Audi A2, 1.4 Tdi ( 3 cylinder engine ).
Customer was informed by third party that the ECU was at fault, read on below to reveal our findings:

Vehicle is driving and idling rough, also lacking in power.
Global serial scan carried out. Various fault codes found including:
P1668 – Valve for pump / injector cylinder 3 – N242 electrical malfunction in circuit.

Fault codes cleared and live measuring blocks logged whilst engine is idling.
Fuel quantity per stroke measured, no deviation on cylinder 3.

Storage scope used to measure the following for each injector:
Injector current, injector live switching, injector earth circuit, multi-pulsing phase,
injector duration, injectors electromagnetic winding’s.

See pictures above showing injector 1 & 2 voltage and current being measure on the scope.
Injector three testing reveal no voltage or current present.

Rocker cover removed and injector loom removed and bench tested. Loom ok.
High pressure camshaft and drive train inspected and ok.
Injector on cylinder 3 faulty and needs replacing.

Vehicle also requires a set of glow plugs. Resistance as follows:
Cyl 1:- 1.4M ohm / Cyl 2:- 1.3 ohm / Cyl 3:- 5.0K ohm.