CRDI 2010 Black Smoke By Escape

I continue with the problem, I change clutch switch and do not pass the car to scan and do not throw any anomaly with which the mechanic tells me that it must be failing injector which, as they contest them in the bank, indicate the mechanic on the MAF sensor, he told me that if the scanner was bad, the only change was noticeable in the car. A spark plug and then shoot in force but made the cloud of smoke when making short change, but if the forces emits a new cloud of smoke it takes speed and is low to the minimum. I will appreciate help to decide to change injectors which cost a lot of money.
Auto does not consume oil or increased diesel consumption
thanking in advance.
José

Good colleague could put a mark and line of the car, so I could help you a little more