[Piwoslaw]

Originally Posted by amnonholland

I would run water injectors off the spark ignition signal.
[...]
Could a diesel injector be used and a diesel pump?

Why do you need spark plugs in the first place? As mentioned earier, you'll need a diesel block, since it's stronger, so why not use the diesel cycle in the fuel side to begin with, and use the injector signal? Or instead of injector signals use two injector pumps, one for fuel and one for water, and you can adjust the timing of the second pump. The only downside is that diesels are more efficient, so the exhaust will be slightly cooler, but I think it'll still be more efficient than converting a gasser.

Originally Posted by amnonholland

Also the engine wouldn't run as smooth because of the different expansion rates and torques created by the steam pistons as opposed to the fuel pistons.

Use an 8 cylinder diesel in such a way that there is always a pair of cylinders in the same phase. One cylinder in each pair would be fuel fired, the other water.