Starting Issues

The only thing I can suggest is check the wiring or pins connecting to modules. Perhaps some contact cleaner on pins. May have a cable short in connection on old style due to vibration. I believe rotax had issue on old style and went to six pin. If fuel is ok than fire is missing. 

Brandan

Please go through my posting starting two weeks ago. I had a similar issues. I listed the things I did prior to sending my Electronic modules to be bench tested, where they bought failed. New ones fixed my problem. You most likely have one that has failed and one that is failing intermittently. 
Have you tried starting on left mag and then right mag? Have you checked for spark?

good luck

Gino Cavicchioli

Don't know what kind of ignition switch you have, key or toggle. Might be going bad. You don't want it grounding while in flight especially both modules. 

IF toggle switches, bypass and see if it starts all the time if you have push botton start.  If all key you can bypass but more difficult. You have to turn fuel valve off for engine to stop after start. Take extra care when modules hot. 

I have the six pin setup but I have yet to try to clean the pins. I have checked all of them for security though and they look good. I have an older key start so I can't start one module at a time. Basically I only installed one module at a time to see which ones weren't working without the influence of the second module. 

Looks like you have answered the problem that although expensive you need new modules. But, this coming back next day, ENGINE starting, and all good is an issue. Well, as another member said one old module working sometimes and after engine start all ok with both old modules after start. 

The only other possibility which I doubt would be a bad key ignition as stated before. If you don't have some kind of back EMF protection either at the starter solenoid or at key ignition like a diod, ultimately spark generated at key ignition would cause it to go bad. 

Starting procedure inside modules and running after start is different as it relates to hardware and software. I know modules are expansive but you might have to bite the bullet.