Am i going to get any usefull info out of diagnostic mode in my ef with the megasquirt running the fuel and spark side of things.?
Or am i going to be hammered with error code's all the time?

I'll try tomorrow & see what happens then

i was wondering that myself today, let us know how ya go.

There is a good chance you will only get garbage, but it depends on quite a few things.

What diag information is relevant if your engine is running off the MS anyhow ?

Can you elaborate?

The EEC with throw error codes if the sensor data it receives is way off from what it would expect for what IT is doing. Assuming you have disconnected the EEC outputs and share the inputs with the MS2, the EEC will be thinking it is in control but seeing the results of what the MS2 is doing. If the MS2 is running the engine very close to how the EEC would ideally like it to be run, then it will be relatively happy. If it is not happy with the sensor data it is getting, it will try to change things thinking it is still in control, at some point it will realise that something is going wrong and it will start throwing error codes.

So when you run diagnostics, if you get an error code there may be no error, and if you dont get an error it doesnt necessarily mean that nothing is wrong either.

As said ^^^, what information are you after when you run diag?

gearbox,aircon,abs, anything non engine really