carboncow

I'm reading a lot about the 2007+ engines with Active Fuel Management and it seems "some" are plagued with concerns. Our 2004 was a great vehicle (5.3L) with no concerns...but we had to sell it.

I've had a lot of european cars and they all have their issues with engines but in that world most of those issues come in the early years and we often say if you are buying a good running high mileage engine you got the good one as the systemic failures often came early.

Does that apply for these Suburbans...were most AFM issues early on?
Are they rare as we all know you only read the complaints! But I'm sure many of you have been on here enough to know if it's systemic or exception.

thanks for any useful input.

PS. I know knowing the service history helps but the deal we found is great...was a auction vehicle and car fax doesn't show much data.

KChevy75

My understanding is the AFM issue is primarily with the aluminum block. Something to do with the RPMs at which the pressure relief valve opens differing between the aluminum and iron blocks. The problem will only get worse with more miles. My 5.3L LTS has the iron block and has 206K miles on it now and didn't start showing some oil consumption until maybe 150K miles. Last I checked the oil level was at 4,000 miles after I personally rebuilt the trans due to a broken sprag, installed the AFM bypass valve shield and performed the cylinder cleaning. I was down about 1 quart. Previously, I would have been down maybe 2 quarts at 4,000 miles.


I've always only used Mobil 1 Fully Synthetic in it with 6-8K miles between changes and I think that has a lot to do with helping reduce consumption.


If it's an aluminum block, I'd be wary.

carboncow

Thanks but how does one know with a 5.3L which is alum and which is iron? Is the difference between flex fuel models and not? I'll run the vin through a decoder to see if that tells me anything...but any suggestions?


Also, I thought I read the AFM can be disabled with a software update...does it require the valve fix/removal too?

EDIT: Decoder only gave me 5.3L V8 SFI FlexFuel with Active Fuel Management

KChevy75

I don't know how you'd tell without being able to inspect it in person. Aside from rust and the color and texture, if a magnet sticks to the block, it's iron. If not, it's Aluminum.

carboncow

Thanks...I'm sure there is some reason they do one over the other vs. random nature. So hopefully someone can chime in on how to tell and why they chose one over the other!

carboncow

OK, two minutes after I posted I may have found the answer...

1. it appears that the 2WD drive LT's have the iron block while the 4WD trucks have the aluminum block.

2. Look at the VIN# and if the 8th digit is a 3, you have the aluminum block, if it is a 0 it is iron.

If #2 is true this vehicle has AL as I suspect 98% of all modern Suburbans to be...

EDIT: The info I stated above only applies to the new Gen IV Flex Fuel engines, so GM states.

intheburbs

AFAIK, all 2007+ 5.3 GM motors have AFM - whether they're in pickups or SUVs.

And that is precisely the reason why my two 2007+ trucks don't have 5.3 motors.

carboncow

Did you buy them used and thus knew about the AFM issues or you simply took issue with the AFM system?

In your opinion from being these forums is it a systemic enough problem to say all 5.3L with the AFM will eventually have major issues at the hand of these poorly developed system?

intheburbs

Yes, both trucks were bought used, and I was just not willing to take the chance on getting a bad 5.3 motor, so I didn't even consider them.

There are plenty of folks on here, and other boards, that will tell you they have a 5.3 with 100k, 150k, and even 200k with no issues. I don't doubt that. But to me, it's a game of percentages. In my opinion, you have a greater chance at having a vehicle with engine issues if you buy a used 5.3. Buying used is always a risk - no need to make it worse by buying an AFM motor.

Let's say the general likelihood of getting a lemon when you buy used is 5%, assuming you've done your homework. I my opinion, if you buy a used 5.3 AFM truck, the likelihood of getting a lemon is now 15-20%. That's not a risk I'm willing to take when I'm buying a $20k-$25k truck.

Right or wrong, it is my belief that the GM AFM design is fundamentally flawed. I will never own an AFM truck. And yes, if that means in ten years I have to look at other brands, so be it.