What would cause this!?
 

Melted valves... Two valve heads were sitting on top of the piston melted and disfigured.. These were Supertech valves as well. Motor is an EJ207 with EJ20K heads.

I am pretty sure my o2 is on its way out, reads 0.06v when cold and 0.00v when driving some times..

Anyways... I was trying to diagnose a misfire at 2500~300 and yeah i was planning to buy an o2 sensor that weekend and this just happened...pics tell the story I guess. i am heart broken.

It was appox 2500~3000rpm, light throttle, cruising..2nd or 3rd gear.

Would others agree a faulty o2 sensor the most likely cause? The car is tuned using powerfc.

This thread had the exact same thing happen!

[url=http://www.iwsti.com/forums/2-5-liter-litre-factory-motor/201278-car-died-will-not-turn-3.html]Car died and will not turn on. - Page 3 - Subaru Impreza WRX STI Forums: IWSTI.com[/url]

I need some expert feedback :)

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uuk faulty valves? was it the intake or exhaust valves that failed? looks like it is maybe running far too much boost or too lean

a faulty 02 sensor won't cause that

Its had some hard det going on.

Who tuned the car?

207 with EJ20k heads. Were the pistons standard 207?
I recall Doug saying that that combo has too high a compression ratio and will ping like a bitch. Perhaps this is the results?

2.1 manley stroker pistons.

I can say i suspect the car was tuned with a faulty o2..

regarding EJ207 and Ej20K heads, i am using the correct headgasket as per the compression matrix floating around. I would like Dougs feedback.. i know they do this combo in the US.

I've heard the motor ping once and that was a on a very hot day, many months before.

Knock doesn't exceed 50, boost doesn't go pass 1.5 bar, mostly running 1.3~1.4.

i suspect the motor was leaning out, surely the o2 isnt to blame??

No, its not.

You are either out of fuel flow/pressure or incorrect mapping.

Timing belt didnt break?

no timing belt didn't break, it was 12 teeth off after the motor stalled..

That information in post one would of helped - Russ is on the right path with it.