Diesel Injectors

[fbs1000]

Morning all hope everyone is well.

Yesterday I had my car serviced ( Rover 75 conni with the BMW engine ) The mechanic told me he thought it was running a little rough and did the following :-

Engine running and pulled off each plug to the diesel injector ( I guess he means the power ? ) the car started to judder when he pulled out 1 , 2 and 4 however when he pulled out 3 it made no difference to the car at all. Does this mean I need a new injector ( common cause ) or could it be one of the following :-

1:- Firing out of sync
2:- no power going to the electric bit on top.

I have manage to locate 2 x diesel injector for the grand old price of £30 delivered, yes you read correctly £30. But would it be wise to attach it to a T4 first to make sure everything is ok with the power side and it's not firing out of sync. Also can you remove the pwer bit whilst the car is running , is this advisable?.

Many thanks again all and I hope each and everyone of you have a great weekend.

Richard