Would pulling a vacuum on the PCV side of the crankcase restore lost power from worn rings?

[WeekenderNutJob]

My 2008 GMC Yukon XL Denali (6.2L AWD) has 250K miles and has blowby and presumably worn rings and burns oil. I have read good things about "engine restore" additives, but not ready for that yet. I replaced the valley pan gasket this weekend and the intake had about 1/2 a cup of oil in it when flippled over. Seemed like a lot to me..... So, I purchased an amazon catch can to try and keep it from going through the PCV and back into the intake...but I was thinking...

If I capped off the intake return side of the PCV tube and instead pulled a vacuum on the crankcase side (either an electronic vacuum pump or tie into another "non essencial" vacuum source - i.e. not the brake booster) would the increased vacuum on the crankcase cause the piston rings to "suck" or fit better to the cylinder walls an restore power? It's my understanding that there is no real PCV ball valve on my car, just some baffling in the valve cover (known to be problematic in some models which have an "upgraded" part from GM). To improve this idea, I could keep the catch can before the vacuum source and instead, just pull the vacuum on the "out" side of the catch.

The reason I ask is my other car (E46 BMW) has an entire forum on this topic called the o2 pilot mod and pulling a vacuum on the top side of the crankcase caused my oil consumption to drop to almost nothing and a noticeable power increase, and that was almost 100K miles ago. In my BMW I went from a quart every 1000 miles, to almost nothing between 7500-mile changes. Can it be done on this car also?

TLDR Question: So on my Yukon could I tie into a large vacuum line, or create one with an electronic vacuum pump potentially, and pull a vacuum on the PCV port of the crankcase to help restore lost power and decrease blow-by in worn rings by basically "sucking" the rings back to the cylinder walls? What is wrong with this idea?

P.S.: Please don't roast me please if it's a dumb idea on this car for some reason vs a functioning idea on my other car.

 

[wjburken]

I think you’d be time and money ahead by installing the improved valve cover and keep your catch can in place between the PCV port and the intake.

I may not be understanding what you said correctly, but I’m pretty sure the intake manifold is the only vacuum source on your vehicle so not sure what other “non-essential” vacuum source you’d use. Just to be clear, the brake booster doesn’t create vacuum, but instead uses vacuum created by the intake.

In my opinion, the oil in your intake has almost nothing to do with worn rings and more than a little to do with the PCV port design on your valve cover. The improved design definitely helps with keeping oil out of your intake and oil consumption. A catch can is the final line of defense in keeping oil out of your intake, but won’t help with oil consumption.

Lastly, I don’t see how increased vacuum on the crankcase would have any impact on how the rings fit inside the cylinder resulting in more compression and less blow-by. A little more explanation of how your theory works would be interesting to read.

Have you verified worn rings? Do you have confirmed loss of compression in your cylinders by doing a compression test?

 

[drakon543]

i'm also somewhat confused. so the top side of your crankcase is your valve covers. i would like to suggest staying as far away from comparing a gm product to a bmw. those cars are just an engineering nightmare with a ton of stuff that equally mind blowing as a wtf moment. so the problem is the crankcase isnt venting fast enough so the valve covers mentioned above from @wjburken should solve part of that problem. some catch cans can be purchased to varying levels including one that doesn't vent back to the intake. so plenty of options there the more crank venting you can the better. those additives are a bandaid so keep that in mind its not a magic one shot deal that rebuilds the worn the metal. not sure what grade of oil your using but i would also recommend going one grade thicker. the big one question to ask is if your oil has a slight gas smell when you change it. if it has a fuel smell then its definitely your rings if it doesn't it really might just need better venting.

 

[Foggy]

I use a belt driven vacuum pump on my supercharged small block chevy with
methanol and nitrous....
the vacuum pump does help blowby and helps to seal the rings better. Plus it
keeps all the BS out of the engine by evacuating it...
With that being said, My ring gaps are built/made for Forced Induction and therefore
are quite a bit wider than a stock/naturally aspirated set up.
I believe you are chasing something that just cant' be cured... but the symptoms
can be helped some by doing what's suggested above:
Install the updated valve cover and install a good catch can correctly : this will help
tremendously

 

[iamdub]

My 2008 GMC Yukon XL Denali (6.2L AWD) has 250K miles and has blowby and presumably worn rings and burns oil. I have read good things about "engine restore" additives, but not ready for that yet. I replaced the valley pan gasket this weekend and the intake had about 1/2 a cup of oil in it when flippled over. Seemed like a lot to me..... So, I purchased an amazon catch can to try and keep it from going through the PCV and back into the intake...but I was thinking...

