Low compression 5.3L gen IV Cylinder 7

[FamilyForce6]

Hi all,
My 2010 Tahoe started developing a random misfire related to cylinder 7. I went through the usual causes but couldn't track it down so I took into a shop. They stated that the cylinder had low compression, which came when they added a little oil to the top of the piston. Bad rings was there diagnosis. I was really surprised because I keep on my oil changes and only use Wix filters and full synthetic. After looking at the cost of replacement engines I'm shocked and saddened ($8-$9K with labor!)

In my research I came across a TSB that actually deals with this type of issue. It states that cylinder 1 and/or 7 can get overwhelmed with oil due to valve cover design (I replaced with the updated design about 3 months ago) or due to excess oil spray from the AFM pressure relief valve in the oil pan. Interestingly enough, I disabled AFM when I purchased the vehicle.

The TSB recommends trying to put a solvent/cleaner in the top of the cylinder and soak it for 2-3 hours in addition to installing a shield over the AFM valve (though it says the problem is likely only to happen w/ aluminum blocks and not my iron block).

Any recommendations on how to proceed? Should I try to install a shield over the AFM valve (or plug it completely as others have done)? I am going to try cleaning from the top of the cylinder, but any recommendations on the product they'd recommend using would be appreciated since GM doesn't manufacture their recommended product anymore.

Additional helpful info:
* 165,000 miles on the clock (purchased 5 years ago with 125,000 miles)
* AFM disable done almost immediately after purchasing
* Regular oil changes and maintenance. (full synthetic and wix filters)

Thanks community!

 

[Fless]

@donjetman has great info about this -- I think he has a thread documenting what he did (other than the one below).

Mystery Oil Loss - Where is the oil going? 2008 Yukon Denali

so details on this oil. are you filling it back up every time you find it a qt low? what if you don't fill it, will it come back up after a day of driving and be lower again in the morning? Other members have filled the kids can full and very short mileage until they replace the valve cover and...

www.tahoeyukonforum.com

 

[rdezs]

Before pulling the oil pan to deal with the shield over the oil pressure relief valve, I would 100% focus on getting those rings freed up. I would start with GM's recommendation, they've had some success with it. Then if necessary move on to try other products. Hopefully you get the compression back.

If successful, I would say move forward with an AFM delete. And plug that relief valve at that point.

On an AFM delete I did recently for my neighbor on a 2010 6.2, here's a photo of cylinder number 7.... Had a lot more carbon buildup than the rest, but no compression issue yet

His is a 2010, just under 200,000 miles, and at some point the TSBs were addressed with the updated valve cover and shield over the relief valve in the pan.

Total cost in parts was under $2,000, which included a lot of things to do while in there. New water pump, radiator, all hoses, serpentine belt kit, all new OEM sensors in sending units, machine shop work on the head, etc

 

[j91z28d1]

They stated that the cylinder had low compression, which came when they added a little oil to the top of the piston. Bad rings was there diagnosis.


I have questions. what exactly did they do?

 

[rdezs]

I assume from his post they did the standard diagnosis by adding oil to the cylinder and rechecking compression... And he's inquiring what the best course of action is to address it.
Bad rings doesn't necessarily mean they're broken and or missing, in an LS engine it often means the ring is stuck compressed into its groove often from carbon buildup. If his compression had not gone up, then it points to the head gasket or the head/valves.

A lot of people are fully capable of digging into the engine themselves, but lack the diagnostic techniques to figure out exactly what's wrong, and $200 for a shop to diagnose is often very convenient. Sometimes they get it wrong, but low compression of one cylinder isn't that difficult to get him pointed in the right direction.

 

[Marky Dissod]

@FamilyForce6
If it's worth the time / energy / money to install the shield over the AFM valve,
seems like it can't go wrong, even if you do plug it, as the concern is controlling directional oil spray.

More importantly, think you are looking for cleaners that contain Poly Ether Amines.
At the time of this writing, this list should work, but may need updating as time passes:
Red Line SI-1 Complete Fuel System Cleaner
Chevron Techron Concentrate Plus 01154100-5179P
Gumout Regane High Mileage Fuel System Cleaner
Gumout Regane Complete Fuel System Cleaner
Gumout All-In-One Complete Fuel System Cleaner
Lucas Oil 10512 Deep Clean Fuel System Cleaner
LubeGard Fuel System Booster

You did not mention if your 2010 Tahoe is 'FlexFuel compatible' or not.
If it is, and E85 is at least 20% cheaper than the fuel you typically use, then use E85; it burns cleaner.
Whether or not you can use E85, feel free to use any or all of the cleaners above.

You mentioned 'Regular oil changes and maintenance (full synthetic & Wix filters)',
without mentioning which full synthetic (is it a Group3 or Group4 synthetic?)
or how often you actually change the oil. Valvoline Restore & Protect 5W30 comes very highly recommended.

 

[j91z28d1]

I assume from his post they did the standard diagnosis by adding oil to the cylinder and rechecking compression... And he's inquiring what the best course of action is to address it.
Bad rings doesn't necessarily mean they're broken and or missing, in an LS engine it often means the ring is stuck compressed into its groove often from carbon buildup. If his compression had not gone up, then it points to the head gasket or the head/valves.

A lot of people are fully capable of digging into the engine themselves, but lack the diagnostic techniques to figure out exactly what's wrong, and $200 for a shop to diagnose is often very convenient. Sometimes they get it wrong, but low compression of one cylinder isn't that difficult to get him pointed in the right direction.

I trust no shop anywhere. so I'd would honestly be amazed if they went as far as actually doing a compression test, let alone add oil and redo it.


that's why I asked for details. like did they actually say they did that, or did he happen to see them do it.

 

[donjetman]

@FamilyForce6
The TSB you posted above has been revised or superseded twice with:
https://static.nhtsa.gov/odi/tsbs/2014/MC-10114272-9999.pdf

When I did the piston and combustion chamber soak in 2018 I used Gunk brand Motor Medic and I soaked mine for 2 days.
In 2018 at 130k miles the TSB immediately cured my oil consumption, and today at 200k miles it still doesn't need any makup oil between 5k mile oil change intervals.

 

[rdezs]

While the TSB's are an indicator that GM recognizes an issue, something tells me that if you change your oil before reaching the 50% of oil life left according to the meter, you're far less likely to have these issues in the long run. I don't have any hard data to back that up, just personal experience with a few different LS engines.... I never let mine go beyond 4500 miles even with synthetic. I think oil is cheap when taken into account the extended lifespan of an engine that receives frequent changes.