Hi guys Hoping someone might be able to give me an idea where to start with this... 2003 BA XR6 Turbo, 125000KM. I am the second owner since I got it at 120000KM where it was in stock standard form around 8 months ago. A week after owning it I took it to HorsePower Factory and got a basic custom dyno tune, cold air intake, with the factory fuel injectors and valve springs left alone. All was well for 3000KM and then the gearbox started slipping, so I had the BTR 4 speed rebuilt to OEM spec less than 2000KM ago. When I got it back the car was going great, feeling a lot of responsive and agressive. A few weeks later, it started missing at idle so I swapped the coil packs and spark plugs for new genuine Ford ones. Since then, it idles perfectly, but I now get a loud backfire at wide open throttle when shifting into 2nd. And just now tonight I noticed it is missfiring fairly badly around 50% of the time when WOT from 80kph... sometimes its a short missfire and it clears and keeps pulling hard, othertimes its spluttering really badly so I back off the throttle. Tonight was the first time I had tried WOT from 80KPH since doing the plugs/coils a month ago. Aside from that, it drives great as my daily driver, and sits on 110kph towing my dirtbike trailer no worries. I have checked all the air intake hoses and everything is still in place since I did the plugs and coils. I am wondering if it is something to do with the spark plug gap? In my receipt from HPF it shows "re-gap spark plugs as required"... so perhaps these new OEM ones aren't fitting the tune? Or perhaps I have a faulty coil pack, which would be bad luck as they are brand new. Unfortunately I threw out the old coil packs and plugs. Is it common to modify the spark plug gap when tuning these? Should I just ask HPF to re-gap some new plugs for me? Thanks in advance for any ideas you have, love driving this car and looking forward to sorting this out. Cheers, Tim