renault master 52 plate no power uphill, black smoke etc?

my van went into limp mode, smoking badly. took it to garage (wish i hadn't) they said it was injectors, fitted recon ones, van still same, so they fitted new egr valve, van ran a little better but still had no power going up hills,so they fitted new air flow meter, van is still down on power. Has anyone any suggestions, maybe a sensor or the timing? Regards Paul