Originally Posted by LVR

It's detonation.... cause unknown as yet. It is NOT normal, and is a prelude to pre-ignition which means $$$$$$$$$$$$$$$$$$$$$ It can occur for a very long time before you get to that and in some cars can never get any worse. My 4.8 goes in to have the engine opened up in 2 weeks time.

Generally it occurs when the engine is warm from having been driven around town. It can be replicated by light throttle on an uphill incline which puts the engine under load but not enough to cause the trans to kick down.

That means when you are driving any road with a slight incline you have to force it to kick down to avoid the detonation. Not good.

I have had 4 software attempts at fixing it, have driven for 10 months with nothing but BP Premium 98 (as it has a detergent) and been told that this engine cannot have carbon build up.

The inlet manifold is coming off and an internal examination of valves, combustion chamber and cylinder walls together with a compression test is next.

Will let you know what happens........

Cheers Vin