If the wiring was open circuit or the injector open circuit then an open circuit fault would be logged.
A cyclinder misfire is detected when the crankshaft doesn't accelerate as expected after the injector is fired, which suggests that the injector is faulty.

PS The left inlet tracts being oilier is because the EGR tube is in the left side of the air intake.

To test the injector in cylinder 6, I switched it with the one in cylinder 7. Still, I received fault code P0306, “misfire detected in cylinder 6”. How strange, I thought.

A friend then suggested that the fault code in fact is indicating a misfire in the 6th position of the cylinders’ firing order: that being cylinder 3 on the TDV8 4.4 engine. Accordingly, I switched that cylinder’s injector with the one now in cylinder 7. However, P0306 still appears, along with a rough idle, fluctuating RPM and a smell of unburned fuel.

I have also checked for continuity on the wires going to the injector in cylinder 6 from the ECM. No apparent issues there.

Is there another way I can test the injectors’ harnesses for short circuits?

Save for doing a cylinder compression test, what other steps could I explore?

Update -

I have not yet tested the cylinders’ compressions, but I have disconnected the injectors’ wiring harnesses and cranked the engine, listening to each cylinder. The engine sounds uneven - like one of the cylinders is only softly compressing.

To make matters worse, I have discovered what looks like oil in the coolant header tank and possibly coolant in the engine’s oil.

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Oil in the coolant and vice versa is normally caused by the oil cooler leaking….. that is, provided you have no other issues….

Hopefully you will get a full diagnosis soon then.

 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

On the last pic, on the earlier post the small pipe is supposed to be attached to the inlet pipe, it looks to have snapped the fitting off, there is a thread on how to fix that with some threaded parts. The gunk looks like it’s been glued back on. There is nothing that can't be fixed with a hammer😜😜
FFRR 4.4 SDV8 Autobiography Santorini Black.
Fiat 500x 1.4 multiair Lounge 2015
2010 LR D4 Commercial 2.7 TDV6

mjdronfield - I really hope that’s the case and it’s not something more… catastrophic. But the oil cooler was replaced earlier last year because it was leaking oil down the back of the engine.

northernmoneyjones, I actually have since replaced the entire coolant pipe. Better safe than sorry. 👍

So far, I’ve:

1) block tested the engine twice (no exhaust gases in coolant system = no head gasket failure, no combustion leak),
2) tested all glow plugs (all working), and
3) compression tested all cylinders.

Compression test results (psi):

Cyl1: 355
Cyl2: 380
Cyl3: 378
Cyl4: 362
Cyl5: 385
Cyl6: 100 (wet - 4ml oil: 105)
Cyl7: 385
Cyl8: 380

Would all the above indicate:

1) cyl6 piston rings are working ok, and
2) a potential issue with the cyl6 valves?

If it is a valve leak, would it likely be the valve stem seal that needs replacing or the valve itself? If the former, how easy/possible is it to change without removing the head?

Recommendation for a place to buy valve cover alignment tool (JLR-303-1244)?

Valve stem seals are only oil seals. Unfortunately I don’t see any choice but to remove the head - you have been very unlucky. 2012 TDV8 Vogue (L322)

A failed valve stem seal can't cause low compression.

Considering the ticking noise I wonder if a failed rocker / lash adjuster is causing a valve to be barely opened or perhaps not at all. Replacing a lash adjuster isn't a head-off task, only the valve cover / inlet manifold and camshaft.
Part# 1336545

Wouldn’t a valve rocker fail safe ie closed ? 2012 TDV8 Vogue (L322)

If the lash adjuster isn't sealing properly then the adjuster piston won't push the rocker to open the valve. Same operation as a hydraulic lifter for OHV engines.
Edit - not well stated, as the lash adjuster holds 1 end of the rocker while the camshaft lobe presses on the centre of the rocker to force the valve stem down.

The strong diesel smell out the exhaust suggests that the inlet valve isn't opening, if the issue is indeed caused by a failed lash adjuster. The inlet camshaft is the chain driven camshaft which adds complexity to the repair, but perhaps only need to remove all the camshaft bearing caps to lift the rear of the camshaft enough to lift out the failed rocker assembly.

But if the valve stays shut this won’t cause compression loss. 2012 TDV8 Vogue (L322)

Yes it will as the inlet air is required to be compressed. If no air coming in then a partial vacuum will be created as the piston goes down.

Makes sense. I assume these are 4 valve heads so are the rocker’s acting independently ? 2012 TDV8 Vogue (L322)

Yes they will be operating independently as 32 are used in the engine and they're the same as used in the 2.7, 3.0 and 3.6 engines, which then casts doubt on the theory. For both to fail there would need to be a blockage in the oil supply to both, which is starting to stretch the idea.