Afm And Oil Consumption

[rodram]

well.... at 100,001 miles the first thing I would do is to have the AFM tuned-off, get the pistons, rings and lifters all cleaned up ... and then hope your oil consumption problems are gone!

[music]

I don't think the problem is purely related to AFM. Too many AFM 5.3's out there with high miles, and zero issues. Maybe it's the ring fit. I'm guessing that GM uses a "build to one tolerance" ring/cylinder spec, meaning that some fit tight, some loose, and some "just right". I'm guessing issues would be more prone on the "loose" fits. By "loose", I don't mean "poor", just at the inner spec on the ring and outer spec on the bore. I could be uttering hogwash, but there has to be a reason that some do this, but most don't.

 

AFM operation itself may indicate fit (?). AFM requires that the disabled cylinders hold the combustion gas, acting as a gas spring. If a vehicle has a hard time holding AFM mode, then maybe the rings aren't tight enough to do the job, and it's leaking down. I mention this, only because I read many times on here where "afm never stays on"... but mine stays on a *lot*. Just some thoughts...

[441G]

if you want to get rid of afm this is good reading - its for a 6.0 but the trucks should be about the same.

http://www.ls2.com/forums/showthread.php?t=659175

[chas0218]

Is the oil getting burnt in the combustion chamber or is it leaking? i would imagine that the plugs would start to become fowled after burning the amount of oil you guys are talking about. Is the oil disappearing down the valve stems or because of the rings?

[fbachman]

About 2500mi on mine sice last oil change. Still above the full mark (by a hair). Will check again in about 1000miles

 

43,000 miles on the clock.

 

LY2, 5.3l, Iron, non-flex-fuel, AFM turned off about 4000 miles ago, so AFM was active from birth thru about 39,000 miles.

[191185]

Does anyone think weather or not your engine will burn oil has anything to do with how the truck is driven ? For example if I always rev my engine out to 5K rpm's daily, should I expect my engine to start burning a quart every 1,000 miles eventually ?

 

Or do most people think that weather you baby your truck or beat on it has little or no effect on weather or not your engine will turn out to be an oil burner ??

 

Thanks

[mtiffinal]

musicPosted Today, 11:40 AM

 

 

Maybe it's the ring fit. I'm guessing that GM uses a "build to one tolerance" ring/cylinder spec, meaning that some fit tight, some loose, and some "just right". I'm guessing issues would be more prone on the "loose" fits. By "loose", I don't mean "poor", just at the inner spec on the ring and outer spec on the bore. I could be uttering hogwash, but there has to be a reason that some do this, but most don't.

 

I too suspect some of this as I have read something about it. Maybe not spending the time they used to to get the best fit, thus trying to cut costs as much as possible.

 

 

 

chas0218Posted Today, 01:50 PM

 

 

 

Is the oil getting burnt in the combustion chamber or is it leaking? i would imagine that the plugs would start to become fowled after burning the amount of oil you guys are talking about. Is the oil disappearing down the valve stems or because of the rings?

 

 

 

Oil is NOT leaking, but rather getting burnt as you mentioned. I have read in one of the TSB's about plugs being fouled.

 

 

 

 

 

191185Posted Today, 02:29 PM

 

 

Does anyone think weather or not your engine will burn oil has anything to do with how the truck is driven ? For example if I always rev my engine out to 5K rpm's daily, should I expect my engine to start burning a quart every 1,000 miles eventually ?

 

IMO, the reving of engine should not be a contributing factor, but other driving conditions will such as hwy vs city driving and towing.

 

Mine just went into the shop today to address the 3qt per 3400 miles I mentioned earlier in this thread. This will be the 2nd time that warranty work has been done for the same oil consumption problem. I will post more in a few days when I get the truck back to let all know what was done.

[98 Z71 SLT]

musicPosted Today, 11:40 AM

 

 

Maybe it's the ring fit. I'm guessing that GM uses a "build to one tolerance" ring/cylinder spec, meaning that some fit tight, some loose, and some "just right". I'm guessing issues would be more prone on the "loose" fits. By "loose", I don't mean "poor", just at the inner spec on the ring and outer spec on the bore. I could be uttering hogwash, but there has to be a reason that some do this, but most don't.

