A tuning tale: BLMs say lean, plugs say rich

[XfireZ51]

Originally Posted by WARP TEN

This may be a little out of left field, but have you tried a slightly higher heat range of plugs? Maybe your plugs are running a little cool for your most typical driving and a change might show less discoloration. --Bob

Bob,

I had NGK 5 heat range in there. Not sure I would go any hotter. And the ground strap was indicative of the correct heat range for the motor. The plug coloration is inconsistent, w #2&4 showing brown to dark brown, nearly black. The other plugs on that bank were closer to “normal” w #8 being the leaner of them. The left bank was ok, maybe a bit lean, and all of that is indicated by the BLM split left and right. It averages out to 126-131 BLM, but that may be a 124 v 137 split as an example.
Frankly, the Autolites, which are a “projected nose” plug, puts the spark closer towards the center of the chamber volume. And the motor runs noticeably smoother w them. And it shows in the resulting MPG increase.
I’ll ohm the coils and plug wires next.
I’ll take it step by step and try documenting it here.

[XfireZ51]

Well plenum in process of being pulled. Clearly have intercyllinder activity going on. Specifically on right side. So if right side is coming in rich, then left side n eds to go lean in order to balance. But if the imbalance is due to uncontrolled air flow, then u end up tuning to compensate making the opposite side too lean.
Gasket on the right is the passenger side of motor which is running rich. Pucs are showing both top and bottom of gasket.

[mhobtr]

Are you going to check the injector housing gaskets also?

[XfireZ51]

Originally Posted by mhobtr

Are you going to check the injector housing gaskets also?

Yes. I’ll at least pull IH on right side. I’ll inspect from the top first to see if there’s a sign of oil seepage. By the looks of the plenum gaskets, I can see where at least part of the issue may have been originating.

[Ccmano]

Originally Posted by XfireZ51

Well plenum in process of being pulled. Clearly have intercyllinder activity going on. Specifically on right side. So if right side is coming in rich, then left side n eds to go lean in order to balance. But if the imbalance is due to uncontrolled air flow, then u end up tuning to compensate making the opposite side too lean.
Gasket on the right is the passenger side of motor which is running rich. Pucs are showing both top and bottom of gasket.

Dom, what is causing the discoloration of the plenum gaskets around each of the runner openings? Can’t tell from the photo. Is that oil or just sealer residue?
H

[XfireZ51]

Hans,

No sealer used on gaskets. I know Marc installs them dry. The wet spots are condensation. Its indicative of air leakage, and the worst of it is right around that #2 cylinder. Much less on left side of motor. I think the gaskets are FlatOut plenums. Frankly, I never liked their stuff. I just ordered a set from Jerry along w IH gaskets. The plenum bolts were properly torqued but pretty clear that plenum was not sealing against gasket. Interestingly, motor idled well and ran pretty well. Without a datalog and looking at the plugs, someone would have left it alone.

[Ccmano]

Originally Posted by XfireZ51

Hans,

No sealer used on gaskets. I know Marc installs them dry. The wet spots are condensation. Its indicative of air leakage, and the worst of it is right around that #2 cylinder. Much less on left side of motor. I think the gaskets are FlatOut plenums. Frankly, I never liked their stuff. I just ordered a set from Jerry along w IH gaskets.

If that’s the case you have quite a lot of air leakage. It will be interesting to see the IH housing gasket. I’m running the thicker gaskets Jerry offers, although I have found they require a retorque after a few days of running.
H

[XfireZ51]

Hans,

I think you will see this type film on most. What’s important is to see if the plenum is sealed at the perimeter from the outside and between cylinders. The film u see on the gasket is oily, likely from the presence of oil vapor from PCV. In particular here is that the #2&4 cylinders appear to be “sharing” the airflow which would explain the color of those two plugs specifically. The other cylinders have same film but to a much diminished extent and not the cross travel u see between these 2 cylinders. First pic is #2, second shows trace of flow between 2&4 similar to what we saw on gasket. In the other set of pics u can see the flow of the oil film down the runner from top of IH. So the question now is, do I stop there or go on to removal of IH’s as well?

[A26B]

Just for peace of mind, you might try screwing your plenum bolts into the injector housing, to just hand tight. Check to be sure the gap under the bolt head to the top of the injector housings is at least 1/16" less than the thickness of the plenum at each bolt hole location.

With blind tapped holes, it can be difficult to tell when the bolt is fully clamped or out of threads.

Also, about the allen drive pipe plug in the injector housing coolant port; What if it's seeping coolant into the adjacent intake runners? How would you tell unless it was significant? There is so little "meat" there to tap for that plug. I have always been concerned about it sealing properly with probably less than 2 threads engaged.

[XfireZ51]

Originally Posted by A26B

Just for peace of mind, you might try screwing your plenum bolts into the injector housing, to just hand tight. Check to be sure the gap under the bolt head to the top of the injector housings is at least 1/16" less than the thickness of the plenum at each bolt hole location.

With blind tapped holes, it can be difficult to tell when the bolt is fully clamped or out of threads.

Also, about the allen drive pipe plug in the injector housing coolant port; What if it's seeping coolant into the adjacent intake runners? How would you tell unless it was significant? There is so little "meat" there to tap for that plug. I have always been concerned about it sealing properly with probably less than 2 threads engaged.

Jerry,

Thanks for the tips on checking bolt clamping. The allen plug has been there now for probably 7 years. No indication of coolant loss so far. The dampness u see on the gaskets is of an oily nature