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Been watching this forum for years seeing how folks are liking their sierra and dealing with the dreaded oil consumption issues and occasional mis-fires. I believe I have both solved, for me at least, after turning off AFM and wanted to share the results. Some background:

Truck:2011 Sierra Crew Cab All terrain, purchased used in Feb 2012 with 10K miles on it. Always taken to a local, family owned GMC dealer for service.

~60K - first experience with mis-fires, took to dealer who confirmed mis-fires on cylinder 1, called it a bad coil and it was replaced. Also suggested a full tune up (plugs etc) which I did.

~80K - noticed oil pressure was starting to read low, dip stick showed no oil, added 3 qts before it again showed as full. This did not resolve the low oil pressure and eventually the check engine light came on. Did an oil change myself and this resolved the low oil pressure. Dirty filter? obstruction? EVIC showd 30% oil life remaining.

82K - second mis-fire experience, took to dealer who indicated cylinder 7 this time. Bad coil again they said, replaced. At this point I had the new head cover put on as well that GM adjusted to address oil consumption in these motors.

Now I'm continually checking oil level, adding as needed, at this point was not recording miles and oil needed yet as I was informed oil consumption is normal.

98k - third experience with mis-fire, cylinder 1 which I confirmed via a reader before visiting the service center. Dealer said bad coil, I challenged them as we had just changed it. They pulled the plugs and 1 was completely fouled, in his words it looked horrible. They hypothesized the plugs had fouled before they put the new baffled head cover in. They replaced all plugs free of charge.

105K - mis-fire again. At this point I now have my own code reader (plug for Dash Command app, nice to be able to read codes quickly) and see it's cylinder 7. pull the plug and it's fouled, replace and truck runs great.

112K - another experience with low oil pressure, changed oil and filter, followed by a mis-fire (cylinder 1) and plug replacement. I now begin adding oil frequently and monitoring results.

115k - .5 qt low
115.7K - .5 qt low
116.6K - .5 qt low

So now I'm in a pattern of continually monitoring oil level, which, some times is fine but for the most part I'm adding every 1,000 miles and I drive alot so that's frequent. Constantly "feeling" for a mis-fire, hoping it doesn't happen on a long trip and also keeping 4 plugs in the truck at all times. Finally, not letting the oil life get under 40% for fear the oil is clogging something.

It all hit a head this summer when from 120k-130K I replaced plugs 1 and 7 twice, they were only lasting about a month. What I didn't realize but do now, they fouled faster after long highway trips rather than after long towing trips or extended local driving around home.

After another mis-fire in November, I ordered the Diablo InTune i2 and installed the 87 octane tune and de-activated AFM. I replaced all plugs and topped off the oil. After 4K miles, towing and extended highway trips, I've checked the plug twice in cylinder 1 and it looks brand new. My oil level has stayed constant as well with a marginal drop from full but still well high on the dip stick. Mileage is not noticeably different, I'm still trying to gauge that more accurately but still 430-450 miles per tank and on those long trips the range goes over 500 which is what I was doing before.

The attached picture shows plug conditions before and after AFM de-activation. All plugs are from cylinder #1, the two at the far right are from this summer, I'd say about 2 months apart. 3rd from the right is at the beginning of November, in fact it's from the day I ordered the Diablo because I was so fed up with changing plugs and having no confidence in my truck I pulled the trigger right away rather than wait for a sale. 4th from the right is the plug just before I turned off AFM, only about 500 miles on it and you can see it's already getting black. Far left is the cylinder 1 plug after 1K miles, looks brand new.

I'll try to keep you all posted on what happens from here but I'm feeling good about oil level staying the same and plugs staying clean. I'm not worrying as much before taking long trips either.

IMG_2932.JPG
 

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So, in a nut shell, turning off the AFM has seemingly solved or at least greatly lessened the oil consumption and fouled #1 and #7 plug issues????

Glad to hear that and please keep the updates coming. It might give some hope and peace of mind to many others.
 

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Discussion Starter · #5 ·
esox07 said:
So, in a nut shell, turning off the AFM has seemingly solved or at least greatly lessened the oil consumption and fouled #1 and #7 plug issues????

Glad to hear that and please keep the updates coming. It might give some hope and peace of mind to many others.
correct, no noticeable oil consumption after 4k miles AND no fouled plugs on #1 and #7, the two driver side cylinders that shut down in V4 mode and the two cylinders I would say most owners have issues with.
 

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Very nice. Glad the problem seems to be resolved for you. Others are not so lucky.
 

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Is it 1 2 7 and 8 that shut down? I need to pull mine and see what they look like, as I get that shuddering on medium acceleration as well. Cleaned my throttle body the other day and that cleared my CEL but it still comes on every now and then for a half a day or so.

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Discussion Starter · #9 ·
esox07 said:
I believe they are 1, 4, 6 and 7.
correct...

Cylinder Deactivation (Active Fuel Management) System Description
System Operation
General Motors Active Fuel Management engine control system has the ability, under certain light load driving conditions, to provide maximum fuel economy by deactivating 4 of the engines 8 cylinders. The engine will normally operate on 8 cylinders in V8 mode during starting, idling, and medium or heavy throttle conditions. When commanded ON, the engine control module (ECM) will direct the active fuel management system and deactivate cylinders 1 and 7 on the left bank and cylinders 4 and 6 on the right bank, forcing V4 mode. Refer to Lubrication Description and Cylinder Deactivation (Active Fuel Management) System Description.
 

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Yah, it is a very interesting concept, and while it is light years ahead of the 1980's introduction of the system, it still has a long ways to go and in reality, it only provides significant fuel savings under perfect conditions. Typical driving habits and conditions will lead to minimal if any actual fuel savings for most people. If you drive 55-60 on flat roads without many stops and no loads, you will see real fuel savings. In town, with a load, or faster highway speeds and you won't notice much in savings. But, it all looks good on paper and helps GM meet the CAFE standards set up by the EPA.
 

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Discussion Starter · #12 ·
Still going strong. No Misfires, oil consumption is not gone but is now what I'd consider normal in that at each 6K oil change it is a bit low, previously it would have been bone dry.

I did start getting some knock/ping running the diablo sport 87 octane tune with 87 Octane gas, stepped up to 89 octane at the pump and no more pinging. This may be due to alot of carbon in the cylinders, will see if some seafoam helps but I'm not too worried about it right now.

will keep checking back in every couple months.
 
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