AU2 XR8 tooo rich @ WOT

[andoef]

G'day fellas, i've been off the forums for a while as ive been 4wding a fair bit, but as an avid ford fan ive rescently purchased my 4th falcon, an AU2 XR8 Ute...

Anyways, i've come across a strange problem, which would have gone completely un-noticed had i not run it up on the dyno to check the AFR's...

So basically, Mixtures are fantastic, to the leaner side of stoich at idle, cruise and part load, however above 3000 at wide open throttle the mixtures go from 12.5 (expected), fly thru 11, 10 then off the richter, rich alomst instantly.

I suspected the MAF sensor could be responsible for this however backprobing the sensor gave a reading of 4.3v at 4000 rpm full load which seems normal??

The car has 130,000k on the clock and is stock except for a catback. All sensors appear to be opperating normally and no DTC's present..
Strange part is the car goes very well and has no symptoms, so this is pretty unexpected.
I knew another bloke with the same car near by with 200,000 on the clock so we ran his up and the AFR's were very similar...? Perhaps the airflow meters go out of calibration?
Basically, has anyone out there come across this?? Is this just a factory tune to protect the pistons ( hard to believe, as his was blowing alot of unburnt fuel out the pipe which would be unacceptable for a car when new).. Makes you wonder how many other XR's may be out there with the same problem un diagnosed?