With the throttle cable sorted I turned my attention to installing the manifold pressure sensor piping and a suitable connection on the engine. The Megasquirt is different to most other aftermarket ECU’s in that it uses the inlet pressure to determine the fuelling required instead of the normal method of just using the throttle position.
Having discussed this with Kevin, he had very helpfully pointed out that a route is built into the inlet gasket. The gasket is aluminium with a moulded in rubber seal that traces a route around all four ports and channels back to a single point, between ports 3 and 4. This meant that all I had to do was to drill through the manifold at the correct position and fix a suitable union that I could affix some vacuum hose onto. The fitting was found in a local hydraulics supplier in Basingstoke (where I work) and had a 1/4 NTP tapered thread. I marked the inside face of the manifold by laying the gasket in place (using some bolts to align it properly) and drilled and taped from the outside. I then fitted the union with a good helping of Loctite thread lock hold it in place and to aid the sealing. I ran a length of silicon vacuum tube from the manifold to the engine bay bulkhead and then fitted a through bulkhead union. This allowed me to break the tube and thus to remove the ECU by simply pulling the hose from the inside union – handy during the initial setting up/testing stages.