Black oil, loss of power. 91

[docdread]

91 with 165k miles. Running strong till about a month ago, sudden rough idle, loss of power across all gears..very slow acceleration. Changed plugs, rotor, cap, wires, fuel and air filters with only a slight improvement. Not burning coolant (atleast I don't think so) no moisture in exhaust except on cold start, but even then no white smoke. Oil is jet black 50 miles after oil change, happened twice. All cylinders firing except 6 (furthest from radiator) Plug no 6 has serious carbon build up, replaced again and carbon builds up almost immediately. Replaced O2 sensor when I smelt fuel in the exhaust, good results but a lot of carbon lines the exhaust. Used seaform in fuel and into vac lines, not much help. Thought the cat convertor was clogged, replaced it and not help. Timing belt was replaced about 20k miles ago.

Biggest symptom is black oil, no power, no 6 cylinder carbon and apparently little/no ignition in it (6) Talked to a mechanic over the phone and he says 90% chance no 6 compresion ring snaped or something and its dumping fuel into oil. Whats you take, I will do anything to save my Cress.

[kamesama980]

to share my tc.net answer here:
to fix it you really need to get your hands dirty or start emptying your wallet. compression check and leakdown test #6 and probably the other 5 cyls too. if compressions low, do a leakdown test (quick and dirty, regulate compressed are down to 5 or 10 psi and listen at the dipsick, tailpipe, and throttle (and radiator cap for a 7m). if compressions not low, you need to figure out what IS missing (fuel or fire).

though really it's time to start engine shopping.

[docdread]

Thanks Kamesama
Progress report: All evidence pointed to a busted ring, but then I said what the heck let me get dirty. Removed throttle body then upper intake manifold. Low and behold, it looked like the inside of a truck exhaust. 3 to 6mm thick black semi oily stuff lined the inside of the throttle plate and the entire intake manifold. In all the stuff could almost fill a small cup. Storm came and I couldnt reassemble today unfortunately. By the way, that old catalytic converter was restricting air. I realised this because previously at speeds above 60mph if I let go of the gas there would be a grunting sound which would disappear as soon as I hit the gas again or if the speed fell to about 50mph. This stopped with the new converter.
Anyway, when I cleaned the throttle body about 6 months ago it wasnt so bad... I remember peeking inside the intake manifold and thinking eventually I would have to remove and clean it as well.. however it wasnt anything like what I saw today. The oily carbon was mostly severe in cylinder 1 intake, and less so in 2, slightly less in 3 and so on. 6 still had a lot, but maybe half of what 1 had.
By the way, exhaust fumes has unburnt gas in it, engine oil gets thinner and blacker by the mile with fuel. I am hoping the engine was simply starved of oxygen, will let you know when I reassemble.

[stepho]

Worn or broken rings cause caused blow-by, letting hot gases enter the crankcase which pushes oil vapours out through the breather hose into the inlet.
Which would explain the gunk on the throttle body.

- Stepho