Piston Slap: LSX-FTL???

by Sajeev Mehta

Updated: May 16th, 2014 Published: August 8th, 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 sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.

#5.3L #ActiveFuelManagement #CadillacV8-6-4 #ChevyTruck #OilConsumption #Sierra #Silverado #Suburban

Sajeev Mehta

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3 of 14 comments

Deaks2 on Aug 08, 2012

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?

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- Brian P on Aug 08, 2012
  
  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.
  
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Carlson Fan on Aug 08, 2012

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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