Sooty #7

[Paul Workman]

Is it oil, or is it fuel...is the question.

What we have observed/know:

-compression, bank-to-bank is clearly a little higher on average on the right bank than the left, and #7 is second to highest on the left (lowest average) bank
-Loop resistance thru the coils comparable with non-affected cylinders
-gray/black noticed at exhausts
-all HOT(?) injectors resistance within tolerance
-plug porcelain has a black soot layer and inside steel surfaces have crusty material evident and unique to that one cylinder
-motor (you say) seems to run strong - no issues noted
-headers with SW "X" pipe, Dynamax 17288 twin outlet mufflers w/ an NPP on each of the two mufflers

Black sooty plug and some crusty deposits as well, and observed black/gray exhaust emissions at WOT - points to OIL (most(?) likley) or excessive fuel

Supposing, for the moment, it is oil affecting ONE cylinder. Where can it come from?

A broken ring? Compression test = inconclusive. What would a leak-down test reveal?

Bad or missing valve guide seal? Possibly. If so, one valve in the lot of them showing signs of coking wouldn't be a surprise, considering the soot issue. (Now if we had a coolant leak in the IH, the valve(s) would be cleaner than all the rest (ask me how I know...) But, if it IS a guide seal, nothing short of pulling the cams is required, and that usually means pulling the motor to facilitate re-phasing the cams. Then the question is whether it is worth it? But, of course if you did pull the cams to install new guide seals, when the cams are reinstalled their phasing can be checked and/or matched with those of the other side at that time as well...

Your motor is ported. Could there be oil seeping through one of the runners? This has happened to more than one ported head! Any black streaks initiating from a spot of the sides of runner walls closest to the valve springs? (Yours wouldn't be the first, I can tell you! You might need a probe to look down there, unless you remove the IH too.)

Assuming it is a fuel issue:

Injector leaking fuel? A fuel pressure leak-down test would indicate leakage, but just where isn't so easy to say. However, if the plenum is off that would be a good time to do a double-elimination and swap injectors from a good cylinder to #7, but then too install different injectors to take the place in the donor cylinder. (Or, you could just swap between two cylinders, but then you'd have to pull the plenum again should what was originally #7's injector(s) prove bad.)

Hmmm.... That's all of the testing I can think of that you may not have done. But, often a test results in new evidence that can lead in an unexpected direction. Would be interested in what you find.