Weird 2.2 20VT failure - melted piston

[afen]

Earlier this year I melted a piston in my engine, and I really wonder how it happened, as the engine worked fine until the breakdown. I was in 6th gear, doing about 60km/h when I stamped the loud pedal. The boost came and the engine went kaboom.

I took the piston to a local engine builder with 20 years experience when it comes to these engines, but he could not offer an explanation, he had not seen this type of failure before. The only theory he had was that the injector somehow got stuck in open position and dumped gas on the piston.

There's no indication of the engine running lean, and all the other cylinders were ok.

Here's a couple of pictures:

[K Simmonds]

That is odd and a real bummer . I've never seen anything quite like that before!

An injector fault could be the cause, maybe it jammed or a in a position which allowed that cylinder to briefly run very lean? Or dump fuel in constantly as the chap you consulted suggested.

I'd definitely get the injectors serviced/flow checked.

I'd also closely check the condition of the injector connectors, the pink insert goes brittle and can cause poor contacts however this normally simply results in a misfire.

Can't really see it being an ignition system fault, though I guess it would be good to check it everything over thoroughly to rule it out.

Anyway you have my commiserations Hope you can find out what cause it!

Is the block badly damaged?

[PRY4SNO]

How do the valves look?

[sam80quattro]

I have a piston on the shelf with very similar wounds.. Came out of a 150bhp 1.8t engine that was fitted to an s3 with a remapped Ecu for the original 225 motor. It also burnt a valve. I thought it was a mixture of wrong compression ratio and running lean..

[JP]

intake manifold airleak combined with worn exh guides and poor sealing valves. See it all the time. Cylinder temps go through the roof and melt the pistons and burn exhaust valves/seats.

[adam g]

I've melted one due to running lean at high boost.

[newsh]

I've melted one due to running lean at high boost.

+1 ^^ Me too! On a 10v with a dodgy fuel pressure reg, looked similar to that, and the car was absolutely flying when it went

[afen]

The head has no signs of damage, I could probably just reuse it, but I sent it to the engine builder as well, just to be sure.

I've had an engine blow up due to running lean before, but it had the classic craters from running lean. I also had a wideband O2 sensor plus EGT gauge on the car, and they both showed normal values before the engine blew up.

The engine builder noticed something weird with the head, the valve seats/valves were seated very high in the head, needing a couple of mm of lifter rise before creating somewhat of a gap. Some valve guides were also replaced, but not all.

I bought a new block, rods and pistons. I can probably bore the old block and reuse it sometime, but used 81mm pistons are a lot cheaper than new 81,50mm pistons.

I'm also getting a new set of green giants and a remap of the ECU, just to be safe.