1988 BMW 320i Motronic


16VT’s involvement: Wired in fully functional Megasquirt ECU in a plug and play fashion; calibrated fuel, spark and idle.

Chassis: stock;

Forced induction: none.

Engine: 2000cc, M20B20 engine code, 12 valve,stock.

Injection: : Port injection, 151cc/min injectors, Motronic wiring harness, 60-2 trigger wheel, VR crank sensor, PWM 3-wire bosch idle valve, Bosch coolant and intake temp sensors, single coil driven by VB921;

Description: The objective of this install was to use the original wiring loom. To do this, an old 55 pin Motronic ECU was cannibalised and turned into an adapter. The MS was installed inside the car, with wires running to the 'ECU' box. All the original sensors and actuators were used, including the air temp sensor integral to the air flow meter.

A v3 PCB was used, with some additions including a TIP122 for PWM idle control, an IRLZ44 for boost control, 3 VB921's for waste-spark capability, and a few BC337 transistors for some 'extras'. The 3-wire ISV of the car was held closed by grounding one of its pins via a 39ohm 50W resistor. No TPS was connected since MAPdot was used, but there are enough wires in the BMW harness to connect a TPS.

Pin configuration:

MS SPARE PIN (6) is freeeeeeee
MS VR- CRANK SENSOR SIGNAL (7) goes to T55/48
MS GROUNDS (8,9,10,11) go to T55/2,T55/14,T55/24
MS SENSOR GROUND (19) goes to T55/19, T55/26, T55/10
MS MAT (20) goes to T55/44
MS CLT (21) goes to T55/45
MS TPS SIGNAL (22) goes to T55/53 (WOT switch, brown/black)
MS O2 SENSOR SIGNAL (23, brown) goes to T55/28
MS VR+ CRANK SENSOR SIGNAL (24)goes to T55/47
MS SPARE PIN (25) goes to drive coil B externally wired
MS TPS Vref (26) goes to T55/52 (idle switch, brown/blue)
MS +12V (28 ) goes to T55/27
MS SPARE PIN (29) goes to T55/6 (to drive cluster tachometer)
MS FIDLE (30) goes to T55/4
MS INJ1 (32,33) goes to T55/16
MS INJ2 (34,35) goes to T55/17
MS coil A control (36) goes to T55/1
MS FUEL PUMP (37) goes to T55/3 (FP relay) and
T55/36 (DME relay) needs to see ground when ignition is turned on, and to do this a relay is wired in using the ignition (T55/27) line and a ground somewhere, the objective being for he relay to ground T55/36 when it is triggered by T55/27.

The 'extras':

Launch control, JS11 - SPR1, pin 3 (yellow)
Shift light CPU10, JS7 - SPR2, pin 4 (white) (can be routed to T55/15 on US spec cars to convert the check engine light into a shift light)
Switchable maps, SPR3, pin 5 (blue)
SPR4, pin 6 is freeeeeeeeeeeee
Coil B IAC1A, pin 25
Coil C IAC1B, pin 27 (green)
Tacho out, JS1 - IAC2A, pin 29
Output2, JS3 - IAC2B, pin 31 (red)

Car idles at 900rpm (~30%DC). An extra ground strap was run from T55/14 to a bolt on the dashboard. This is the same place where the 39ohm 50W resistor was grounded. The other end of the 39ohm resistor was connected to T55/22.

Ideally, injector 2 and injector 5 plugs might want to be swapped so that they inject at the correct time, but this was not done on this install and the engine idles very smoothly. Waste spark has not been implemented yet, but the ouputs work on the stimulator. Boost control output works on the stimulator as well, but has not been used yet. Firmware used was 029q2. MAPdot acceleration enrichment.