2004 Mk1 Focus tdci Random misfire
 

I've recently acquired a 2004 MK1 1.8 tdci with 129K on the clock. Ran perfectly on the test drive but after the 15 mile drive home the engine began cutting out, so both the Cam and Crank sensors were changed for the modified Grey versions. This cured the problem immediately, but since then it has misbehaved to the point where i want to reach for petrol and matches.
1. FUEL INJECTORS.
After further problems with non starting i paid for a diagnostic on a Delphi live analyzer which showed cylinder 1 not delivering any fuel (DTC P200). However after switching the ignition off/on, the live graph showed Cylinder 1 now delivering fuel the value shown on the graph i remember was about 600-650. But this time Cylinder 2 was now not delivering any fuel. This non fuel delivery continued to alternate between aforementioned cyliders. This was happening with the engine on start up and later at operating temperature. 2 Reconditioned injectors were purchased from a seller on Ebay. After fitting these the starting problems have gone, but during installation the mechanic pointed to a clicking sound coming from the EGR valve, which we ignored whilst installing the injector and clearing the fault code.

2. THE ECU.
Now the all fault codes are gone but the live graph is now showing Cylinder 4 not firing at all and the engine misfirng at all temperatures and difficult to drive on just 3 cyl's.
Having spent so much i asked the mechanic to check the ECU which is located in the drivers side kick panel. It was found to be a rebuilt unit with all connectors in good condition.

3. FINAL DIAGNOSTIC.
The software then asked to carry out a overall electronic test of the ECU.
It asked that :
1. All 4 doors be left opened.
2. Rear wiper left on.
3. Hazard warning on.
4. Ignition on. - Start test.
This showed no faults either. So i'm left with an engine randomly misfiring on various cylinders and a clicking EGR valve as a possible direct cause. Any pointers?