WiseMountainApe

I've got a 2004 Suburban 1500 5.3 Vortec V8 flex fuel. It started giving me a misfire code on #2 cylinder. I've replaced the spark plug, plug wire, ignition coil, and fuel injector, but still get a fouled plug with oil on it. I put a spark tester on it and could see a orange color spark so I see spark. I did a compression test and got 175 psi on #2, and 180 on #4 cylinder so that is encouraging. I am still getting that misfire with oil on the fouled plug. I've swapped ignition coils from #4 to #2 with no better effect. I"m not sure where to go from here.
Any help would be great.

hanky

It does sound like there may be a problem with a cracked oil control ring on that cyl piston.
How long does it run fine before the plug gets loaded with oil?

WiseMountainApe

The misfire comes back pretty much immediately. Would a leak down test help identify that condition even though I had solid compression in the cylinder?

tech2

do you get blue smoke out the tailpipe on start up or on hard acceleration?

WiseMountainApe

More of a faint white smoke. Oil on the dipstick is dark ( no milkshake). You rev the engine you get more smoke, but not alot really.

tech2

valve stem seals can leak and leave a build up of ash deposit on the center electrode of the spark plug. you will also get a puff of smoke on start up. Will not effect compression readings

post a pic of the plug

does it stop misfiring for a bit after plug replacement?

WiseMountainApe

Thanks for the reply. I did a leak down test on that cylinder and it seemed pretty solid. I cranked it up to about 100 psi and could hear air from the oil tube, but not the exhaust pipe, throttle body or radiator, so I guess you may be right about the oil ring. It seems strange that I have good compression, but oil is getting by the compression rings. Where am I wrong about that? Thanks!

tech2

what is the percentage of leakdown?has to be over a certain % to fail.

WiseMountainApe

Less than 10%. No noise from exhaust, throttle body, or bubbles in coolant. Only a faint hissing noise coming from the oil tube when I turned the psi to around 100.

WiseMountainApe

Thanks for you input. It turns out I had a broken rocker arm on that cylinder. Now that I have that fixed we'll see what other codes this truck has to throw me.