Came to get my new 3 door out today and its running like its on three, its carlos old 500 rep and was running fine when i got it but has only been run in out of the workshop for 2 weeks and did run out of petrol last week, checked plugs all ok, but if you unplug no 1 and 4 injectors it cuts out, 2 and 3 it carries on running, any ideas please??