I'm not sure what problem I may have caused but what has happened is....
I am running a single turbo and I thought I'll upgrade injectors to 850/1600 (has been a mission to get it to run, let alone properly) and while I was doing that I decided to remove the ratsnest, as soon I did that the exhaust over heat warning light came on all the time, so I decided to put it all back in to see if I could stop it from happening and it did, but now when I hit any where from 2500rpm to 4500rpm the light flashes ramdomly - too fast for me to count the flashes.

I thought I'd try and pull the codes from the computer(PFC) but there are none.

Any ideas on what might be wrong, could it be my o2 sensor? how do you check if they are ok?

or could it be the new injector setup causing?