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I would think no,because if its leaking,in higher boost levels,the fuel would increase to the air,so it goes more rich,and i never seen a melted piston in a engine running rich,only lean causes melted pistons. maybe a fuelingproblem,injectors bad?? Any pics??

Ps: i mean leaking,not permanently open.
 

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would a permanently leaking dump valve cause a melted piston??
cheers
liam.
Unlikely, but not impossible. Depends if the car is MAF or MAP based, and if it is MAP based, where the pickup for the MAP pipe is.

More likely... bad tuning, too much boost, not enough fuel, wrong spark plugs or a knackered crank angle sensor or other component failure like a fuel pump perhaps.
 

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Discussion Starter #5
the car was set at 10 psi, just had new headgasket and slightly bigger turbo....btw it was on a ca18det if that makes any difference.
The dump valve just let air pass thru...as in might as well not have been there, just a hole if you get my drift.
cheers
liam
 

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Of course it would, you have a hole between the maf and the piston so it runs very lean, the result is melted pistons and another blown CA18DET
Actually its not "Of course" at all. Generally on the dyno with a car that has a hole between the MAF and the inlet manifold side (IE. Dump Valve) most of the air is wasted out of that hole, so the airflow meter is sucking ten tonnes of air it doesnt need for combustion and the mixture goes excessively rich.

The hard and fast of it is that with a jammed open dump valve the car will be lean on cruise (ie. Its drawing in unmetered air as the pipework is in vacuum condition) and rich on boost as its blowing air out that has been metered in, thusly the mixture to the engine has a greater fuel quantity than it needs.
 

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I know it would run rich on boost, but the melted piston would have been caused by the off bosst lean mixture. That was my point.

Anyway the answer to the original question is yes.

:)
 

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...but the melted piston would have been caused by the off bosst lean mixture. That was my point.
I disagree. Sorry and all. Cruise on a standard car is about 15/15.5 AFR, much leaner and it wont even pull along, say the 16/17 mark, so I find it highly unlikely that its run lean enough, for long enough at cruise to do any damage - lest we forget how little load there is at cruise. Far more likely to have the wrong plugs, dicky injector, fuel pump etc.

Lean cruise may be a factor, but to proclaim straight away that its definately the problem is rather rushed, when its far more likely that piston damage has occured on full load. Could be timing or any number of issues.
 

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Agree with dan0h on this one - a lean mix at cruise is under much less cylinder pressure anyway, and on boost / wot where cyl pressures are highest it would run dog rich.

The car will also be in closed loop at cruise so to a certain extent it would richen the mixture back up to the proper value.

Is the car on std ecu or re-mapped? Everyone jumps on lean fuelling for problems with turbo cars and whilst it's definitely a killer timing which is too advanced by 2-3 degrees at WOT will cause problems pretty quickly.
 

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As i said,it can´t be only the leaking dumbvalve,if so all cylinders would have been damaged,but you are saying one piston,so it must be something else(Mapping,Plug´s or whatever ) ;)
 
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