The Main Relay starts the fuel pump but if you don't have the ECU grounded at the thermostat housing that may be a cause. The ECU takes over after the prime starts. I know of a complete write up on how that system works on my Mini site somewhere but would take a while to find. Actually found it very quickly by paging back about 4 pages in one particular problem thread. JS
Lots of good stuff above.
And yeah, the 'twinkie' is only OBD0, OBD1 and beyond dont use this.
Going back to the main relay option... while its doing the fuel pump side of things correctly, it does tell the ECU to do things too.
It for one supplies power to the ECU. Have you confirmed there is 12V on both of the ECU power pins, and ground on both too? +12V is A25 and B1 (using normal OBD1 counting, not your crazy diagram counting
), and ground is A23 and A24. You should also check that D1 has +12V also, and this is a constant power (not ignition switched). D1 is the ECU Voltage Backup pin.
B9 is powered via the Main Relay when you crank the engine, it tells the ECU when your cranking, and to start injectors, fire the spark etc... might want to check that this isnt intermittant...
A7 is grounded internally to the ECU when you prime, and then disconnects (open circuit) when priming is complete. Then when you crank the engine, it will ground internally again and should stay grounded from this point I think. It knows to do this via the B9 pin that you are attempting to crank it etc. I am 99% sure it will ground and then open circuit for priming, and then ground and stay grounded for running, so the pump stays running constantly. Again, something to check...
A21 is the signal that goes to the dizzy to fire the ingitor... you should check that this does goes +12V when you are cranking the engine. You may have done this from the dizzy end already though.
Injectors. These are powered directly on one side, and are grounded via the ECU on the other side. The ECU controls the firing of them by switching the grounded side. The positive side should all be connected together, you may have checked this voltage already - but I think you said its fine and wont effect your spark anway.
Just a few things to ponder..
Edited by strudel, 16 May 2010 - 11:18 PM.