6A12T high revs power loss

[Lewis]

I have owned my 1996 Eterna for only about a month
It has the 6A12T engine and has an aftermarket exhaust (2.5" whole way) and a gracer air filter. Has 123,000km on clock.
The car runs great most of the time but above sortof 5000rpm it gets all jerky and seems to suffer a large power loss.
A friend used to own a Libero GT, and said he has same probs and it was a bad spark plug lead, it was dropping a cylinder. Im no mechanic but its funny how our problems seem the same and only happen at high revs. I would think that if it was a spark plug lead it would either work or not work.
I have very recently had the cambelt and engine oil changed.
Sadly it is an automatic, but i dont think this problem is to do with the transmission.
I know high octane gas is recommended (highest here is 98 or 96) but i using 91 dosent seem to make a difference to this high revs power loss, even after d/c battery (ive been told that resets the ecu).
Please help if you can,
Thanks in advance

[-LegnumVR4-]

Spark plug gap by the sounds of it, too large. AKO on here can point u in the right direction as he knows them inside and out :embarasse

[ako]

Sounds definately ignition related at least.. Misfiring is a REALLY common problem with these things too. Like rhys just said, try re-gapping the spark plugs (taking off the manifold is 10X easier than it looks, just keep undoing bolts till it moves) and see if it helps matters. Its an easy job, just use a feeler gauge and tap the pugs down to .7mm between the electrode and the stalky bit :p

IF that helps matters, it at least pointed you in the right direction. All 3 TT VR4's I've had have all benifitted from me doing this to them, even when there wasn't a noticable issue. Other things.. Try leads, also the ignition module gives up at times, but thats heat rather than rev related.

Hope that helps :)