yeah looks like it melted, mine did the same thing on my #1 cylinder

 

Sorry to hear about your problems. How does the bore look when you lower the piston? Is there any material missing on the bore where the damage on the piston is? It's a bad picture, but it looks like there are tiny indentations on the piston as well, not sure if its just the picture though.

 

TJ, was this only on number 4?

 

There are white/gray spots/blobs around the edges of 2 and 3 as well. The same kinda white that you can see around the piston damage in the picture.

 

have you monitored the a/f lately? Sounds like you might of lost fuel pressure

 

Here is a log file from earlier in the day as I upped boost to see what AFR was. For some reason it didn't log knock.

 

The log looks good.

 

I think I figured out how it went lean and blew. I was calculating how much Stabil to throw in the tank when it hit me.

I had just gotten back from a trip and the car was low on gas. My brother's wife was supposed to PCS to England the next day and I promised her a ride. It was supposed to hail in 45 minutes, but was clear at the time. I took her out for a ride on the way to get gas and the gauge just dropped down to 2 bars and I didn't think anything of it. I usually keep it full or at least above half. I'm pretty sure I starved 1 of the Walbros of fuel, it went lean, and pop.

 

Yeah, theres a decent amount of damage. Sleeves 1-3 look and feel like they are brand new and 4 is...

 

this has been gone over b4, but bc of the nature of our intake manifold, cyl 4 will lean out b4 the others, try adding more fuel to cyl 4 next time around, I did this on my last tune