I've had two different mechanics look at my V7 JDM STI and they both suspect different faults. One thinks I've fried a piston and the other thinks it's probably only a head gasket.

The fault occured whilst driving hard in 6th gear. For some reason I lost Power and when I pulled over it was only running on what sounded like three cyliners. It didn't cut out at all or make any loud engine type noises and still managed too get me 2 miles home(slowly). It still starts and idles (on three cylinders) and hasn't lost any water or oil to speak of. The only patch of oil I can see is by the turbo.

If anyone could shed any light or input any opinions as to what might be or is most probable to be wrong, I'd really appreciate it.

Thanks for any replies.

 

Compression Test and a Cylinder Leak Down Test will pin point the exact
problem if it is an Internal fault with the engine.
Any fault codes stored in the ECU ??

Mick

 

It has lost compression on cylinder 4 and a bit on 3 I've been told.

But would it run at all if the piston has gone? Or should I have clouds of smoke coming out the exhaust?

 

quite likely the piston has melted but still retains enough of the oil control ring to limit smoke.............

alyn

 

I'm doubtfull the piston will have fried, the STi7 has forged pistons as standard, unless your runnig silly boost without mapping, pistons should be fine. Number three normally goes on other engines.

I'd say head gasket, when you say you've lost no water or oil, have you actually checked the water & oil levels? It normally goes between water way/oil way/bore & bore, not normally visable externally unless the car has been hydraulic'd.

Pressurise the coolant system, if it looses pressure, that would confirm my thoughts.

STi7's dont fry pistons

 

Forged pistons are not indestructable. They melt almost as easily as cast ones. Any piston can melt....just because one cylinder may be more common that others, doesnt mean it doesnt happen to others.

Either way, its engine out time for a proper inspection, rather than speculation.

 

I hope you're right! Thanks for the input. I'll have some one check what you've just said.

I'm holding on to that glimmer of hope that my £1k budget can save the scoob!

 

If its the piston, the coolant wont loose pressure, thats a good starting point, takes 10 minutes to do and will give a good indication as to what the problem is.

Forged pistons do melt but not a readily as normal cast piston otherwise you would fit forged pistons when building a bullet proof engine, you'd just stick standard pot cast jobbies in.

Diagnostics of the engine will decide whether he will sell, or repair. I'm only trying to help, cheap first is the obvious thing to start with imo, not, "ah just pull the engine and wrip it apart, thats the only way to see what wrong with it"

 

that'll be why there are quite a few "warranty" blocks doing the rounds with piston/bore damage??

we see quite a few failures of the STi hyperpeutic (spelling??) pistons - n0.3 not generally being the most common

best advice is as above and get it checked correctly before starting to pull it to bits

alyn

 

The EJ207 had forged pistons up through v7. Since that time Subaru switched over to hypereutectic, version 8 onwards meaning version 7 had proper forged piston fitted from what I know.

 

there is another thread discussing this and Zen confirmed that the STi8 uk has forged pistons.

 

What other things could cause a car to loose pressure on one cylinder? Are there many possibilties?

 

Head gasket, Piston damage, or valve/seat damage.

Any mechanic with half a wit, should be able to make a proper diagnosis fairly quickly after hearing it running ( or cranking over if it wont start ), and doing a compression/leakdown test, as well as a quick look at the plugs.

If they cant, take it elsewhere.

 

The last car we did that displayed your symptoms had burned out an exhaust valve.

As has been said, carry out a cylinder leak test, as this will tell you exactly where the problem is before you decide wot to do next.

Phil

 

I've got to say I'm glad I posted this. I thought the scoob was doomed and you've all given me plenty to get checked out. Any more suggestions are welcomed. Thanks all.

 

m8 i have a version 3 sti which runs very lumpy on idel ( you would think there was a piston gone ) but the car has been runing like this for about 6mths . Got all the usual checks done and every think came back ok !!! so i had a simtek ecu fitted a few weeks back as i was told to get the fault tuned out of the car , but when the mapper was tune,in it he said there was a leak between cyclinder 1 & 2 so he has now to split the engine to find out whats causing this he thinks it maybe a cracked head gasket so do,nt worry to much m8 incase its something as minor as that
P.S my car was not using oil or water and comprision tesk 100% ok

 

Thanks m8. There might be some hope left then. However, mine idles but won't rev past 3.5k really. I gotta grand in reserve to sort it. If that doesn't just about cover the problem then it's gonna have to go. I hope mine is a head gasket!

 

Take a search for JamesVTS and his tale of misery...

WRX in this case, but it's eaten a piston.

Sorry doesn't look good.

DunxC

 

Forgot to add that it has been said that some/all STi8 "Type UK" have forged piston fitted, cheers mate.

 

regardless of factroy "forged" or later hyperpeutic pistons they fail just the same (albeit maybe slightly higher) as std ones, we re-build quite a few of these

alyn

 

https://www.scoobynet.com/general-te...lp-my-wrx.html

take a look at that, tried many things, sounds like same issues youre having, sorry mate

I got a new engine in the post

 

Except listening to sense, and removing the pistons to inspect them when you had it apart.