ECU

Back in 2014 I had just bought a 1955 split screen camper. It had the usual 1584cc twin port engine fitted with a 34PICT carburettor. I’d swapped the 009 distributor to a vacuum advance one but I couldn’t get rid of an annoying flat spot just off idle. After spending many hours swapping carburettor jets and fiddling around with different distributor setup I came to the conclusion that the only way to get the engine to run as I wanted was to replace the carburettor with a fuel injection system.

I started looking for an ECU I could use on my VW from another vehicle. ECU’s fitted to modern cars are very complex, they don’t just run the engine, they control the door systems, the lights, some are linked to one key. Motorbike ECU’s are much simpler and I found some software that I could use to re-map Triumph parts.I I bought a couple of ECU’s originally fitted to 4 cylinder 600cc Triumph and two sets of throttle bodies from a 3 cylinder triumph. The throttle bodies were the only ones I could find that were bolted directly to the cylinder heads, most were attached via rubber tubes.

I got this setup running on a spare 1600cc engine pretty quickly but I came across some issues


  • The centre pull linkage I was using wouldn’t stay in adjustment. I would set it up with the engine cold and that would work fine to get it started once the engine was warm the linkage would go out of adjustment. If the engine stopped it was difficult to then get it re-started.
  • Although I could remap the ECU there were lost of variables that were fixed. The Triumph motorbike idled at 1500 RPM so this was the lowest RPM point in the tuning table. The highest RPM column in the table was at 12000 RPM, not much use to anyone with an aircooled VW engine. The amount of fuel injected at startup was fixed for the bike, it was so far off that it could sometimes take 20 minutes just to get the engine started.
  • Although I could re-programme the maps the software didn’t allow me to change them whilst the engine was running. Each time I wanted to change the fuel or ignition map I had to stop the engine, download the current map, make the changes I wanted, upload the map then I could start the engine again. Each cycle took 3-4 minutes so this quickly became very tedious.


I started looking for an alternative ECU, there are lots of aftermarket units on the market but most of them cost in the region of £800 to £1000. I regularly drive my camper onto the continent maybe I’m being over-cautious but I wanted to be able to carry a spare unit, I didn’t want to find myself stranded with a damaged ECU in the middle of Germany, it’s not like I can call VW for a replacement. I couldn’t have the better part of £1000 tied up in an ECU I might never use.

I’d been watching with interest the development of something called ‘Megasquirt’. Some guys in the US had decided to design their own ECU presumably because they also found the aftermarket stuff too expensive or unsuitable for their applications. They went from a relatively simple plug in processor to something they called Megasquirt 2 then Megasquirt 3. Megasquirt 3 was the one that interested me, finally they’d developed something that could drive multiple injectors and coils as well as control peripherals like an idle speed control valve. Unfortunately they continued to use their original control board with the same old power supply and input circuits. The Megasquirt 3 add-on board was connected to the base board via 3 IC sockets, each with 68 connections. As a designer of high-reliability electronics this didn’t seem like the right way to go about it.

I bought myself a Megasquirt 3 daughter board and set about designing my own ECU around it. My ECU is all on one printed circuit board designed to fit into a sealed enclosure using sealed automotive connectors. This is the circuit board you can see on the home page of 1584 Engineering. Finally had the basis of a reliable and economically priced Engine Control Unit. This would be the basis for my fuel injection system.

The specification of my ECU is as follows

  • 4 independent injector drivers. Each one protected against short-circuit.
  • 8 logic level ignition drivers, designed to drive a Bosch coil.
  • 2 crank / cam sensor inputs. Designed to connect to VR (Variable Reluctance) sensors
  • 2 outputs capable of driving stepper-motor, idle speed control valves
  • 8 analogue inputs to enable monitoring of standard automotive sensors temperature, pressure, wide-band lambda, throttle position etc.
  • 1 output capable of delivering up to 10 Amps to a fuel pump (transistor controlled)
  • 1 output to drive a tachometer.
  • Switched mode power supplies to generate internal voltage rails for processor, analogue circuits etc.
  • Sealed automotive connectors & enclosure to give the best possible electrical connection
  • Bluetooth module to enable wireless connectivity to any windows based laptop. This is purely for the purposes of programming and not required fo the engine to run.
  • A programming laptop should run Megatune, Megasquirt’s programming tool. Megatune Lite is available for free and has all the features required for programming the ECU.