Misfire help

[chadbt2014]

I have a 2019 Yukon XL SLT with 5.3L and 4x4 and 115,000 miles. I had noticed on a trip to Colorado that there was some sluggishness or "mild kicking" when accelerating in the 1000-1500 rpm range. Especially in higher gears. No codes though. On our ride home, it was worse and finally threw a P0301 code. My local mechanic told me that it sounded like a coil issue. I am assuming he ran more detailed diagnostics than my code reader. He replaced the coil and spark plugs. Ran better for about a day. Then started doing the same thing again. Finally gave me a P0308 and P066D code. I don't want to take it back to the mechanic until I have a better idea of what may be the problem. If coil 1 was bad, why is coil 8 bad now? I don't think its the coils. My code reader recommends either intake manifold gaskets or a fuel injector. Could the P06DD code be the real issue? The original P0301 code was with old oil. New problems are with both old and new oil. Any help would be great. Thanks.

 

[chadbt2014]

I swapped the #8 coil with another cylinder, erased the codes and drove it again. It's throwing the same P0308 code with the swapped coil. So my instinct about the coil seems to be verified. Any insight on this would be great.

 

[Tahoeticker]

Do a compression Check on the cylinder. Move the plugs and wires to another cylinder to rule them out.

 

[alpha_omega]

How long have you been running the new oil? Are the intake gaskets you’re referring to original?

First thing I would do (in the event you didn’t have a bi-directional scan tool) would be finding answers to the following:

Have you checked the spark plugs?

Have you checked the wires and their connectors (for the fuel injectors and coils)?

Have you checked the torque specs on the intake manifold and ensured all of the connection points for the engine are properly sealed (give things the wiggle check, making sure nothing is loose). There may be a small vacuum leak somewhere.

Have you cleaned the MAF (mass air flow) sensor?

 

[chadbt2014]

To answer a few of the questions above. My mechanic changed the spark plugs when he replace the #1 cylinder coil. So I think they should probably be ruled out.
There are only maybe 200 miles since the oil change.

I assume that they put the same plug wires in their original location when they replaced the spark plugs. Maybe somehow #1 wire got moved to #8. I'll ask the mechanic.

I have not checked the manifold bolt torque and the MAF has not been cleaned

Intake gaskets are original

When I was swapping the coils yesterday, I noticed some oil inside the L-shaped piece that you have to remove and the front of the cylinders to get the coil cover off. It attached to the engine right in front of the first cylinder on each side and then to the air intake. Is that supposed to be there? Oil level is within range.

Any feedback on the P06DD code?

I can replicate the misfire scenario when needed now.

 

[Hmj7819]

I have a 2019 Yukon XL SLT with 5.3L and 4x4 and 115,000 miles. I had noticed on a trip to Colorado that there was some sluggishness or "mild kicking" when accelerating in the 1000-1500 rpm range. Especially in higher gears. No codes though. On our ride home, it was worse and finally threw a P0301 code. My local mechanic told me that it sounded like a coil issue. I am assuming he ran more detailed diagnostics than my code reader. He replaced the coil and spark plugs. Ran better for about a day. Then started doing the same thing again. Finally gave me a P0308 and P066D code. I don't want to take it back to the mechanic until I have a better idea of what may be the problem. If coil 1 was bad, why is coil 8 bad now? I don't think its the coils. My code reader recommends either intake manifold gaskets or a fuel injector. Could the P06DD code be the real issue? The original P0301 code was with old oil. New problems are with both old and new oil. Any help would be great. Thanks.

I have a 2007 Tahoe with the 5.3L. I just did a head gasket replacement and am having a misfire issue on cylinder 1 and 8 now myself. I have replaced coil packs, plugs, wires, new fuel injectors and lifters. I have fuel loading up in my cylinders though and for some reason am not getting spark to them.

 

[Fless]

I have a 2007 Tahoe with the 5.3L. I just did a head gasket replacement and am having a misfire issue on cylinder 1 and 8 now myself. I have replaced coil packs, plugs, wires, new fuel injectors and lifters. I have fuel loading up in my cylinders though and for some reason am not getting spark to them.

See the main post below for details. Comments here will scatter responses on different threads.

Misfire after head gasket replacement

Hello! I have a 2007 chevy tahoe 5.3L Z71. I recently replaced the head gasket, coil packs,spark plugs and wires. I upgraded to a cold air intake also. Now when I start it it stuggles to turn over and has a significant misfire on cylinder 1 and 8. I switched out the coil packs, plugs and...

www.tahoeyukonforum.com

 

[TonyTahoe2017]

I have similar issues. I'm told it's Cylinder Heads. coolant and oil getting into cylinder heads or whatever. Mine is 2017. But had this issue for quite a while.

|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

 

[Oshkash]

I just seen a video on YouTube. There's a mechanic out of Florida, and he loves diagnosing misfires, and one of the things that he found is the cracked porcelain on a spark plug, even if it's a hairline, will cause it to misfire.