Oil on spark plugs - misfiring p0300

[donjetman]

Your engine issue could be counterfeit spark plugs? Or clogged injector?

I may have recently encountered one of these. I have a 1951 Chevy pickup truck with a low mileage 5.3L engine out of a 2008 GM pickup. It only has 2200 miles since truck was completed 10 yrs ago.
Lately it started missing when under load and threw engine code P0308 (#8 mis-fire). Checked header tube temperature with IR temp gun. #8 was half the temp of the rest. I put in a good used spark plug, poured a 20 oz can of Seafoam into the gas tank that only had about 4 gals of fuel in it, and it was fixed. Eventually I changed the rest the spark plugs, and added 5 more gals of fuel. I have driven it 100+ miles, and its running perfect.
That #8 spark plug looks strange. It looks polished (silver) or one side of the porcelain? Here's some pics of both sides:

 

[FAUST]

What vehicle is this?

As far as I know, spark plugs don't go through the the valve cover on any Tahoe/Yukon etc, like they do on the hemi or a Nissan VQ etc.

That’s what I am learning. 99% of videos are smaller 4 cylinder engines.

This is a 2007 5.3 Tahoe.

 

[FAUST]

Top is the original (bad design) valve cover w/130k miles.
Bottom is new updated design.
View attachment 415030

Perfect - I’ll be checking this next weekend. I was able to find this yesterday. If this is the updated valve cover, I’ll be working to fine out of the injectors are the issue.

Some work ahead. I’ll report back once I’m through the work.

Thank you all!

 

[mikez71]

Your engine issue could be counterfeit spark plugs? Or clogged injector?

I may have recently encountered one of these. I have a 1951 Chevy pickup truck with a low mileage 5.3L engine out of a 2008 GM pickup. It only has 2200 miles since truck was completed 10 yrs ago.
Lately it started missing when under load and threw engine code P0308 (#8 mis-fire). Checked header tube temperature with IR temp gun. #8 was half the temp of the rest. I put in a good used spark plug, poured a 20 oz can of Seafoam into the gas tank that only had about 4 gals of fuel in it, and it was fixed. Eventually I changed the rest the spark plugs, and added 5 more gals of fuel. I have driven it 100+ miles, and its running perfect.
That #8 spark plug looks strange. It looks polished (silver) or one side of the porcelain? Here's some pics of both sides:

View attachment 415038

Is that a crack under the tip?

 

[donjetman]

Is that a crack under the tip?

?
Myself (old hobby mechanic) and a couple of pro mechanic friends of mine have looked at it and haven't a clue as to why, what, etc.

 

[Larryjb]

That’s what I am learning. 99% of videos are smaller 4 cylinder engines.

This is a 2007 5.3 Tahoe.

OK, good that is cleared up then. There is no such thing as a plug tube seal on these. The oil is on the threads for one of the reasons others have suggested here.

I'd try the simplest first: pop the PVC off from the valve cover to make sure there is suction while the vehicle is running. If there is no suction, you probably need to replace the PVC valve which is easy.

 

[donjetman]

OK, good that is cleared up then. There is no such thing as a plug tube seal on these. The oil is on the threads for one of the reasons others have suggested here.

I'd try the simplest first: pop the PVC off from the valve cover to make sure there is suction while the vehicle is running. If there is no suction, you probably need to replace the PVC valve which is easy.

On the 07 and later engine they don't have the ole PVC valve.
The complete valve cover is the PVC.

 

[Fless]

On the 07 and later engine they don't have the ole PVC valve.
The complete valve cover is the PVC.

On my '04 L59 I have no proof that my valve cover is OE, but there's no indication that it's not. The complete valve cover is the PCV, even back then.

 

[Rocket Man]

Some engines have rubber seals where the spark plug tube meets the valve cover. I thought this engine would have those to replace - I’m finding oil on the threads of the plugs.

Sorry my original response was not specific.

That’s a 4 banger item. There’s no plug tubes on any v8 ever made with the possible exception of a Chrysler hemi.

 

[Larryjb]

On the 07 and later engine they don't have the ole PVC valve.
The complete valve cover is the PVC.

There is still a hose that connects the valve cover to the intake. I'd pop that hose off and check for suction.