What exactly were the codes you had reported?.A reader won't say 'Cylinder 1 not firing',it should say something is out of range or open circuit.If it's open circuit then it's likely to be something in the loom,the injectors do give problems but not in the electrical side of things.
Also,if the van is misfiring then (being a diesel) it should belch out white smoke,thats if the injector is working.If theres no smoke then it is another sign that there is a fault with the injector or connection to it.To make 100% sure which one it is,with the van running,disconnect the connector to each injector in turn.You will find that if you disconnect a good injector/cylinder the engine revs will drop,disconnect a bad one and it will have no effect.
It's all very well saying that number 1 is at the flywheel end,but that doesn't always tally up with the ECU fault code you will get depending on what system you are reading it with and which side of the ECU you are reading.You need to do the above check before you change anything incorrectly.
