Oil on spark plugs - misfiring p0300

[FAUST]

Misfires are caused by mostly by bad wires or bad coils. Swap out the coils on cylinders 2 and 7 to the other bank. If the miss fire follows the coils, that is your problem.

I have done this - the misfire is the same regardless of what coil is there. I have swapped the 2&7 with other non misfiring coils and they still register a misfire.

Wires and plugs are less than 6 months with under 10000 miles on em - they are ACDelco components.

I’m going to replace the valve cover and see if that helps.

 

[FAUST]

I was trying figure out if there were plug seals, from what I’m learning here, not a thing.

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.

 

[FAUST]

OP, what year is your vehicle? I seem to recall the change to the valve cover was made in 2006-2007, so you may already have the updated version.

Edit: probably worthwhile to check your PCV as well.

This is a 2007 - I can check the cover to see if it’s new version or not.

PCV? I’ve not checked this - I’ll research a bit to see what I can find.

 

[strutaeng]

This is a 2007 - I can check the cover to see if it’s new version or not.

PCV? I’ve not checked this - I’ll research a bit to see what I can find.

Here's a link that has some pictures. My 06 LQ4 has the valve cover with the little square opening. Not sure when they started installing them. I cleaned the valve covers of a similar LQ4, but can't recall if that one was different. Anyways, yours should be the revised design valve cover.

The PCV should rattle when you shake. Just unplug it and test it. It's only like $10, so it's pretty easy to replace it.

https://bobistheoilguy.com/forums/threads/gm-ls-engine-3rd-revision-valve-cover-install.251305/

 

[donjetman]

Fuel injector can cause misfires too.

 

[ivin74]

I have done this - the misfire is the same regardless of what coil is there. I have swapped the 2&7 with other non misfiring coils and they still register a misfire.

Wires and plugs are less than 6 months with under 10000 miles on em - they are ACDelco components.

I’m going to replace the valve cover and see if that helps.

Swap out injectors on 2&7 and report back. You might have 2 bad injectors.

 

[Larryjb]

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.

 

[donjetman]

This is a 2007 - I can check the cover to see if it’s new version or not.

PCV? I’ve not checked this - I’ll research a bit to see what I can find.

You probably don't have an ignition problem. How do I know? Checkout the thread I did: https://www.tahoeyukonforum.com/threads/sparkies-no-beno.108579/ As ugly as the plugs were, it ran perfect, and no codes.
My guess is you have a bad or clogged fuel injector.

Read this GM technical service bulletin (TSB) that applies to your tahoe:
https://f01.justanswer.com/ebrock63...il+Consumption,+MIL+ON,+Engine+Runs+Rough.pdf
The updated driverside valve cover is a must.

Oil on the threads of spark plugs is a must because a dis-similar metals (steel plugs and aluminum heads.

There aren't spark plug to valve cover seals on GM V8s.

 

[donjetman]

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

 

[donjetman]

You might want to put a large 20 oz can (or more) of SeaFoam in the gas tank. Stuff sometimes works miricles.
BG brand 44K fuel system cleaner is awesome too.