 

I too suspect some of this as I have read something about it. Maybe not spending the time they used to to get the best fit, thus trying to cut costs as much as possible.

 

 

 

chas0218Posted Today, 01:50 PM

 

 

 

Is the oil getting burnt in the combustion chamber or is it leaking? i would imagine that the plugs would start to become fowled after burning the amount of oil you guys are talking about. Is the oil disappearing down the valve stems or because of the rings?

 

 

 

Oil is NOT leaking, but rather getting burnt as you mentioned. I have read in one of the TSB's about plugs being fouled.

 

 

 

 

 

191185Posted Today, 02:29 PM

 

 

Does anyone think weather or not your engine will burn oil has anything to do with how the truck is driven ? For example if I always rev my engine out to 5K rpm's daily, should I expect my engine to start burning a quart every 1,000 miles eventually ?

 

IMO, the reving of engine should not be a contributing factor, but other driving conditions will such as hwy vs city driving and towing.

 

Mine just went into the shop today to address the 3qt per 3400 miles I mentioned earlier in this thread. This will be the 2nd time that warranty work has been done for the same oil consumption problem. I will post more in a few days when I get the truck back to let all know what was done.

 

 

 

Guys...the only real fix is pistons and rings.

 

All the other stuff is a band-aid

[RyanbabZ71]

Just curious are people with non-Silverado/Sierras experiencing this issue? I havent really heard to much from Tahoe/Suburban/Avalanche (does the impalal have afm?) owners. Coincidence???

[mdavidthomas]

Update to 2007 Chevrolet Suburban

 

Service writer called today and said the Cylinder number 1 rod was showing wear. Not sure if tech who replaced pistons and rings forgot to button something up or low oil caused wear over time. They called GM and they are replacing motor. Should get Suburban back tomorrow morning. I asked if all updates had been done to the new motor including the shroud around the oil pan pressure relief valve. They said yes. My concern is what happens in another ~60,000 miles.

 

Also a note to anyone. Just a thought, when the Active Fuel Management engages, it sends pressurized oil to the lifters that collapse to keep the valves from opening and closing. It looks as if the pressure that builds up as those particular cylinders are compressed would cause air to leak past the rings into the oil pan area pressurizing the oil pan. As the piston is driven back down on the power stroke or intake stroke, the cylinder could become a vacuum sucking air and oil past the rings into the combustion chamber. As wear increases, so does the amount of air/oil leaking past the rings. It looks to me as if you would want to keep the intake valve open on both the power and intake strokes compensating with the computer for the mass air flow rate. Turn off the spark and fuel to the deactivated cylinders when AFM is activated. Then on both compression strokes you would want to allow the exhaust valve to open to allow air to escape the cylinder in order to reduce any drag on the engine. The biggest problem I see is that when AFM is activated with the exhaust valve open during the compression and exhaust stroke it would cause the exhaust to lean out with the added extra air being pumped into the exhaust manifolds which would make closed loop fuel control difficult.

 

In my opinion, the best thing would be to scrap the ideal. I didn't buy my suburban to get 20 mpg anyway.

 

mdavidthomas

Matthews, NC

[pm26]

I am still amazed why people keep buying vehicles with AFM engines. The potential headaches are just not worth saving a few dollars in fuel. Instead of crossing my fingers and hoping I do not have a lemon, I simply stay away from them.

[hillbilly4u]

Went in yesterday for the second 1k consumption check. Has burned 1 qt. in 2 thousand miles. They handed me a paper from GM saying 1 qt. per 3k is acceptable and that I seem to be just a little over that. Don't think they're gonna do much right now unless it gets worse. I bought the truck from a Dodge dealer and the sales rep swore it was not AFM motor. Course thats his word against mine.

[4wd]

Update to 2007 Chevrolet Suburban

 

Service writer called today and said the Cylinder number 1 rod was showing wear. Not sure if tech who replaced pistons and rings forgot to button something up or low oil caused wear over time. They called GM and they are replacing motor. Should get Suburban back tomorrow morning. I asked if all updates had been done to the new motor including the shroud around the oil pan pressure relief valve. They said yes. My concern is what happens in another ~60,000 miles.

