Oil on spark plugs - misfiring p0300

[FAUST]

I have been trying to find a resolution to the random misfire code p0300.

When replacing plugs and wires - approx 3-4months ago - I noticed the threads were black, like oil was on them - I just thought of this while I was cleaning my garage and found the old plugs.

I cannot find a DIY process to replace the plug tube gaskets/seals. I am going to replace the valve cover gaskets, but want to do the plug tube seals too.

Any help is appreciated.

 

[ivin74]

The oil you see on the spark plugs are from the crankcase oil vapor. That's why most folks install an oil catch can on their vehicles.

I suggest you replace the drivers side valve cover with the new design. The original design let's to much oil into the air intake in which it is then burn thru the cylinders.

 

[FAUST]

The oil you see on the spark plugs are from the crankcase oil vapor. That's why most folks install an oil catch can on their vehicles.

I suggest you replace the drivers side valve cover with the new design. The original design let's to much oil into the air intake in which it is then burn thru the cylinders.

The entire valve cover? Or just the gaskets? I assume to cover as a whole. When you say new design, any aftermarket design or do you have a recommendation of where to get the new design valve cover?

This is helpful.

Also, oil catch? Where can I find this and where can I find a process to install?

Thank you!

 

[strutaeng]

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.

 

[FAUST]

The entire valve cover? Or just the gaskets? I assume to cover as a whole. When you say new design, any aftermarket design or do you have a recommendation of where to get the new design valve cover?

This is helpful.

Also, oil catch? Where can I find this and where can I find a process to install?

Thank you!

Never mind - I found the answer to the questions above!

This has been super helpful. Thanks again for the quick response!

Is it possible this has been causing misfires - I see misfiring on cylinders 2 and 7. Occasionally the others but not regularly.

 

[ivin74]

Never mind - I found the answer to the questions above!

This has been super helpful. Thanks again for the quick response!

Is it possible this has been causing misfires - I see misfiring on cylinders 2 and 7. Occasionally the others but not regularly.

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.

 

[Fless]

What is a plug tube seal on one of these engines?

 

[Foggy]

What is a plug tube seal on one of these engines?

NON Existent

 

[Fless]

I was asking the OP since he mentioned them.

 

[FAUST]

What is a plug tube seal on one of these engines?

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

 

[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.