Megasquirt on my SM IE

For carburetted SMs, ignition control could be the way to go. It's a little work to sort it all out, but it could give you better drivability and economy.

I "only" have a carburator engine, but this looks and sounds really interesting to me, thanks for the description!

m.

I am running Megasquirt on my 1973 SM IE, and since there has been some mention of Megasquirt, I thought I should describe my current setup.

I'm using the stock harness/injectors/sensors on this car, in order to keep it stock looking and to be able to revert to original.

The stock setup does not have a manifold referenced fuel pressure regulator, so I replaced it with a VW vanagon FPR. This is optional, and the system should work just fine with the original FPR. There's no proper throttle position sensor either, so I went with a BMW e34 M20 automatic TPS. Bolts right on and works like a charm.

A 36-1 trigger wheel has been mounted to the auxiliary shaft (cam speed). The VR sensor is fairly standard, and came out of a BX GTi. The firmware is set up to trigger the two stock coils, so the RPM counter works as normal.

D-Jetronic switches 12V over the injectors, while Megasquirt switches the ground (this is the standard method nowadays). I solved this by fashioning a rewiring harness to go in between the engine and the stock harness.

Some illustrational details about the changes:



Description:

1. Idle valve (3 pin Bosch valve from a Volvo)
2. Disconnected cold start air valve
3. Spliced into the stock wiring harness
4. Bosch throttle position sensor
5. Disconnected cold start injector
6. Disconnected the idle overrun circuit
7. VW Vanagon fuel pressure regulator (not strictly needed)
8. Removed manifold pressure sensor and routed vacuum hose through firewall
9. 36-1 trigger wheel

I removed the auxiliary throttles as well, since they don't really do anything useful. The coils are new red Bosch coils, ballast resistors are no longer needed, since the MS fires them directly.

I've welded an O2 sensor bung into the exhaust pipe, and installed a Bosch LSU 7057 wideband lambda sensor and a Tech Edge 2E0 wideband unit.



In order to use the original harness, I purchased a D-Jetronic ECU from a Volvo 262 on eBay. I gutted it, but kept the connector and injector resistors and soldered in a connector for the Megasquirt.



1. Gutted D-Jetronic box with Megasquirt ECU
2. Tech Edge 2E0 wideband lambda controller

All in all, the engine runs very well. The ignition control is a considerable improvement over the stock setup. Torque is much better at low throttle openings, so I can easily drive the car at around 1800 RPMS in town. I haven't recorded fuel consumption, so I can't really say anything about economy at the moment.