If I capped off the intake return side of the PCV tube and instead pulled a vacuum on the crankcase side (either an electronic vacuum pump or tie into another "non essencial" vacuum source - i.e. not the brake booster) would the increased vacuum on the crankcase cause the piston rings to "suck" or fit better to the cylinder walls an restore power? It's my understanding that there is no real PCV ball valve on my car, just some baffling in the valve cover (known to be problematic in some models which have an "upgraded" part from GM). To improve this idea, I could keep the catch can before the vacuum source and instead, just pull the vacuum on the "out" side of the catch.

The reason I ask is my other car (E46 BMW) has an entire forum on this topic called the o2 pilot mod and pulling a vacuum on the top side of the crankcase caused my oil consumption to drop to almost nothing and a noticeable power increase, and that was almost 100K miles ago. In my BMW I went from a quart every 1000 miles, to almost nothing between 7500-mile changes. Can it be done on this car also?

TLDR Question: So on my Yukon could I tie into a large vacuum line, or create one with an electronic vacuum pump potentially, and pull a vacuum on the PCV port of the crankcase to help restore lost power and decrease blow-by in worn rings by basically "sucking" the rings back to the cylinder walls? What is wrong with this idea?

P.S.: Please don't roast me please if it's a dumb idea on this car for some reason vs a functioning idea on my other car.

You can try it if you're so inclined. But, before adding complexity, I'd first rule out the common root causes and ensure the rings are clean and not stuck, particularly on #7 and maybe #8. Basically, I'm saying to clean and heal the wound before just covering it with a fancy bandaid. @donjetman has a very pertinent story for you.

 

[WeekenderNutJob]

You can try it if you're so inclined. But, before adding complexity, I'd first rule out the common root causes and ensure the rings are clean and not stuck, particularly on #7 and maybe #8. Basically, I'm saying to clean and heal the wound before just covering it with a fancy bandaid. @donjetman has a very pertinent story for you.

Thanks for the info. Found another thread with the TBS and updated part numbers for the valve covers. I am the 3 or 4th owner so don't know if it's already been updated so I guess I have to find the part numbers before I tear it apart.

As for the reasons for my thoughts of pulling a vacuum on crankcase for those that were asking: https://inthegaragemedia.com/horsepower-from-nothing/

 

[wjburken]

Thanks for the info. Found another thread with the TBS and updated part numbers for the valve covers. I am the 3 or 4th owner so don't know if it's already been updated so I guess I have to find the part numbers before I tear it apart.

As for the reasons for my thoughts of pulling a vacuum on crankcase for those that were asking: https://inthegaragemedia.com/horsepower-from-nothing/

You said the vacuum would decrease blow-by.

decrease blow-by

I’m reading this article, it says that it helps evacuate the buildup of pressure caused by the blow-by. The theory makes a little more sense now. Thanks for sharing.

 

[iamdub]

Thanks for the info. Found another thread with the TBS and updated part numbers for the valve covers. I am the 3 or 4th owner so don't know if it's already been updated so I guess I have to find the part numbers before I tear it apart.

As for the reasons for my thoughts of pulling a vacuum on crankcase for those that were asking: https://inthegaragemedia.com/horsepower-from-nothing/

I can never find his thread so I tagged him in. He took his 6.2 from consuming a considerable amount of oil to essentially nothing by performing the TSBs. He used a cheaper, but apparently equally (or more) effective solvent than the GM stuff. Not saying you don't have excessive wear. But, there's a chance that your 250K-mile engine might be in better shape than it appears.

 

[donjetman]

Do the new improved valve cover, GM# 12570427 (for 07-08), and a piston/combustion chamber soak (TSB# 10-06-01-008M).

https://f01.justanswer.com/ebrock63...il+Consumption,+MIL+ON,+Engine+Runs+Rough.pdf

In the fall of 2018 our new to us 130k mile Yukon Denali w/6.2 was leaking and burning 2oz of oil every 100 miles. First, I installed a cheap chicom catch can. It was catching 1 oz per 100 miles. In other words, 1 oz of oil per 100 miles was making its way into the combustion chambers. So, all the rings were stuck because of the defective original valve cover that was allowing all that oil to be sucked it the combustion chambers. For the soak I use a product made by Gunk called "Motor Medic", and my soak lasted 36 hrs, unlike the TSB.

The other 1 oz per 100 miles was getting/leaking by the rear main crankshaft oil seal.

I did the TechnicalServiceBbulletin (link above) and changed my rear main seal. Oil consumption went to near zero. Today, almost 5 yrs later it has 190k miles and consumes 1/2 qt per 5000 miles.

https://www.tahoeyukonforum.com/threads/rear-main-seal-job-pan-etc-07-yukon-denali-6-2.108334/

 

[donjetman]

My race car (in my signature here) had a normally aspirated 1170 hp bbc chevy and a Moroso belt driven vacuum pump. It is common knowledge in drag race circles/engines that hp gains are considerable with a good vacuum system setup.