Firstly - is the S2 ERST metering head the same as the Mk4 XR3i?

Secondly - the problem - the car ran fine in the garage the last year, but was put back on the road, got tax today and then twice it wouldn't start, but eventually it started up and ran just fine.

Got it back to the garage, determined that there was plenty of fuel getting into the metering head, but none coming out to the injectors. So figured it must be the metering head.

With not much to lose, dismantled it and everything seemed ok, but the passages out to the injectors might have been blocked. Reassembled it and replaced on car, now cylinder number 2 was overfuelling ridiculous amounts.

Tried again, dismantled, reassembled and refittied it again and now both 3 and 4 are overfuelling like crazy.

Any ideas before I try to find a new metering head?