Megasquirt Support Forum (MSEXTRA)

Hello everyone,

I'm not very good in English, so i'll be short. Few days ago i changed my CLT sensor, that was reading temperature spikes all the time and messing up PW (it was Audi siingle pole unit), with a Bosch sensor from BMW. Measured temperature/resistence pairs for easytherm 5.0 ( -18degC - 15400 ohm; 21 degC - 2200 ohm; 96degC - 183 ohm; also i've got 1k ohm bias resistor ), followed the steps to write files, downloaded to MS (MS1/Extra with V2.2 board), copied ini, but Megatune reads minus 16degC in a cold car with 2degC outside temperature. IAT reads correctly: 2degC.

Gave a shot with Tuner studio. Copied .inc files to project, turned on Tuner studio ant it reads 2 degC IAT and 26degC CLT.

Tried to start car and drive a bit for datalogs. Haven't got any CLT spikes, car now drives good, but CLT readings are way off.

So can someone tell my what i'm doing wrong? Hope You understood me.

Is there a reason you're using a 1k bias resistor? Your measurements suggest the sensor is standard GM which is ok with the default 2490 ohm one.
BTW, Tuner Studio has a much easier to use thermistor calculator. It gives you a choice of 'stock' ones - or you can enter your own values.

1k bias resistor left from my previous setup, because it was reading 96degC all the time and i wanted a bit more resolution in the high temp range.

Doesn't the thermistor calculator in Tuner studio only work with MS2? Or i'm missing something here?

Maybe it has something to do with ground wiring for CLT sensor? I've grounded it to TPS ground . Didn't have the time to try different ground spot, my car is at home and i'm studying in other city.

Something very odd if you had a similar problem before.
My original EFI maker's wiring used separate ground wires for each sensor - same as shown in MS wiring diagrams. So I simply followed that.

I've made my wiring by myself, but followed all suggestions from MS manuals.

I didn't have such a problem before. With previous CLT sensor i recalibrated my MS and Megatune for it and Megatune was reading temperatures right. I've changed from single pole sensor to double pole because of spikes in readings, single pole sensor is grounded to the engine head.

I've not know any sensor which grounds via the engine block used for injection - but they were common for temperature gauges. I'd say you'd have the same problems as sharing any sensor ground with high current ones.

I know single wire coolant sensors were used on aircooled l-jet and d-jet systems.

You're correct, it was sender for temp gauge. Those where on many 80-90' VAG cars.

Ok, so lets get back to my current setup: two wire sensor grounded to TPS ground. TPS ground is not a high current ground, i doubt, that it'll make a difference, if i reground it directly to MS (TPS ground goes straight to MS ).

I'll repeat myself here: Megatune shows -16degC and Tuner studio shows 26degC, with real temperature being 2degC. inc. files for Megatune and Tuner studio are in the right locations.
Why Megatune and Tuner studio are showing different readings and why those readings are wrong? Any suggestions?
I'm sorry if i'm badly explaining the situation.

Megatune is unsupported.

You might get some support if you start a new topic in the TunerStudio sub-forum.

James

Thank You, James.

PauliusNORCO wrote:You're correct, it was sender for temp gauge. Those where on many 80-90' VAG cars.

Ok, so lets get back to my current setup: two wire sensor grounded to TPS ground. TPS ground is not a high current ground, i doubt, that it'll make a difference, if i reground it directly to MS (TPS ground goes straight to MS ).

I'll repeat myself here: Megatune shows -16degC and Tuner studio shows 26degC, with real temperature being 2degC. inc. files for Megatune and Tuner studio are in the right locations.
Why Megatune and Tuner studio are showing different readings and why those readings are wrong? Any suggestions?
I'm sorry if i'm badly explaining the situation.

I'd ignore MegaTune and concentrate on TS. I'd first change the bias resistor back to standard since you're now using a standard(GM) sensor. Change the thermistor settings in TS and see if it now reads ambient OK. A quick test is to substitute the sensor for a 2k5 (1k0 +1k5) resistor. TS should read 20C.