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loss of power between 5-5.5k revs HELP!!!


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hey guys,

i am currently having issues with my Impreza hatchback sti (ej257). 

as you're on throttle it builds up and as soon as you hit higher Rpm it struggles to maintain the power and it begins to lag and sounds like a rattle coming. I've not long taken the intake pipe off the turbo to check for play and there wasn't any as far as I could tell. has anyone had any similar situations that could shed some light? there is no tell tale sighs of the notorious head gasket failure but I'm losing coolant and oil but no external leaks either which make me conclude back to the turbo

My car has limited modifications as it only has a hks catback system, a GFB hybrid bov and nothing other than that so I am pretty clue less on what is going on. please help.

thank you. Sam

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If it's a electrical or fuelling missfire,  you'd normally get a eml light or code stored . So maybe get the ECU codes checked before chucking parts at it .

But unfortunately it does sound like early symptoms of headgasket and the 2.5 ltr block is the most common to fail .

Subaru's hardly ever mix oil and water , like most inline or "V" engines.  They tend to start to push combustion gasses into the coolant on boost at first   then start to burn coolant as the gasket wrap gets worse .

Best way to check if you're getting the beginning of h.g failure symptoms,  is to get a hydrocarbon coolant sniff test done (as suggested above ) 

Best of luck and hopefully its something less expensive, like a cracked rad or failing coolant pipe .

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Using some oil isnt umcommon, although depends on amount. Loosing water is a bigger concern. Add the two together and as said above doesnt sound good.


Best bet get a specialist to check it out including the above mentioned sniff test.

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