need to open it to put fuel in! Its thirsty!

get about 500klms before i need to fuel up, around 11ltrs/100klms

No, it wont.

changing oil will not do a single thing for fuel economy unless you go thinner oil or the oil in there is past it's used by date and full of dirt. Even then itll make very little difference.

Protecting the engine with good oil yes, but unless its thick with contaminants, it wont make a noticable difference to fuel economy.

Nothing on an AMG is synced for fuel economy, it is all for performance, fuel economy takes a back seat.

Vacuum leaks generally make the engine run lean more so that rich, for two reasons, 1 is more air is entering than the MAF reads, 2 is less manifold absolute vacuum means marginally less fuel will be sprayed from the injectors, as the fuel pressure is near constant, the vacuum is less, meaning the difference in pressure between injector inlet and outlet is less, less fuel will flow, even if only extremely slightly. The higher the vacuum in the manifold the easier the flow will flow from the injectors.

The O2 sensors will see the lean mix and attempt correction by increasing injector open time, however they generally wont push it to a rich mixture so much so that you will go through excessive fuel.

Ive been filling up with 95 octane fuel instead of 98 lately and it seems as though it runs better on that.

No idea why that would be.

found the issue, right bank was running lean and correction was maxed out, left bank was running ok but had been adding significant amount of fuel around lower RPM and higher vacuum situations.

Injector seals were all completely buggered, most of them fell apart while pulling them off. They were new with the injectors, so they were obviously very cheap rubish they put on.

all 16 seals replaced and then after driving 15klms to service shop it had improved, but now had codes for being very rich.

After being reset it ran very well, and has not set any codes since then.

The seals were obviously allowing alot of air past them and causing the lean mix, especially on the right bank.

Power has improved at part throttle significantly, and itll now spin the wheels in 2nd gear taking off when i drive in winter mode, which it was flat out doing if i floored it to kick back to first before.

Im looking to get a wavetrac, this open diff is a joke in this car.

no worries mate, with all id replaced, there wasnt much left. I never even looked at injector seals because they were new when i got the injectors.

yes theyre all 18 months old and still fine. I replaced the whole manifold with a new one, and it had new rubber caps.

i got them from an injector service centre over here.

My advice to a lot of you guys is to change and install new coil packs. No one should still have 18 to 20 year old coil packs on their car like I did. This plus plug and spark plug wire change has made a world of a difference with the idle,power and fuel economy. Feels like a brand new car. Especially power and idle wise. Also if you know how change your valve cover gaskets and reseal your valve cover breathers. Change all vacuum lines as well. These things as well make a difference.

i did all that, i had someone else do my breathers and the barstards leaked after 6 weeks, so i did them myself, no more leaks...

I replaced the leads with a factory genuine set, which was perfect, included 16 correct leads.