OK, I have fitted a Focus engine into a Ford Ka.

I tried a test-fire once the engine was in and the engine was running fine with the Ka ECU.

I changed the ECU to the one from the Focus, and I also changed the Transponder as well, but now the engine will not start (even with the Focus key inside the transponder).

It almost starts but doesn't quite kick over like it did before.

Any ideas whats wrong?

P.S - Nothing else has been altered, just swapped the ECU over.

I am stumped!!!! All wires and connections are connected, etc... plenty fuel, battery is fine, etc.