By on August 8, 2012


Adam writes:

I have been on your site for a couple years now and don’t remember ever seeing this topic. Our issue is we have a 2007 Suburban with a 5.3 AFM (Active fuel management) motor that was burning 1 quart of oil per 600 miles.

We bought the truck with 65k miles on it, now has 75k miles on it. After doing much reading, I found this is a very common problem with 2007 and 2008 models with the 5.3 AFM. My dealer has been more than perfect on getting it “fixed”. They did not request any service docs, instead they just verified the problem by doing a oil consumption test. Once verified, they went straight to replacing all pistons, rebuilt one head, replaced intake, and replaced the valve covers. The truck has since had about 2k miles put on it and all seems well. The oil looks new, before it would be black within 5 miles.

My main concern now is it really fixed? Or is it just patched up for another 30k to 60k miles. (from what I read this is the typical mileage when the problem starts). My dealer told me they had a production run where intakes for non-afm motors were put on the early afm motors in error. This is the first I have heard of this, and cannot find much online about it. The main theory online is that when the AFM shuts off 4 cylinders, they cool, allow small amounts of oil to pass by the rings. Over time this gums the up and they lose their spring tension.

So any insight from you guys or the members would be great. Not sure if I should keep the truck or sell it.

PS: Sorry for any typo’s, did this while at work. Also hopefully this is a good discussion for your piston slap.

Sajeev Answers:

Very interesting!  I was not aware of this particular problem with the LS Motor…I mean, I knew about LS-series Piston Slap and my love of this motor made me name this column after it…

But I digress.  It sounds like the dealer did the right thing and replaced all the offending parts as per GM’s guidelines, so good for them.  But, I know, that’s cold comfort to you. And honestly, I know of nothing that can make you feel better.

Except the automotive aftermarket! Hooray for the aftermarket!  I suggest you turn off the AFM system and forget about ever running on 4 cylinders.  All you need is a computer reflash from just about any GM tune shop, and there are plenty to choose from.  Not only does this almost guarantee that AFM will be history, you get a free performance tune for multiple fuel octane levels, no more torque management, quicker transmission action, and far livelier performance.

Send your queries to [email protected] Spare no details and ask for a speedy resolution if you’re in a hurry.

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14 Comments on “Piston Slap: LSX-FTL???...”

  • avatar

    ” no more torque management, quicker transmission action, and far livelier performance”

    So I have a 2006 3.9L Impala that never wants to kick down – would a reflash fix this for me? How much does one typically pay for a reflash?

    To his problem: I didn’t understand how removing the AFM would eliminate the oil loss problem

    • 0 avatar

      I think Sajeev is assuming that the oil loss problem was indeed caused by the rings gumming up due to cylinder cooling while running in 4cyl mode as a result of the AFM operation. Eliminate AFM, eliminate cylinder cooling during operation (as they’ll all be firing all the time), and thus the oil loss problem should not return.

    • 0 avatar

      Correct, the hyperlinks presented suggest that running on 4 is the source of the problem.

      A reflash is a couple hundred bucks, I am sure some GM-savvy tuner can do the same for your Impala, ship you a controller and you download it. If it first they don’t succeed, they will email you a new tune until you’re happy.

  • avatar

    What happens to the fuel economoy going from the AFM to non-AFM? To be honest I didn’t even know GM brought back the 8-6-4 motor. I know Honda uses cylinder management in some of their v-6 motors. Do those have similar problems? My neighbors Odyssey with 100k miles hasn’t had a problem with it so far as I know.

    • 0 avatar

      It’s not 8-6-4 anymore, now it’s just 8-4. 10-4?

    • 0 avatar

      Probably doesn’t make a huge difference in mileage. Customers are too resistant to really aggressive fuel saving strategies – like transmissions that stay in as high a gear as possible as long as possible instead of downshifting the moment you breathe on the pedal, or CVTs that stay locked at the peak RPM for efficiency for a given situation and instead have to be programmed to mimic a conventional transmission. I imagine that a displacement on demand motor doesn’t spend nearly as much time in reduced cylinder mode as it could because people expect full torque at about 1/4 throttle pedal application and are afraid to push the pedal down to the floor.

