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.

[Ccmano]

Dom,

Didn't you have an issue when the porting was done with a pinhole leak in the injector housing? I wonder if this might be the same issue.
H

[ssrszz4]

I know that '90's didn't have exhaust valve seals and was designed that way on purpose.



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[XfireZ51]

Originally Posted by Ccmano

Dom,

Didn't you have an issue when the porting was done with a pinhole leak in the injector housing? I wonder if this might be the same issue.
H

When I first ported the injector housing, I went thru the bolt boss at the very front of the IH. Vacuum leak into #2 primary runner. Welded that.
There have been other cases of oil seepage through a very porous casting of the cylinder head runner.
#7 is close to the PCV. Wonder if its related to crankcase venting and possible lack of restriction between IH and cylinder head.
Question for Mr. Haibeck.

[XfireZ51]

Interesting post I ran across while doing research on another topic. This appears to describe what I observed after doing the compression check.Same bank as well.

http://www.zr1.net/forum/showpost.ph...53&postcount=1

[jss06c6]

Dominic,

Any updates?? Very interested to learn what is causing the fouling of #7 plug.. sure hope it's something "reasonably" easy to fix..

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[XfireZ51]

Originally Posted by jss06c6

Dominic,

Any updates?? Very interested to learn what is causing the fouling of #7 plug.. sure hope it's something "reasonably" easy to fix..

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Right now there isn't a further update. At this point, we'll begin looking at it after the 4th holiday or sometime after that. Given the results of the compression test and checking of injector and plug wire resistance, there's nothing obvious. It could easily be a leaky injector. But right now that's speculation. It could be something more involved. I'll have Dr. Polatsidistein have a look and I will update.

[jss06c6]

Thanks. Watching with interest..

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[Paul Workman]

A fuel injector leaking would show up if you pressurized the fuel rail and observed the time it takes to bleed off pressure.

As I recall, it took over 15 minutes to bleed off the first pound of pressure when I did mine the last time, once I found the leak (a bad check-valve in a fuel pump).

One other thought: isn't the vacuum line for the pressure regulator just about directly over the #7 plenum runner? You know where I'm going...!

Just some things to ponder before pulling the motor...

[XfireZ51]

Originally Posted by Paul Workman

A fuel injector leaking would show up if you pressurized the fuel rail and observed the time it takes to bleed off pressure.

As I recall, it took over 15 minutes to bleed off the first pound of pressure when I did mine the last time, once I found the leak (a bad check-valve in a fuel pump).

One other thought: isn't the vacuum line for the pressure regulator just about directly over the #7 plenum runner? You know where I'm going...!

Just some things to ponder before pulling the motor...

Well yes the PR vacuum line is by #7 but plenum volume is supplying vacuum so its hard for me to gather how it discriminates on #7.