Basicaly my mates car a y reg classic uk turbo (prodrive car) number 2 piston melted a year and half ago i stripped it down then and then he sent it to a very well known engine builder i dont want to name them yet as i am not pointing fingers i have just stripped it again today after 13k miles and now piston 4 has melted! my mate had a full rebuild crank bearings pistons etc new maf then and another 12 months later as he was told this was the cause first time around, i was not convinced then but i was not to clued up then on impreza's, i am a mechanic, bentley trained and work on all types of cars and have built many engines and the 1st thing i always do is find the cause but he sent the car away but this time i get the build but i have only one idea at the moment that the injector for no4 cyl is not supplying enough fuel as its the first to get it on the rails any ideas are welcome here are some pics


he does not drive this car to hard he loves it to much and it only has a de-cat down pipe green panel filter and prodrive ecu but i cant see this causing the damage as it has not had a boost increase its running 1.1bar which it did before de-cat and it doesnt spike either as you may guess he aint happy as he did spend a few grand on this rebuild. I have no problems with the builder as i do talk to him when i need help and advise (through work) but i have found a few things i didnt like when stripping it but thats not in any way the cause any one had no4 melt before on here?

 

anyone?

 

has the car been altered at all ie more boost bigger turbo ect with incorrect fueling if not and standard the 99-00 cars tent to over fuel on high load but your pic's look like the car has suffered heavy det (cooked the piston ) as not being the first time if standard car and not messed with it would have to be incorrect maf voltages making car run lean (99-00 cars have weak maf's often difficult to diag) could be one of the unlucky ones

 

Yup all those little indents are signs of massive det going on.

You always remap with any new engine regardless hence why it's gone bang.

Not running it on normal ul by any chance?

 

yes i would be checking what map the car is running along with boost and type of fuel.
i dont think 1.1 bar is standard fora uk prodrive car.

 

cheers for input guys the car is only run on shell v-power and never any other fuel the det that has killed the piston is only on number 4 cyl the other 3 are perfect i will post some pics of them soon, the maf i know they are sh1te on this age car but it is replaced without fail every 12months since built, the engine builder is one of the most respected on here and on the invoice it the car has been checked and all ecu perameters were correct which is either true or not? but that amount of det on only 1 cyl can only be pinned on fueling to that number 4 cyl its the only thing i keep coming up with no signs of high oil temps either
But would a maf problem cause that amount of det on only number 4cyl?
also the boost hits 1.1bar and tails back to 1bar as revs rise and the turbo is a td04 with standard 2 port boost solenoid all rubber pipes standard and clean dont make any sense does it

 

Does sound like insufficient fuelling to cyl.4. I'd be inclined to remove the injectors one by one and labelling them with the their cyl. number using a marker. Then have their flow-rates physically checked. I fully expect # 4 to be significantly down compared to the other three.

Just my 2'penn'eth.