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Checking for AFM issues. How?

mrsocks

Full Member
Joined
Jan 28, 2014
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I am going to look at an 08 Z71 (with 140k on it) and want to make sure I have the right things to look for in trying to determine if the AFM has caused any non-catastrophic issues and this is my plan:

1) Check the plugs on #1 & #7 against #3 and #8. All 4 should be the same if all things are fine. If plugs 1 & 7 are fouled (since 1,4,6,7 are the shut down cyls, right), there is an issue.

2) If the plugs were possibly changed, there could still be cyl wall or ring damage. So pressure testing cyls 1,4,6,7 against 2,3,5,8 should be able to show any issues as well. (pressure on a flex fuel should be lower as it's the alum engine as opposed to the iron / non-flex model, right?)

If these all pass and the engine is fine for now, I will turn off AFM and life should be good.

If I choose to leave AFM on, I should change the value cover and add the baffle and do a good cleaning of the cyl with the cleanser fluid.

Does this sound like a solid enough plan to give me a pretty reasonable idea of the condition of the engine?
I of course will not be able to test drive it long enough to monitor the oil use, so I am hoping that these checks will provide some good information.

I will continue my research and post followup info here as well.

Thanks.

 
I found this list of articles: http://easyautodiagnostics.com/index_gm_4.8L_5.3L_6.0L/index_of_articles_2.php

It includes how tos on checking pressure on the cylinders and for a blown head gasket.

The right side says it is for AVs up to 2006. Would the procedure be the same for 2007+ ? Is there something different in the way the engine would pressure test with the AFM?

 
Re: "If I choose to leave AFM on, I should change the value cover and add the baffle and do a good cleaning of the cyl with the cleanser fluid"

Plugs are probably your next best indicator.......if #1 & #7 show fouling, might be best to re-evaluate whether valve cover, AFM off and cleaning will rectify a potential oil burning issue. You have to consider that a compression test may not turn up a worn oil ring problem, the bottom oil ring which is designed to flex in it's seat with the tapered edge of the oil ring designed to scrape excess oil from the wall could be worn from being frozen in the seat while the upper compression rings which are designed to seal compression might still test OK.

If not already done the valve cover must be changed regardless of whether AFM is turned off or not to avoid a future problem......the cover drain hole and PCV valve takeoff is a separate oil burning related issue that must be addressed, photos in a referenced article below

Also if a dealer.....put him on the spot and ask for the name/number of the last owner on the title and contact them to ask about the oil burning and repair status regarding the oil baffle and valve cover replacement. Probably won't help but failure to provide it might prove a bargaining point for an extended warranty period to evaluate.

Found a link to the most recent GM mechanics article on this issue which might help in your decision


http://img.gogmpartswest.com/pdfs/Oil%20consumption.pdf







 
Thanks.
I had read through that as I was trying to formulate a plan.
Is there a way to tell externally if the cover has been changed, like a tab or something on it for the revised version?

If the cylinders were bad, wouldnt it idle rough too?
 
mrsocks said:
Thanks.
I had read through that as I was trying to formulate a plan.
Is there a way to tell externally if the cover has been changed, like a tab or something on it for the revised version?

If the cylinders were bad, wouldnt it idle rough too?


Looks like it is the same externally, identify only by internal exam for the drain hole location and part number.

A few bad oil control rings would not necessarily cause a rough idle if the compression rings on their pistons are still good. The lowest oil control ring flexes in its seat to scrape excess oil off the cylinder wall on the downward stroke and does not contribute much to compression.....that's the job of the multiple upper compression rings which are designed to form a tight seal on the cylinder wall to compress the mixture ......so if a few oil control rings are damaged but all the compression rings are still within spec it likely will not be picked up on a compression test.

Had one bad cylinder on my old 283.....valve guide seals were good, no oscillation in vacuum, so it had to be a stuck or broken oil control ring.....compression checks were fine in all cylinders and engine was as smooth as silk until that one cylinder fouled  the plug every 500 miles or sooner ....in the end used a Doering brand spark plug in that one cylinder specifically designed to fire in oil and after that the 283 would run great between the routine 10K spark plug changes. Don't know if they are still available but those Doerings were some plugs, ground lug was shaped like a ring and likely a different heat range to keep the spark going and it cleans itself.
 
Thomcat said:
Re: "If I choose to leave AFM on, I should change the value cover and add the baffle and do a good cleaning of the cyl with the cleanser fluid"

Plugs are probably your next best indicator.......if #1 & #7 show fouling, might be best to re-evaluate whether valve cover, AFM off and cleaning will rectify a potential oil burning issue. You have to consider that a compression test may not turn up a worn oil ring problem, the bottom oil ring which is designed to flex in it's seat with the tapered edge of the oil ring designed to scrape excess oil from the wall could be worn from being frozen in the seat while the upper compression rings which are designed to seal compression might still test OK.

If not already done the valve cover must be changed regardless of whether AFM is turned off or not to avoid a future problem......the cover drain hole and PCV valve takeoff is a separate oil burning related issue that must be addressed, photos in a referenced article below

Also if a dealer.....put him on the spot and ask for the name/number of the last owner on the title and contact them to ask about the oil burning and repair status regarding the oil baffle and valve cover replacement. Probably won't help but failure to provide it might prove a bargaining point for an extended warranty period to evaluate.

Found a link to the most recent GM mechanics article on this issue which might help in your decision


http://img.gogmpartswest.com/pdfs/Oil%20consumption.pdf


Any chance that tis article still exists somewhere....I couldn't open it thru any of the threads I found it in.....
 
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