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Old 11-03-2019, 10:14 PM   #1
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Location: Hudson, Colorado
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98 lumina LTZ 3.8 smoke out the exhaust

175,000 miles and it smokes in stop and go traffic and after it idles a while,
Hard to tell if it's white or blue smoke.
Pulled the plenum and LIM, Found out the LIM gasket's had previously been replaced because the fel-pro part number's i took off are the same as i put on.
Plenum was also new and had the updated egr tube in it already, But i replaced the plenum anyway.
Inside the plenum and on top of the LIM was wet with oil and the area with the hidden bolt's for the LIM were full of oil.
When i installed the LIM gasket's i put sealer on all the LIM bolt's. Torqued all the bolt's and torque turned as instructed.
The o-ring under the pcv valve was missing, but when i replaced the plenum the new pcv valve had a o-ring on it.
While the LIM was off i looked at the intake valve stem's and they showed no sign's of oil leaking past the valve guide seal's or any deposit's.
One note, This all seamed to start after i changed oil to a napa brand full synthetic 5W-30 oil.
The engine still smoke's after doing all of this work and now it appear's to be blue smoke.

I ran a compression test with my 40 year old Matco compression gauge and all pressure's are between 125 and 130, Picked up a Harbor freight compression gauge and they all read between 105 and 115.

I ran a cylinder leak down test with my 40 year old Mac tester and there all at 3 to 7% at 90 psi. I picked up a Harbor Freight leak down tester and they all measure between 8 and 15%.

All the spark plug's showed no sign's of burning oil or oily.

I'm thinking the pcv system is sucking too much oil into the intake, But i took a old pcv valve and filled it with silicone and let it harden to block off the pcv and it still smokes and there is no blow-by in the motor when doing this.

I want to drain the coolant and pull the throttle body and see if i can use a bore scope to see inside the plenum. Look at the 2 hidden bolt areas and see if they have pool's of oil in them.

If there is no oil in the plenum or on top of the LIM, then the only thing i can come up with are the valve stem seal's. There is a bulletin from GM on the exhaust valve seal's going bad and causing oil burning and blue smoke.

Any other thought's anyone?
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