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Converting a Motronic ECU Box to Megasquirt - Part 3
From $1
Getting it working
IAT - Intake Air Sensor Ideally, you want to position the sensor as close to the manifold as possible. Not so easy with basic parts. I used a fast acting GM air sensor, mounted in the stock air box. I have also removed the Air Flow Meter (AFM) completely with some hose I found on e-bay. The AFM is redundant, and only adds restriction to the air flow. You can reuse the wires that went into the AFM. If you dont want to cut the plug off, you can always remove the socket from an old AFM, although some models require a fair bit of dismantling. | Plug pin | Wire Colour | Connection | | 1 | Gray/Vio | Temp Sensor | | 2 | Gray/Yel | | | 3 | Gray/White | | | 4 | Gray/Blue | Ground | |  | | CLT - Coolant sensor Since we are using the stock sensor here, it should work without any modification. On the M20 engine, it's the blue coloured sensor (the brown sensor is for the dashboard gauge). These do fail eventually, so it should have been replaced at some time in the vehicles life. If not, consider changing it. As this is a Bosch sensor, and not the standard MS GM sensor, MS will need calibrating for a correct reading. | Temp | Resistance | | -15c | 12002 | | 30c | 1707 | | 100c | 155 | MS2 can be configured inside Megatune. MS1 requires you to modify the firmware and flash it to the processor. At the bottom of this page, you will find ~Bosch.zip which contains the MS1-Extra firmware. Extract this to your hard drive. Open the MS case, and short the boot jumper (left side of processor). Connect the serial cable, and run "Download-Firmware.bat" Follow on screen instructions. | | | TPS - Throttle Body Sensor E30 TPS Plug: | Connector pin | Wire Colour | MS connection | | 1 | Brown-Blue | Signal in | | 2 | Brown | Ground | | 3 | Brown Black | +5v Ref |
If you are unsure of the connections, switch ignition on (MS on), and with a multimeter, look for +5V (or slightly less). Then do a continuity check to find ground. The third wire is signal in. If your using a Bosch TPS with the round multipin connector (0280120404 etc), then connect as follows: Pin 1 -> +5v
Pin 2 -> Ground
Pin 3 -> Signal In
Pin 4 ->
Pin 5 ->
Pin 6 -> | | | Wideband Lambda/O2 Sensor On E30 cars without a catalytic converter, there is a cable & 4 pin round socket underneath the front battery tray (or next to it). | Wire Colour | Connection | | Black | O2 Input | | Yellow | O2 Input Ground | | Brown | Heater Ground | | Green-Blue | Heater power | The heater output is controlled by a relay in the cluster of three near where the AFM is/was. If it's missing, find one that fits. Sensors: JAW. Connect +12 to the Heater power. Ground can be attached to the bodywork. The JAW output needs to be connected to the black wire "O2 input" LC1:
Red - Heater power (green/Blue)
Blue - Heater Ground (brown)
White - Bodywork ground
Brown - O2 Input (black wire)
Green - O2 Ground (yellow)
Yellow - [not used]
Black - Heater Ground Dont forget to calibrate your sensor, as per instructions.
|  | | Wiring the coil pack (Wasted Spark option) 4 pin connector (Bosch/GM/Vauxhall coil packs): | Pin | Function | Cylinder | | 1 | Spark A | 1 & 6 | | 2 | Spark B | 2 & 5 | | 3 | Spark C | 3 & 4 | | 4 | +12V Ignition | | If your unsure of which pin is 1 use a digital multimeter and check the resistance between one of the outer pins, and the other three pins. The resistances should be consistent. If not, test from the other end. +12v can be obtained from the original coil wires. The green one is switched with the ignition. The coil pack should have the cylinder numbers embossed on it. These cylinder numbers are incorrect, and should be connected as follows. | Spark Bank | Number on coil | Correct connection | | A | 5 & 2 | 1 & 6 | | B | 3 & 6 | 2 & 5 | | C | 1 & 4 | 4 & 3 | | 
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my car wont idle and misfiring under 900rpm