2004 Tahoe engine issues

[Heldju]

Hi
I have a 2004 Tahoe with approx 130000mils on it. During the last half year it has started to use oil. It uses the same amount of oil between oil changes as it uses on an oil change. I was kinda hoping the valve cover with the PCV valve in it would be the reason for that, so I bought the new improved cover. At the same time I bought new spark plugs so I could change those. When I was swapping them, I found one spark plug to be worn different. It had the tip burnt of and it was full off black residue. This spark plugs had 18000miles on them. Another thing I noticed when driving, was a noise from the engine. The noise is only there when the engine is under load. The sounded is like when you pinch a tin can rapidly.
I have added pictures of the spark plugs.
What could cause the spark plug to look like this?
What could be the reason for the tin can sound I hear?

HD

 

[Heldju]

Here you see the bad plug vs a new one.

 

[OR VietVet]

That is burning oil on that cylinder. The deposits show that. Do a compression test on that cylinder and any, both, cylinders to each side. Report back with compression readings. The noise you hear sounds like pinging from to low octane on your fuel you pump in to the tank. If you are running 85 octane, go to 87 and see if the noise disappears.

When you do the compression test and that one cylinder is lower than the others, as a matter of fact, do a complete compression test on all 8 cylinders with all plugs out, anyway-squirt a little oil in the low compression cylinder and if compression comes up, you have a rings problem. If it stays the same the problem is valve related, meaning likely valve guides and seals. If you pull the heads for that, do all 8 cylinders along with a valve job but be aware that with the 140k miles, the rings may go at any time later. When you increase compression in there with a valve job, that can cause more pressure on old rings. Does not happen every time but just be aware.

Do you see blue oil smoke at a cold start or when accel hard?

 

[Heldju]

Hi. At the moment I am running the engine on 95 RON ocatane.

I have done a comp test on all cylinder except on cylinder 8. It was hard to access.
All numbers looked equal except for cylinder number 5. It had slightly higher number.
The bad spark plug came from cylinder 3.
Another thing I noticed is that on the driver side spark plugs it looks like the threads have oil in them. On the passenger side they are all dry.

 

[79jasper]

After changing the plugs, is the noise still there?
The build-up on that plug could cause detonation, iirc.

Sent from my SM-N960U using Tapatalk

 

[OR VietVet]

The compression test looks good because: " If a factory value is not available you can estimate it by multiplying your intake pressure by your engine's compression ratio - for example a 2005 Silverado with a 5.3L V8 has a compression ratio of 9.9:1 - if you measure an intake pressure of 17 psi you can expect a cylinder pressure in the 170 psi range."

It's a shame you wussed out on #8 cylinder.

In this case I would suspect valve guides and seals as the culprit.

 

[79jasper]

I would have thought 8 would be easier than 7.

Sent from my SM-N960U using Tapatalk