Rover V8 Tuner Studio – CTS / ATS Calibration

Tuner Studio

Although I’d had my Rover V8 4.6L running within seconds of turning the key, nothing was calibrated. I therefore used Tuner Studio to look at the current set-up and sensor calibration.

To learn Tuner Studio, I read literally 1,000’s of pages across numerous websites. What was obvious is a Megasquirt is a universal device and no two engines would have identical set-ups. A de-facto standard for a Rover V8 simply doesn’t exist. Although a .msq file for a similar engine would be a head start, it was in no way going to magically solve my problems. In fact, having one could lead to over-looking vital set-up elements.

I recommend reading

I currently have 2 different Megasquirt’s, an MS1 with built in ignition drivers and an MS2 with External Edis8. The MS1 needs easyTherm to calibrate the sensors, but for MS2/3 it’s built into Tuner Studio. For now I’m going with the MS1, but later I might upgrade the MS2 to have built in ignition drivers.

Rover V8 MS1 MsExtra MSQ File

For my MegaSquirt ECU to function correctly, it is essential that the ECU knows a few constants about my Rover V8 P38. These constants include how to decode the RPM signal that MegaSquirt receives from the crank trigger, how to convert resistance values from the temperature sensor into temperature readings, how long the fuel injectors should stay open, and many more variables.

Over the next few weeks I’ll be publishing more calibration data and msq files.

Calibrating Engine Sensors

A MegaSquirt uses a handful of sensors to determine the operating condition of the engine. These sensors include:

These sensors must all be calibrated to read correctly in TunerStudio and provide the correct data to the ECU during engine operation.

NB: During sensor calibration, the MegaSquirt ECU must be powered on and connected to TunerStudio. Do not do burn changes to a running engine!

In order to reprogram the ECU, use a piece of wire to connect the two pins labelled “Boot”. Once these are connected, power on the ECU – you’re now in reprogramming mode.

A list of useful sensor values can be found here:

Coolant Temperature Sensor (CTS)

The CTS is marked 6 below.

As per this page, Rover V8 MegaSquirt P38 4.6 – extraEfi, I was intending on using a FAE 33370. I noticed that although I’d ordered an FAE sensor, a Bosch one had turned up (0 280 130 026).

Seeing as the seller was a reputable Range Rover specialist, I assume they are equivalent. Luckily, Bosch kindly supply a detailed datasheet:

  That saved a lot of time boiling kettles and measuring resistances.

Temperature [°C] Resistance Ω [Ohm]
-40 45,313
-30 26,114
-20 15,462
-10 9,397
0 5,896
10 3,792
20 2,500
30 1,707
40 1,175
50 834
60 596
70 436
80 323
90 243
100 187
110 144
120 113
130 89

Bosch 0280130026

Unlike some sensors, the resistance changes fairly linearly; especially when at working temperature. Which is good.
I’m using 2 different fan switches. 79°C / 88°C (INTERA033866). and 76°C / 86°C (50250). I have an 80°C water thermostat. The chances of me driving this car in icy conditions are very slim and if the engine ever hit 100°C, it’s game over. To me, it makes sense to use calibration figures based on normal starting and running conditions.

Temperature [°C] Resistance Ω [Ohm]
0 5896.00
70 436.00
100 144.00

The datasheet also specifies to use a pull-up resistor between 1 & 3KΩ. The Megasquirt default 2.49KΩ looks perfect.

Bosch 0280130026 resistor

This datasheet agrees with this guys measurements and the Saab 900 Manual:

Tuner Studio CTS calibration instructions

  1. Choose “Calibrate Thermistor Tables” from the “Tools” drops down in the Menu Bar. This will open a dialogue box with several options in it.
  2. Choose “Coolant Temperature Sensor” from the drop-down menu called ”Sensor Table”.
  3. The second drop-down menu gives a choice of several popular temperature sensors. If the temperature sensor used in your build is in this list, simply select it from the list, click “Write to Controller”, and then “Close”.

The ‘Common Sensor Values’ → Saab(Bosch), sensor settings were probably close enough and the bias resistor was right in the ball park, but I decided to do a few tweaks to the resistance values.

If I did ever change the bias resistor, the Megasquirt manual (page 62) states it’s designated R7:

Once all the calibration has been done and the engine is running, I’ll stick a thermocouple into the radiator and double check the CTS readings in Tuner Studio. I do have a gauge built into my radiator cap, so it’ll be interesting to see how accurate that is too.

Temperature Radiator Cap

Inlet Air Temperature (IAT) / Air Temperature Sensor (ATS) Calibration

I was going to use a FAE 33170 sensor but after a couple hours of searching I swapped to a FAE 33220 (page 83) because I couldn’t find any published resistance data.


Alternative part Numbers:
Ford: ATS 04, 1639284, V86HF-12A697-AA,
Alfa Romeo: 60806471, 500309797, 7547976
Fiat: 7547976, AT1009
VAG: 048 906 161 1
Intermotor: 55705
Lancia: 500309797, 60806471, 7547976
Maserati: 470079700
Delphi: TS10219-12B1
FAE: 33220
Fuel Parts: AT1009
Kerr Nelson: EAT007
Lucas: SNB819
Quinton Hazell: XEMS64
Cambiare: VE375086

  • Mini-Timer connector
  • Fast response time
  • High signal level
  • Low cost
  • Resistance @ 25 ºC ≈ 3 kΩ 
  • Accuracy from nominal values = 5% (W/ºC) @ -40 > +125 ºC 
  • Maximum operating voltage = 5 V (series) 
  • Thread = M14 x 1.5 
  • Seal = 19mm Hex 
  • Connector = Mini Timer 2 way
  • Tightening torque = 24 Nm max

FAE33220 ATS04 Sensor

I made up a 70mm steel tube for mine to sit in, with a 14×1.5 threaded insert.

Rover V8 P38 megasquirt

Temperature [°C] Resistance Ω [Ohm]
-40 100950
-30 53100
-20 29120
-10 16600
0 9750
10 5970
20 3750
30 2420
40 1600
50 1080
60 750
70 530
80 380
90 280
100 204
110 153
120 102

FAE33220 Resistance Vs Temperature

The graph is logarithmic which doesn’t make modelling too easy, especially with just 3 co-ordinates.

My inlet ram tube exits straight out the side of bonnet and taking into things such as wind chill and being stuck in heavy traffic, I went for:

Temperature [°C] Resistance Ω [Ohm]
-10 16600
30 2420
100 204

I’m hoping the inlet air temperature never reaches -10°C or 100°C, so I might narrow the band of values.  If the curve was linear I wouldn’t bother.

The closest default setting I could find in Tuner Studio was the ”GM” sensor, but it wasn’t perfect.

Tuner Studio Air Temperature Sensor



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