GMC Repair: Oil consumption, valve stem seals, brown ash

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I have a 1998 GMC Z-71, I have a couple problems that I can't figure out. 1) I have 170,000 Highway miles have always used mobil 1 10/30. It uses a quart every 1000 miles, doesn't leak, i have only seen it smoke once. while I had gotten on it getting out into traffic. Wheres the oil going? 2) Cruising at a decent speed 45-50) I feel like a shimmy and it sounds like the driveshaft is rubbing something, could it be Trans or transfer case?
Answer -
Your oil is most likely gettin past the VALVE STEM SEALS or you could have worn oil rings on the engine pistons. Probably a combination of BOTH.

As to your shimmy there are numerous possibilities.

When you are at a stop sign and you shove the accelerator rapidly to the floor as if drag racing, Is there a shimmy or shuddering effect ?.

No, There isn't a shimmy or shudder. It's like something is trying to engage or the transmission doen't want to downshift from overdrive. I have been told they've had a problems with both trans. & Transfer cases.
As far as the oil, the sparkplugs only on the passenger side are corroded with reddish brown ash.


autohelp
Answer -
You stated: "the sparkplugs only on the passenger side are
         corroded with reddish brown ash.

Question: What about the drivers side ?.


If you did the test as I ASKED you to do, What was the outcome ?.

Without actually driving the vehicle, this vibration could be anything.


autohelp


Yes just the passenger side plugs were fouled, the drivers side looked fine.
As far as shoving the accelerator to the floor it will bog down then spin the wheels, no shimmy or shuddering. The noise usually happens under 2000 rpms, Like I had stated it feels like something is dragging the driveshaft all of a sudden. It doesn't do this all of the time but I would like to get it fixed before I'm 1500 milesfrom home.

Answer
To determine IF the piston oil rings are at fault, You will need to have a DRY and WET compression test performed on each cylinder of the engine. This will tell you the condition of each engine cylinder.


As to the noise it could be:

axle cv joints.
transfer case problems.
drive shaft(s( problem(s).
transmission problem(s).
axle bearing(s) problem(s).

Without actaully driving the vehicle and EXACT diagnosis is impossible.



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