:
2490 bias resistor
-4/16150
104/1150
176/330

Symptoms:
Both sensors read dead even after the cars been off for 24h. However, at 72* ambient they both read about 56*.

CLT jumps around +/- 10*F at high load/rpms.

IAT reads about ambient during an at temp highway cruise.

Attempts at resolution:
Punched in appropriate values about 100 times as sanity check. No change.
Replaced IAT for *****. No change.
Observed, cleaned engine bay grounds. No change.

Plenty of other threads out there, but those folks seem to have been resolved by punching in the right values, or cleaning up some cabling. I think I'm in the clear on those fronts?

TIA.
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Old 06-12-2014, 08:57 AM   #2
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why are you using GM AIT sensor values for your CLT sensor?

simply pick GM for AIT and RX7 CLT (S4 & S5) for CLT.
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Old 06-12-2014, 09:14 AM   #3
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Doesn't make a difference. Again, at about 68* ambient in the garage presently, I read out at 54*.

I misinterpreted:
DIYPNP MegaSquirt installation for the Mazda Miata

At least for the IAT bit. The CLT values are very close.

So, they're innacurate, but read the same, with the suggested settings.

Off to work...
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Old 06-12-2014, 09:52 AM   #4
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change the bias until it's closer. that way the scaling just gets moved, by the curve characteristics dont change.


otherwise, you'll need to actual test your individual sensors and plug in real values.
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Old 06-14-2014, 01:23 PM   #5
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Dropped bias to 1800 for both sensors. Seems to get them right where they need to be, about 68* in the garage this morning.

Going to trim up the belly pan, get it bolted up and see how things go...
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Old 06-14-2014, 02:03 PM   #6
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yeah, so the actual shape of the resistance curve didn't change, but you moved the "zero point" if you will. Just monitor the temps to make sure it's still good when warm.
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Old 06-14-2014, 11:28 PM   #7
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Was able to verify that things are accurate by watching the gauges, and letting the car warm up from cold.

Got a brief high temp CEL on a quick 1-2 WOT romp, it peaks really fast then cools off immediately as I return to highway cruise. Drained coolant and replaced w/ WW and distilled water earlier today, so maybe just needs burped. I'll keep an eye on it, but it definitely seems stable even on (brand new/re-used) 1.6 OEM cooling gear w/ a 180* thermostat. Slower pulls from highway speed seem okay.

At least I'm accurate, so I can keep proper tabs now.
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