Misfire mystery?

[DB1337]

Hello guys, I am having a misfire on cylinder 5 that I can't seem to get away from at all.

The P0305 code is not making a light on the gauge (it's pending) but I can still scan for it and slightly feel it at idle.

Vehicle: 2014 Chevy Suburban (Vin "0").

What I tried:

• Moving the spark plug to a different cylinder (didn't do anything)
• Moving coil and boot to a different cylinder and replacing said coil/boot (didn't do anything)
• Replacing fuel injector (didn't do anything)
• Compression test (good compression)
• Head gasket leak test (no leak)

Other notes:
I replaced the head gasket some months ago, and one of the top small head bolts snapped due to a faulty torque wrench... I have yet to deal with it as my compression/head gasket are seemingly fine.

I pulled the spark plugs from cylinder 1 (left) and cylinder 5 (right). I did notice a small amount of oil on the last couple of threads of the cylinder 5 plug, could that mean something?

Any guidance is appreciated.

 

[Hey you]

Just an observation... but are the plug gaps correct? They look quite wide to me... but that could be the zoom pic!
Have you tried some fuel additive, I use that every couple of tanks to help keep the fuel system going.

 

[strutaeng]

Why was the head gasket replaced? So it's running with a missing small head bolt? Any work done to the head?

I've heard that when an engine starts burning enough oil (due to piston rings, for example), that can cause a misfire. But those plugs look kinda normal. No oil consumption issues? May be worth to do a leak down test.

 

[Fless]

I'd agree with @Hey you that the gaps seem excessive. The electrodes also look quite worn. How old (miles) are the plugs?

 

[DB1337]

Just an observation... but are the plug gaps correct? They look quite wide to me... but that could be the zoom pic!
Have you tried some fuel additive, I use that every couple of tanks to help keep the fuel system going.

They are 0.040, might just be the angle. I'll try the fuel additive. Thanks.

Why was the head gasket replaced? So it's running with a missing small head bolt? Any work done to the head?

I've heard that when an engine starts burning enough oil (due to piston rings, for example), that can cause a misfire. But those plugs look kinda normal. No oil consumption issues? May be worth to do a leak down test.

Long story short, the intake broke and sent stuff into the cylinders. Had to take the heads off to clean them out well. Heads were professionally machined. Replaced with OEM head gasket. Has good compression and doesn't fail the blue exhaust fluid test. No oil consumption either. I will try a leak down test, thanks.

I'd agree with @Hey you that the gaps seem excessive. The electrodes also look quite worn. How old (miles) are the plugs?

To be honest I'm not sure, and I'd agree with you on the wear, but the fact that the code won't leave cylinder 5 regardless of the plug that goes in makes me think it may not be the plug itself.

 

[DB1337]

Is there any way to confirm it's not a bad cam lobe without taking the heads off?

I plan on taking the valve covers off to check the lifters next.

 

[Fless]

Once you've looked at the valve action, it might be time to use a borescope to look at all the areas within the hole -- piston top, cylinder wall, valve condition, etc.

 

[DB1337]

Once you've looked at the valve action, it might be time to use a borescope to look at all the areas within the hole -- piston top, cylinder wall, valve condition, etc.

Yeah I will definitely be taking a look with a borescope after looking under the valve cover, I fear that the valve might be the problem as I'm really making no progress with the "usual" fixes for misfires.

 

[DB1337]

Update:

Took the valve cover off and inspected the push rods, something is definitely weird with the cylinder 5 intake push rod. It looks like it has this orange scratchy appearance on the end that is closest to the camshaft. I haven't been able to find anything about this online at all, no idea what this is. Anyone ever seen something like this?

Images push rod order (left to right): Intake 1, exhaust 1, intake 3, exhaust 3, intake 5, exhaust 5.

Another angle of the same ends:

 

[kbuskill]

Have you verified that you actually have spark on cylinder 5?

I don't mean swapping coils, wires, plugs. I mean have you actually stuck a spark tester or screwdriver in the end of the plug wire while the engine is running?

I ask because the short harness on the coil pack bracket, that goes between the coils and the main engine harness, has been known to cause misfires. You can swap coils all day long and still have a misfire on the same cylinder.

 

[DB1337]

Have you verified that you actually have spark on cylinder 5?

I don't mean swapping coils, wires, plugs. I mean have you actually stuck a spark tester or screwdriver in the end of the plug wire while the engine is running?

I ask because the short harness on the coil pack bracket, that goes between the coils and the main engine harness, has been known to cause misfires. You can swap coils all day long and still have a misfire on the same cylinder.

I used an inline tester and a noid light, it appeared to be functioning normally and consistent with the other cylinders.

 

[TonyTahoe2017]

I had a long term type of issue with misfires. Replaced sparkplugs etc. Here's the shop report on my 2017 Tahoe.
I'm on here learning about what's going on trying to determine if $9k is a rip off. Cylinder Head replacement, Head Gaskets and value stem seals. I apparently had 2 colors of things in my cylinder head that were essentially oil and coolant.

|Codes: -P0300 - Misfire detected. -P050D - Rough Idle. Cleared codes, monitored misfires through a scan tool, under load cylinders 1, 3, 4, 5, 6 were intermittently misfiring. Injectors and coil packs work good with no misfires. Checked spark plugs, porcelain look good. Recommend replacing all spark plug wires, as many of the wires have internal corrosion. After replacing the wires, the issue didn't go away. Noted that this vehicle has been in for this issue back in April, I looked up TSB's and there's a TSB for these exact codes (P0300 & P050D) saying the liners in the heads give out and leak coolant into the cylinders. Block test passed, but on a warm engine. Need to block test again after the engine fully cools down. Pulled out several spark plugs, put a bore scope into the cylinders and 3/3 cylinders that I've checked are all wet on the inside and the cylinder walls are glazey. Need to pressurize the cooling system and see if there's a leak once the engine is cool. Preferably need to leave the car over night. After pressurizing the cooling system over night, PSI dropped. Checked the cylinders in the morning, noticed valve stems leaking and coolant present in the cylinders. Recommend replacing cylinder heads, head gaskets and valve stem seals.|REPLACE - Ignition Wires