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BMW E30 Megasquirt & Wasted Spark ECU Convertion
This is a guide to upgrade the Motronic ECU fitted to BMW's E30 3-Series (1988 to 1991) using the after market ECU Megasquirt, and a Coil Pack for Wasted Spark. The model used in this guide, is a UK spec 1989 325i. Other models may very, particularly those models that use the pre-88 Jetronic system, which will require additional work.

Parts Needed
Megasquirt I or II Megasquirt connector & short Wiring loom Coil Pack (Vauxhall Vectra/Omega V6) Wideband O2 sensor (Innovate LC-1) Motronic Plug (scrap ECU box) TPS (Throttle Position Sensor) IAT (Intake Air Temperature sensor) Hose Wire Diodes

Megasquirt ECU
Megasquirt can be purchased in kit form or ready built. Either way, you need to order it with two additional spark outputs. See the main Megasquirt site for suppliers and constructional details. For details on wiring the additional coil drivers, see this page

Wiring the ECU loom
Wiring Megasquirt to the car, can either be done by connecting every component directly (sensors, injectors, coil etc), or reusing as much as the existing wiring as possible. In this guide, we do the latter, by gutting an old Motronic ECU box, and reusing the connector. Additional wiring will be needed for the coil outputs, and the O2 sensor. The Megasquirt box can be bolted on top of the Motronic case, or if your building MS in kit form, it's possible to put the MS circuit board into the old Motronic box.

Wiring the Coil Pack
The coil pack used, was a Vauxhall Vectra/Omega V6. It has 3 coils with 6 outputs. Spark plugs are fired in pairs, on the ignition and exhaust stroke. The M20 firing order is 1-5-3-6-2-4. The three Megasquirt outputs are A B & C

Bank A = Cylinder 1 & 6 Bank B = Cylinder 5 & 2 Bank C = Cylinder 3 & 4

Coil Pack Plug: 1 (A) Cyl 1 6 (nearest to 4 pin connector) (My Brown) 2 (B) Cyl 5 2 (My Yellow) 3 (C) Cyl 3 4 (my Blue) 4 +12v

It's more convenient to install the coil pack closest to the bulkhead, so you need to reverse the plug leads so that the shortest is at the back, longest at the front. I found a coil pack plug at a scrapyard, and used shielded 4-core cable from CPC Part:CB08732 to connect directly to Megasquirt.

Wideband O2 Sensor
Ideally the wideband sensor needs welding into a section of the exhaust pipe that sees exhaust gases from all six cylinders. This may not be practical, without using two sensors. However, you can compromise, by just sensing the gases from 3 cylinders, and assume the other 3 cylinders are the same. This is not ideal, but better than doing without.

There are 3 relays next to the expansion tank (one may be missing). One of these (the missing one!) controls the O2 sensor (if fitted). The connector for this, is under the battery tray, and can be used to power the Wideband sensor. Cut off the connector (or find a suitable plug), and use the green & white wire. The Innovate LC-1 controller requires two separate earthing points. Attach one to the body of the car, and feed the other one through the bulkhead to to the Motronic connector along with the output wires. You need to use Output 2 (brown) as this is confirured from factory for wideband use.