I'm looking at a '08 GMC Sierra have questions ?

1. [b:654c4848f0][u:654c4848f0]It has a "J" in the 8 digit of Vin#... will this truck have the AFM 5.3 V4/V8 engine ?[/u:654c4848f0][/b:654c4848f0] I have info that indicates the "J" is a 6.0, but I'm pretty sure it's a 5.3. I'd rather not have the 6.0 and if it's a 5.3 AFM, it's an early one and I'd like to avoid that too.

2. Anything else I should check for ? I'm going to have a local mechanic check it out if I decide to take it to the next step. I expect things like ball joints, etc. to be starting to show wear.

3. What's the easiest way to find out what axle ratio it has ?

4. The "Fuel Economy" readout seams to be stuck at 11.2. Is there something that needs to be reset for this ?

It is a SL1 Z71 with ~114,000 miles, no rust, a couple minor paint scrapes, and only a small ding in the middle of the tail gate where it looks like some "oopsied" when hooking up a trailer. It looks nice and the wife likes it too.

I got a CarFax and it's had Oil Changed every 5,000 or so at the local dealer for the first 85,000 miles... no record for last 1.5 years. This type of vehicle is totally new to me. The only thing similar I've had was a '95 GMC Sierra.

Thanks in advance.

I own an 08 sierra work truck and it has the 4.8 with 47000 on it. I believe the reset for the fuel is to just hold down the trip odometer. As far as the rear end ratio it should be on the driver side door sticker. It is an Indiana state sticker as that is where most are put together. That 6.0 is a thirsty engine. my truck has the 3:73 and I get 17 mpg. Good luck.

(quoted from post at 05:17:43 03/31/15)
1. [b:68e801e7a7][u:68e801e7a7]It has a "J" in the 8 digit of Vin#... will this truck have the AFM 5.3 V4/V8 engine ?[/u:68e801e7a7][/b:68e801e7a7] I have info that indicates the "J" is a 6.0, but I'm pretty sure it's a 5.3. I'd rather not have the 6.0 and if it's a 5.3 AFM, it's an early one and I'd like to avoid that too.

2. Anything else I should check for ? I'm going to have a local mechanic check it out if I decide to take it to the next step. I expect things like ball joints, etc. to be starting to show wear.

3. What's the easiest way to find out what axle ratio it has ?

4. The "Fuel Economy" readout seams to be stuck at 11.2. Is there something that needs to be reset for this ?

It is a SL1 Z71 with ~114,000 miles, no rust, a couple minor paint scrapes, and only a small ding in the middle of the tail gate where it looks like some "oopsied" when hooking up a trailer. It looks nice and the wife likes it too.

I got a CarFax and it's had Oil Changed every 5,000 or so at the local dealer for the first 85,000 miles... no record for last 1.5 years. This type of vehicle is totally new to me. The only thing similar I've had was a '95 GMC Sierra.

Thanks in advance.

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5.3L SFI
ftp://safercar.gov/MfrMail/ORG3532.pdf

Apparently the 5.3 was available as an aluminum block or an iron block at that time. The J code engine is the iron block. RPO code LY5. I don't know where they keep the RPO code list on the GMT900 trucks, but on that list you can also find the code that tells you which rear end it has. The J code engine(LY5) appears to have Active Fuel Management. I think that's when it first came out, and it's a problem you don't want to have.
Rear End Codes.

I have had two 5.3s last was 09,Z71 liked it a lot. It would stay on 4 cylinder at about 40mph on country road pulling 9000+ trailer. It had the 6 speed and I think the ratio 3.55 in rear. A friend had one same as mine he had engine problems with his, GM replaced some of the engines and his was one. When I traded it for 2014 HD 6.0 the computer showed 16.9mpg average and a some of that was pulling the trailer. My HD with the 6.0, computer shows average of 12.3.

I have an 08 Silvearado Z71 xcab w/5.3 auto,have gotten 21mpg on trips. Only has 33k miles on it.

