Realised I hadn't updated this.

So after some more head scratching and monitoring with the GAP tool; I decided against going down the injector route as I had very minimal misfires (if any sometimes) on the cylinders. If an injector was leaking enough fuel during driving or even after engine off; I'd expect to see some hard starting issues or misfiring.

Anyway to the point, I have had both high pressure fuel pumps (HPFPs) replaced (on 30th March) and the rich running issue has not returned.

I changed the oil myself just after the pumps were done to make sure the oil was fresh. I have been monitoring the fuel trims and the LTFTs are now respectably under the generally agreed +/- 10.
STFTs (though not as important to monitor) are now responding correctly to driving conditions. I've driven to Heathrow & back twice and have covered roughly 400-500 miles since the pumps were done so I am generally confident I can put this issue to bed.
Before I had the pumps changed, I'd change the oil and within 50 or so miles the fuel trims would go negative -31 because of the amount of fuel leaking past the pumps.

So for anyone wondering; these two videos explain beautifully how leaking HPFPs cause rich running.

- This is AJ133 5.0 / 3.0 specific; it runs through the whole fuel system but the important bit is around 9:25.

- VW engine but direct injection the same as a 5.0, so theory still applies.

In short, the oil gets diluted with fuel from the pumps. The oil fumes laden with the fuel gets pulled back into the intake via the PCV breathers and we have the rich running. The ECM sees more fuel than it expected, it can't adjust the injector pulses anymore so the EML comes on with codes P0172/P0175.

For anyone looking at this in the future, use the GAP tool to monitor your high pressure fuel rail when you switch the engine off. The pressure should go UP for at least a few minutes then settle out. Mine was going down near enough straight away pointing to a leaky pump seal - which pump I'll never know, but they are always best replaced in pairs anyway on these engines.

The car is also far keener now than it has been since before the pumps were changed; happy motoring all!

That’s a great result.

Hopefully you’ll enjoy some trouble free motoring for a while now! 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

Sorted... nothing like a well running 5.0 S/C....  Pete
__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
-Click for Project Fatty off roader-