Sparkies No Beno

I bought this Yukon 2 mths ago and don't know its mx history.

Pulled the spark plugs today so as to soak my combustion chambers with solvent as part of TSB 10-06-01-008M(see this link)
https://f01.justanswer.com/ebrock63...il+Consumption,+MIL+ON,+Engine+Runs+Rough.pdf

My 6.2 L92 has 132k miles. How old to you think these these plugs are? It was purring like a kitten, never missed a lick, wasn't throwing any codes.

I got new ones coming, wires too, but I cleaned them up and plan to use them again someday.
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What's their gap? They may not be so old, but if I was gonna guess, I'd say they were original. Usually, those types of deposits are from running fuel with lots of additives. How'd you clean 'em so well?!

Chris, the gaps were .040" to .043". .040 is what they're suppose to be gapped at I think, so they weren't bad in that respect. I think all the grud came from all the oil its been burning because of the wrong valve cover and lack of an AFM oil deflector. At least that's what I'm hoping the problem has been since I'm doing all this work.

I cleaned them up in my HF media blast cabinet, aluminum oxide and a wire wheel bench grinder.

These plugs are Iridium GM# 12571164 - ACDelco 41-985, which have now been superceded by 12621258 or 41-110.

so if the plugs have that amount of combustion sediment how will you effectively remove the dissolved "solids" from the cylinders after the solvent turns them into a corrosive slurry? imo id rig up some kind of a shopvac and small tube to suction the majority of it out as opposed to simply cranking it out of the open plug holes. do you have a boroscope? how much is on the piston top's? i just dont like solvents in close tolerance friction areas. the blowby is solved, plugs cleaned/replaced maybe consider just leaving the crowns as they are and time will sluff the deposits off and out the exhaust? i have way to many opinions! your work/effort is professional and experienced but dont fix it til breaks? also since the exhaust is disconnected from the manifolds run the scope down there and check the cats for signs of clogging/deposits?

thompsoj22 said:

do you have a boroscope

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John, Yes I have a scope, but I'm not worried about it. I think whatever's in there will come out the exhaust sooner or later.

thompsoj22 said:

dont fix it til breaks

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IMO it was broke. I was collecting 1 oz of oil for every 100 miles in the catch can I had installed not long ago. Maybe what I'm doing will help?

thompsoj22 said:

run the scope down there and check the cats for signs of clogging/deposits

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There are fine screens upstream of the cats, they're probably a mess. I'd think to use a crow bar and turn them into HI FLOW cats, but I don't know how the ecm would like that? Where I live they don't do the sniffer thing for our annual inspections.
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That's not a fine screen, that's the catalyst. OEM cats ARE "high-flow". Every tiny "hole" that you're looking at in those pics is the end of a "tube" of catalyst through which the exhaust flows. If you look at them head-on, it looks like a screen. Viewed from a slight angle, you can tell they're tubes. The PCM would throw catalyst inefficiency codes if you punched 'em out. It wouldn't affect fueling or anything, but you'd have an SES light on at all times.

donjetman said:

Chris, the gaps were .040" to .043". .040 is what they're suppose to be gapped at I think, so they weren't bad in that respect. I think all the grud came from all the oil its been burning because of the wrong valve cover and lack of an AFM oil deflector. At least that's what I'm hoping the problem has been since I'm doing all this work.

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I would expect burned oil to be black instead of ashy deposits. But, maybe synthetic oil burns like that. You use synthetic?

Never in my life have I seen spark plugs like that. Never ever never. Don't know what to make of those.

The cats are taking a beating. You can hollow them out but will need to turn off the lower O2 sensors with a tune or do or buy those things that trick them into thinking the cats are still functional.

I'm running 41-985s in mine and the original set came out looking about like your last photo.

People pay good money for used OEM cats. If you don't have visual inspections and want them gone, either get headers or have both entire cats cut out and replaced with pipe.