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.

 

as my FPR hose slipped off under full boost.

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

 

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.

 

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?

 

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?

 

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.

 

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?

 

easy test...take off ur oil filer cap and if smoke comes out guaranteed cracked ringland
...thats wuts mine was, oh and i had oil pouring out my cai, but no cel