Had an 07 briefly. Really liked the truck except... I did not have the nicer DIC - Driver Information Center. Evidently by not having that you cannot program out things like automatic door lock and when the headlights come on, etc. Some minor things like that but they really got to me as they affected me daily with work - put markers in back seat, drive a couple hundred feet, get out to get the markers and the back doors were locked again. That got old for me real quick so my next one had the nicer information center. Just a heads up, nothing against the truck and a lot of other vehicles have the same issue.
Good Luck

I had a 08 GMC with 410 gears, I now have a 14 and like the 6 speed transmission, BIG improvement. If you got one with 6 speed you will be much happier.

If you are aquainted with anyone at a GM parts dept, you could just have them run the VIN, returning the engine used, transmission, axle ratio, etc..

There will be two different fuel economy displays on the driver information center (DIC). You select the display with the DIC buttons. If the average mpg is stuck on 11.2, that's probably normal and you can reset it with the DIC buttons. The instantaneous economy should never be "stuck".

If the vehicle has active fuel management, the instantaneous economy display will also have an indication which switches between "V8", "V6" and "V4".

AFM engines only switch between V4 and V8 mode, there is no V6 mode. I find those trucks annoying to drive when they switch to V4, the exhaust note sounds like crap. If I ever own one, I will use a tuner to shut the V4 off, I have had a customer tell me his gets about the same mileage anyway. AFM is just a marketing ploy.

Don't know anything about the Sierra, but a word of caution on the "bed height" if you plan on towing older fifth wheel trailers. I have the 08 Chevy 2500 HD with the 6.0. Great tow vehicle, but they have a really high bed height. Gives me a fit towing my fifth wheel trailers. It is tough to get an acceptable clearance from the rear of the bed and I have to tow with the nose up on the trailers. I understand this is not a problem with newer fifth wheel trailers which are built to compensate for the newer truck bed heights.

I have an 02 GMC with the 6.0, it is a 2500HD, has the 2" lift, which does make trailers a little tricky at times. I am not positive, but would guess, if the truck you are looking at is a 1500, it is almost definately the 5.3, if it is a 2500, most likely the 6.0. I really like the 6.0, plenty of power. My truck only has 90k on it, only use it when need to haul or pull something, too expensive to drive otherwise. Just had the cab corners and rockers replaced, it's heading in to get Krown Rust control sprayed next, hoping to get at least another 10 years out of it.

I had a 2007 GMC Sierra Denali with the 6.2 and the 6 speed. I loved the truck but had plenty of issues. The 6 speed in mine slammed from first to second unless you were driving it like you stole it. Went back to the dealer multiple times, multiple filters and fluid changes and it just never got better. Tow haul mode sucked as it would get stuck and not want to shift. You could red line the thing on flat ground going from 1-2 and 2-3. I always had to use the manual shifting option when in tow haul mode. At 115,000 miles the engine started to eat anitfreeze and have that sweet smell. Both head and intake gaskets were leaking. I bought the truck at 40,000 miles and always took good care of it so I felt I had lots of issues. I always performed the recommended regular maintenance per the owners manual, or had the dealer do it if I was not able to.

I now have a 2011 Chevy Silverado with the 5.3l with the active fuel management and do not like it. It has the jumping RPM's issue while at idle and has been back to the dealer many times with no luck finding a fix. The rear suspension is weak for pulling a trailer that is anything more than a jet-ski or a few snowmobiles even though mine has a 9,500 lb towing capacity. I added Timbren's as well as a small add a leaf to keep it from sagging and I do not tow anywhere near the capacity. I usually am around 6,500 lbs with the trailer and equipment I use.

(quoted from post at 09:04:23 03/31/15) Just had the cab corners and rockers replaced,

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Leo,
If you don't mind, what was the ball park on that cost? My '02 should really have the same done soon.

(quoted from post at 06:33:17 03/31/15) AFM engines only switch between V4 and V8 mode, there is no V6 mode. I find those trucks annoying to drive when they switch to V4, the exhaust note sounds like crap. If I ever own one, I will use a tuner to shut the V4 off, I have had a customer tell me his gets about the same mileage anyway. AFM is just a marketing ploy.

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Don't know about marketing ploy, but my wife's '07 GMC, not classic, can not feel change between v4 and v8. the exhaust has a very nice deep rumble. Truck has well over 100,000 miles, been to dealer once for a/c comp. under extended warranty.

J does indicate 5.3. Scroll down

https://service.gm.com/dealerworld/vincards/pdf/vincard08 06-01-09 r1.1.pdf