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[pisymbol]

How do you tell? Should there be smoke? People talk about a rough idle, is that all the time or can the car still idle properly in some instances. Any CEL's thrown?

[roninsoldier83]

On my former WRX, cracked my #4 ringland. For reference, it was a fairly minor crack, so car still had pretty good idle, was a little low on power, but actually even that wasn't too noticeable. No noticeable white smoke either. Compression test revealed #4 about 50psi low.

Anyway, I received a flashing CEL, with cylinder #4 misfire code. Although I pretty much knew something was likely damaged after I heard audible detonation under 20psi of boost, as my FPR hose slipped off under full boost. Shortly after I started receiving the flashing CEL letting me know there was a misfire on #4.

[Digitalfiend]

Originally Posted by roninsoldier83

as my FPR hose slipped off under full boost.

Damn, how does that happen (assume FPR is fuel pressure regulator)?

[santacruz02]

On my last motor I cracked 3 of 4 ring landings. Rough idle, smoke on start up and smoke while under mid to high acceleration. Check your oil level. Mine was only found by a leak down test, as it was not the compression side but it affected the oil ring. Hope this helps.

[pisymbol]

Can you guys define rough idle? Was that all the time or only during a cold start? Did the idle move up and down constantly or just sit at the wrong RPM range?

Finally, how drivable was the car with a cracked ring?

[combatp21]

Originally Posted by santacruz02

On my last motor I cracked 3 of 4 ring landings. Rough idle, smoke on start up and smoke while under mid to high acceleration. Check your oil level. Mine was only found by a leak down test, as it was not the compression side but it affected the oil ring. Hope this helps.

What does a leak down test involve?

[santacruz02]

Originally Posted by combatp21

What does a leak down test involve?

I did not perform the test, my local subaru dealer did. Corret me if i am wrong but I thought it was similar to a compression test but there is another needle that moves back down to 0 as compression is lost.
So the car is turned over then I assume he watched the gauge.

as far as rough idle, my car was shaking could have been a little low on the rpms but I don't recall. and yes it smoked everytime.
I don't know your setup, but at stage 2 there is alot of blow by causing oil to get into the intake plumbing and intercooler, this too can cause a smokey start up I think.
idk if bent valves can cause that but im sure thats something else you wnana check into. either way, do one of the two tests. should reveal some info for ya.

[leeroix]

LEAKDOWN TEST= Differential cyllinder pressure test. with pistons at top dead center, compressed air is pumped into the combustion chamber via the spark plug hole. a guage on the regulator lets you know how much air is being lost to ring blow by, or burnt or other valve damage, (intake or exhaust) usually this test goes hand in hand with a compression test and lets you pinpoint any internal damage.

[jasv11]

I cracked the ringland between the top 2 rings of piston #2. No smoke No burnt oil,no noises, I just lost power,went from running 114 mph at the strip to running 108mph and did a compresssion test and was down to 70lbs in # 2

[pisymbol]

Originally Posted by jasv11

I cracked the ringland between the top 2 rings of piston #2. No smoke No burnt oil,no noises, I just lost power,went from running 114 mph at the strip to running 108mph and did a compresssion test and was down to 70lbs in # 2

Wow that sucks. Did you have even a "rough" idle?

The other question I have is can a cracked ring cause the engine to just shut off during driving?