Looking for advice - 964 ECU damage after welding?

[Johnny Graham]

Hi folks. Just finished putting a cat bypass/new lambda sensor on my 964, also replaced the ratty old magnesium lower valve covers whilst I was at it.
I had to fabricate new corners on the cat inlet flange, as it all crumbled when I split it from the old cat - so 4 little MIG welds essentially. I disconnected the battery as you are meant to do - and thought that this would mean that all the electrics were safe. My earth clamp was on the flange right next to where I was working.

So, it now won't start, just turns over and tries but coughs and pops - and I cant think of anything else that should cause that other than a fried DME/ECU. Different DME relay doesnt help, fuel pump and dme fuses are good, disconnecting O2 sensor doesnt help.

I'm planning to send it away for test tommorrow- this place sounds OK.
http://www.the-ecu-doctor.co.uk/

Bummer! Another day at school, eh?

Anyone got any thoughts?