    • 0 avatar

      Not all Odysseys have the variable displacement capability. That was offered only on trims above EX (i.e. you had to have leather and a sunroof to get variable displacement) from the time it was first offered through the 2010 model year. The 2011+ models I believe brought its offering down to the EX trim, meaning you had to go to the base model to bypass the variable displacement.

      The Odysseys that had the variable displacement I have heard had huge issues with the unique front engine mount required to quell the varying vibrations caused by 6 and 3 cylinder operation. Oddities have never been kind to their front engine mounts (I had to replace one on our MY2000) and the variable displacement just complicated the part.

      • 0 avatar

        All 2011+ Odysseys (current “lightning bolt” generation) have the same engine with Honda’s VCM – the only difference in powertrain among the different trim levels is the Touring and Touring Elite get the 6 speed trans instead of the 5 speed.

        The biggest issue with the VCM is the noise from it – Honda engineered noise cancellation into the current gen Ody (although they have done that for a while with Acura I believe). That being said, it operates pretty invisibly – slight vibration but have to really be paying close attention. I have a hard time hearing it.

    • 0 avatar

      Our company had a 2008 Honda Pilot for the past 4 years with the V6 with cylinder management, and it was quite bad on chewing its way through oil. The low oil warning light would blink on every 2-3,000kms or so. Our local Honda stealership told us that there was nothing to worry about, that ‘it was perfectly normal for a modern V6’ *cough* b*llocks *cough*.

    • 0 avatar

      I believe when the system debuted, GM was claiming something like 5-10% improvement in efficiency overall. As with any manufacturer claim, I would say there’s likelihood that this is optimistic, but YMMV.

      I can tell from quite a few personal miles put on 5.3 AFM-equipped Impala SSs, the mileage is pretty bad. 24 on straight, level, easy, highway cruising seemed to be an achievement. I’m sure the trucks are worse, as the same engine powering 1.5x the weight or more with twice the frontal area and possibly additional drag from AWD would seem to indicate these AFM engines in the trucks would spend infinitessimal amounts of time cutting off the “extra” 4 cylinders. The Impala just needed a gust of headwind or a breath on the accelerator pedal in even the most favoriable conditions to switch from 4 back to the normal 8 cylinder operation, in my experience.

  • avatar

    Adam, you have an essentially rebuilt (virtually new) engine and a very durable truck platform. If you disable the AFM to prevent the problem from reoccurring you should be able to drive this Suburban for years.

    Selling/trading it for a new Suburban would cost you $30k+ depending on the trade value; buying another used one just puts you back into an older engine with who knows what issues.

    Keep your Suburban and enjoy it.

  • avatar

    Does the AFM always deactivate the same bank? If so I can see how this could become a major issue due to uneven wear.

    Do other AFM systems (e.g. Honda 3.5 V6) alternate the cylinders that are deactivated?

    • 0 avatar
      Brian P

      Only four of the cylinders even have the capability of being shut down (special lifters of a different shape with dedicated oil passages to them), so yes, it’s always the same four cylinders being shut down. AFAIK the Honda V6 engines are the same way. So, for that matter, is the VW/Audi 1.4 TSI.

  • avatar
    Carlson Fan

    We have a 2007 Tahoe. Yes the oil consumption is due to the AFM but part of the fix, which should have been done to your ‘Burb, is to install an oil splash guard on the lower end of the engine. This fix should keep the problem from reoccurring and most likely was done to the 2009’s and on at the factory. They don’t have this problerm despite the fact that the engines are no different than the 07 & 08’s.

    The AFM is totally seamless on our Tahoe and it has zero affect on performance. Especially when towing where you really need. With the Tow-haul mode engaged and the transmission out of overtdrive it never activates. In fact I suspect that one of the reasons our oil consumption problem hasn’t been as bad as most I’ve read about is becasue that truck has done a fair amount of towing. And it is an excellent tow vehicle. But I could be wrong

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