However, this seems to make no difference. If I just switch on the ignition, I hear the fuel pump prime as normal and then if I connect the USB cable it re-primes again so is obviously still resetting. It doesn't reset if I pull the cable, but it does if I plug it in again.
I can see that pin 51 is being held high if I measure it with my DVM.
I dunno what I've done wrong?