I have an '03 Evo 8 w/ rebuilt stock block, rebuild was about 25-30k miles ago. I'm getting oil in Cylinder 1 and it keeps fouling my spark plug in that cylinder causing lead idle (17+ AFR) w/ light misfire and super rich under boost (-10 AFR). Here's what I've checked

-Compression Test ~120psi across all cylinders
-Leakdown Test 3-4% on all cylinders
-Spark Plug Tunnel is dry, oil is NOT seeping from valve cover o-ring or valve cover gasket
-PCV valve
-Cleaned & swapped Injectors
-Swapped Coil Packs
-Changed Spark Plugs (spark plug again fouled out)

Recent Maintenance (after having this issue)
-Boost leak tested a million times, fixed all leaks
-Throttle Body rebuild (TB shaft seals, realigned throttle plate, Moly coat inside of TB, replaced TPS and re-calibrated, IACV clean/check)
-Replaced stock turbo, all new gaskets around turbo setup

Correct me if I'm wrong, but there's only 3 places oil can get into the cylinder
-Spark Plug Tunnel (completely dry)
-Valve Stem Seals (Leak down test was great, no smoke on startup)
-Piston rings (Compression test results were ok)

Everytime I pull the spark plug on that cylinder the top of the piston is obviously wet with oil (honestly not that much). There's no smoke at startup, which to me rules out Valve Stem Seals. I had someone tell me there was light puff of smoke in between shifts and I can faintly smell burning oil only under driving/load. That would point to rings, but my compression results seem fine. If anything there would have been a noticeable difference in compression on that cylinder if it were the rings and the fact that it was rebuilt about 30k miles ago. I emptied my catch can the other day, it was more than half full and I emptied it maybe 6 months prior meaning I have a lot of blow-by.. which also points to rings. So what gives? I've given this my best shot but I need advice at this point before I tear down the whole block.. Thoughts?

 

I don't think a leak down test captures valve stem seals. Being that the valves are closed and all. You can always pull the intake manifold and have a look.

 

Gotcha, thanks for clarifying that. I'm really hoping its the valve stem seals over the piston rings at this point. No smoke on startup really has me thinking its not the valve stem seals. Next chance I get I'll take a look but unless they are really bad how would I identify bad valve stem seals? Would pretty much have to pull, inspect and replace at that point right?

 

Sounds like rings to me.

 

Big bummer. Wouldn't I have a dip in compression on that cylinder though? Or is that not always the case?

 

When you pull the manifold you will probably see oil leaking down the valve stem or other pretty clear indicators. I expect if they are bad those valves will look a lot different than the others. When my exhaust valve seals went bad it was very obvious oil was leaking from the seals.

 

Same problem, oil in Cyl and sparkplug. I had perfect compression and leakdown and it still ended up being a ring. Was pulling my hair out trying to figure out what it was, including swapping to a new head with all new valvetrain, still same problem.

Swapped the rings and problem went away.

 

Thinking about the compression test, part of the factory procedure is to add oil into the cylinder and see if that raises compression. If it does then that means bad rings. Since you have extra oil in there already that might be screwing with the compression test. If the oil isn't obviously coming from the head then I agree with these guys that it's likely rings.

 

Damn.. yeah I have been chasing this for so long, I thought it was a boost leak for the longest time. I'll check valve stem seals first. I actually had my tuner do the compression & leakdown test. They didn't have time at the moment to dig any farther and I can do the rest myself anyways. Hoping it's just the seals or I'll be rebuilding this engine only 30k miles after a rebuild... thanks everyone!

 

Well, better than 4k in like mine.

 

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This^^

 

Pulled the intake manifold off tonight. Valves seemed clean, just as clean as the valves in other cylinders. It has to be the oil rings. Since I've never done bottom end work before, I'm wondering what the minimum parts are that I should order to rebuild this(stock rebuild). My thoughts are - piston rings, bearings, headgasket. Do you guys usually go OEM on this stuff? Will I have to pull the T case/trans? I just changed the fluids..