 

Also a note to anyone. Just a thought, when the Active Fuel Management engages, it sends pressurized oil to the lifters that collapse to keep the valves from opening and closing. It looks as if the pressure that builds up as those particular cylinders are compressed would cause air to leak past the rings into the oil pan area pressurizing the oil pan. As the piston is driven back down on the power stroke or intake stroke, the cylinder could become a vacuum sucking air and oil past the rings into the combustion chamber. As wear increases, so does the amount of air/oil leaking past the rings. It looks to me as if you would want to keep the intake valve open on both the power and intake strokes compensating with the computer for the mass air flow rate. Turn off the spark and fuel to the deactivated cylinders when AFM is activated. Then on both compression strokes you would want to allow the exhaust valve to open to allow air to escape the cylinder in order to reduce any drag on the engine. The biggest problem I see is that when AFM is activated with the exhaust valve open during the compression and exhaust stroke it would cause the exhaust to lean out with the added extra air being pumped into the exhaust manifolds which would make closed loop fuel control difficult.

 

In my opinion, the best thing would be to scrap the ideal. I didn't buy my suburban to get 20 mpg anyway.

 

mdavidthomas

Matthews, NC

 

So if I understood, disabling AFM is the best option to avoid the above scenario? , right??

[mdavidthomas]

Update to 2007 Chevrolet Suburban

 

Service writer called today and said the Cylinder number 1 rod was showing wear. Not sure if tech who replaced pistons and rings forgot to button something up or low oil caused wear over time. They called GM and they are replacing motor. Should get Suburban back tomorrow morning. I asked if all updates had been done to the new motor including the shroud around the oil pan pressure relief valve. They said yes. My concern is what happens in another ~60,000 miles.

 

Also a note to anyone. Just a thought, when the Active Fuel Management engages, it sends pressurized oil to the lifters that collapse to keep the valves from opening and closing. It looks as if the pressure that builds up as those particular cylinders are compressed would cause air to leak past the rings into the oil pan area pressurizing the oil pan. As the piston is driven back down on the power stroke or intake stroke, the cylinder could become a vacuum sucking air and oil past the rings into the combustion chamber. As wear increases, so does the amount of air/oil leaking past the rings. It looks to me as if you would want to keep the intake valve open on both the power and intake strokes compensating with the computer for the mass air flow rate. Turn off the spark and fuel to the deactivated cylinders when AFM is activated. Then on both compression strokes you would want to allow the exhaust valve to open to allow air to escape the cylinder in order to reduce any drag on the engine. The biggest problem I see is that when AFM is activated with the exhaust valve open during the compression and exhaust stroke it would cause the exhaust to lean out with the added extra air being pumped into the exhaust manifolds which would make closed loop fuel control difficult.

 

In my opinion, the best thing would be to scrap the ideal. I didn't buy my suburban to get 20 mpg anyway.

 

mdavidthomas

Matthews, NC

 

So if I understood, disabling AFM is the best option to avoid the above scenario? , right??

 

 

 

 

Please understand that my above comments were just thoughts about what might be happening causing the high oil consumption. In my personal opinon, I'm not confident that a baffle (umbrella) on a pressure relief check valve and some new piston rings will stop what is happening over time. So I feel that the motor that was put into my vehicle will have similar problems over time especially with the AFM active. If anyone is to blame here it is probably the EPA for driving stricter emissions and mileage out of vehicles manufacturers. One other thought, could you imagine what would happen if GM were to state that the AFM operation was the cause of the increase oil consumption and wear and that they needed to turn the AFM off on the vehicles? Everybody would be suing and standing inline for a new motor.

 

mdavidthomas

Matthews, NC

[mtiffinal]

(hillbilly4uPosted Yesterday, 11:35 PM)

Went in yesterday for the second 1k consumption check. Has burned 1 qt. in 2 thousand miles. They handed me a paper from GM saying 1 qt. per 3k is acceptable and that I seem to be just a little over that. Don't think they're gonna do much right now unless it gets worse. I bought the truck from a Dodge dealer and the sales rep swore it was not AFM motor. Course thats his word against mine.

 

Which paper did they give you? The one I have is #01-06-01-011F that states 1qt per 2000 miles. You can look at the RPO codes in the glove box and figure out if it has AFM. There's also a place to enter your VIN and it will tell everything the truck was built with, but I can't remember off hand where that's at.