| Can anyone help with this issue? About 10 years ago I did a major engine overhaul and rebuilt/cleaned everything. All the plenum water lines, EGR, PCV lines and all the head cover-back-to-intake hoses were removed/eliminated (even the 2 with the restrictors and flame arresters). At the time there was a lot of thick oil sludge and oil in all the high pressure side black intake pipes coming from the turbo compressors, which made sense since a lot of the oil vapor would be recirculated back into the plenum and the low pressure suction side of the intake. There was also a lot of soot in the intake, I'm guessing from the EGR. All the oil vapor lines going to the intake were disconnected, and little breathers/filters were instead added to the head cover oil return hoses, to allow relief of crank case pressure in case of pressure build-up. The EGR was also removed and disconnected from the exhaus, and both sides EGR-to-intake pipes were blocked off. This should have kept the plenum and the intake pretty clean, kinda like older cars, right? Well, I just removed the plenum tonight to try to upgrade to larger injectors, and I was very surprised to see there's lots of oily residue in the intake (not as much tar or sludge this time, but more like dirty carburetor cleaner mixed with a little bit of burnt oil). The inside of the plenum was dark with that coated oil vapor color, it was probably that way last time too, I just don't remember too well, but this time there was also a lot of debris similar to sand and fine aluminum dust in the back corners of the plenum on the walls behind/below the balance tube openings, in the stagnation area in the back of the plenum where no. 5 and no. 6 ducts meet the throttle ducts. Where is this crap coming from? Upon inspection, the black intake pipes and the throttle bodies are completely clean. I have taken one turbo off (driver's side), and the compressor wheel seems completely fine. The other turbo also seems fine judging from its turbine wheel spinning easily, although I haven't seen the compressor side yet. Judging from how clean everything looks in the intake up to where the throttle valves are, none of the debris is coming from the air intake. That only leaves one possibility: Could all this oil and debris be coming from the cylinders or the valves? Can the air flow backward through the plenum, as in some exhaust forcing sir back into the plenum? The intake valves look pretty clean, although the valve stems and valve tops look very dark, almost black. One thing worth mentioning is that my turbos have been leaking oil for a while now, both dripping down and out into the exhaust, probably the last 7 or 8 years. There was a lot of oil smoke in my exhaust during acceleration. I'm planning to change turbos this time while I'm doing all this work. Could my leaking turbo seals somehow have contributed to the burnt-like oil in the plenum? As in oily exhaust back-flow when the exhaust and intake valves are both open? The driver's side exhaust manifold that i can see (turbo removed) is completely dry and clean tho. Luckily it looks like none of the sand-like debris made it through the plenum and to the cylinders, because the curved upper plenum ducts and the lower intake/plenum are completely clear of any of this debris. It seems that all the solids in the flow dropped out and were deposited at the back edge of the plenum, as described earlier, where flow stagnates and the velocity is low, kinda like river sedimentation/erosion. I'm at a loss here, as far as both where the oil and the solid debris come from. Does anyone have any idea? Has this ever happened to anyone else? I'd like to avoid this in the future. This should not be happening. The intake should be clean, since no oil vapor is going into it like before, and the debris can absolutely not continue to get into the intake somehow. I'm going to search further to try to find the source of the debris. This cannot happen again in the future. I'm also going to do a compression test to make sure the engine is ok. Is there an easy way to test the intake and exhaust valve seals for oil leaks? What are the symptoms of leaky valve seals? Is there any way to test the valve seals? Just want to figure out why I found oil residue in the plenum, but not upstream of the throttle valves. Also, the idle air bypass in the balance tube is completely clean, no oil residue there. Anyway, open to suggestions / opinions / other people's similar experiences.
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