Help!

I have a 99 V impreza turbo 2000 uk car. It has 62000 miles full subaru history. It has a K&N induction kit which was fitted at 30000 miles and has a magnex 6x9 oval cat back system also on since 30000. It has a GGR DV and always run on Super unleaded or optimax. Last week the engine developed a knocking noise from the botttom end and subaru have said its the 2nd piston starting to melt and its damaged the bore therfore needs a short motor.
Please can anyone with technical knowledge tell me what could of caused this to happen. The car is hardly ever driven hard always warmed uo and down and i have had it as it stands for 12,000 miles
thanks
Scott

 

its a common problem with 99my cars when they / you fit a new engine get the ecu rewrighten this will stop it happening again any subaru dealer will be aware of this or at least should be

 

you could have a MAF (mass air flow) sensor fault on the car that doesn't show up on the test equipment.

its a very common fault with the v5/v6 cars.

that would be the first thing i would replace on a my99 car with an engine problem like what you have suffered.

the sensor is around £70 from your local dealer.

i would also look at replacing the fuel pump with a uprated walbro one just in case its a fueling issue as the pumps are also known to be a weak point.

also it would be a good idea to fit some instrimentation to keep an eye on the AFR (air fuel ratio) and a knocklink to warn you of engine distroying detination.