Last post on Nov 26, 2013 at 5:54 PM
You are in the Chevrolet Silverado & GMC Sierra
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GMC Sierra 1500, Chevrolet Silverado 1500, Fuel System, Truck
#301 of 415 Re: 08 GMC Sierra AFM problems [raldo]
Oct 30, 2012 (8:11 am)
If you were planning on working with a GM dealership to get this checked into, we're available to check in on this with them. Please contact us via email at socialmediagm.com with more information (including your name and contact information, a brief summary of the situation, the last 8 of your VIN and mileage, and the name of your dealership).
Sarah, GM Customer Service
#302 of 415 2008 "Certified" used GMC Sierra
Dec 13, 2012 (11:16 am)
I wish I had done a little more research before I purchased this 2008 GMC Sierra. It doesn't have the display that shows when active fuel management is working, so I didn't think it had it. Unfortunately after doing a little research, I found out that it indeed does have it since it is a 5.3. It is also flex fuel compatable (E85). I have only had the truck for less than a month. I purchased it Certified Used from Serra of Jackson, TN with 50k miles and one owner before me. I noticed no problems on the test drive, or the drive home into Mississippi. When I got home, I noticed a slight tick that sounds like lifter tick. I wasn't overly concerned with that. When the weather got cold for the first time, the tick was much more pronounced when the vehicle was first started, but it would go away in literally seconds.
I knew I had real trouble when I put 87 octane in it. The truck started to spark knock pretty bad at light throttle. Assuming I might have gotten bad gas (bought it at Shell), I put some Heet in the tank. This did nothing. I ran that tank of gas and put two bottles of Techron in at next fill up, and I filled up with 89 octane (Pilot). Slight improvement. The next tank was 87 Pilot octane with 2 bottles of Techron. The truck will spark knock like mad at light throttle at about 45 mph. It seems to me that it's spark knocking the entire time it's in V4 mode. Salesman at Serra told me to "put some Techron in it". I told him I already did and that it didn't help, but no check engine light had come on and would I be wasting my time taking it in for service. He said he'd ask and call me back. I never heard from him again. I took it to a local dealer and complained and left it with them. The tech that drove it heard nothing, and the service manager said that some AFM noise was normal. I tried to believe him because I like the truck, but the spark knock is annoying and is most likely damaging the engine. So, I return to the dealership and drive it with the same tech inside. I keep him in there until it spark knocks like hell and ask if he hears that. He says he didn't hear anything other than exhaust noise. Whatever, everyone else that rides with me in the truck can hear it, and no exhaust noise sounds like spark knock. If it was exhaust noise, it would be more rythmic than it is. Finally, to prove it was spark knock, I filled up with 93 octane. Spark knock almost completely gone. If it was exhaust noise, it would remain the same. I went to the dealership and asked about trading it in on a new 2012 model, and they had one left. I test drove it, and it sounded nearly as bad as mine. I'm certain it is spark knock, and I'm certain the reason it is happening is because the timing is a little off due to weak opening / closing AFM valves during V4. The dealership was nice enough, and sort of eventually admitted to hearing something, but said half of the vehicles with AFM do it and it wasn't worth tearing down the engine and replacing valves, because GM wouldn't pay for it anyway if the offending valves and lifters weren't too far out of spec.
So after a little research and thought, I'm convinced it is indeed spark knock, being cause by bad valves or lifters (which there is a TSB about). I'm also convinced the dealerships have to say they don't hear it or it isn't a problem because GM isn't going to reimburse them for any work unless it's really bad. GM, in order to save money, doesn't believe in repairing something to prevent catastrophic disaster, only repairing the disaster after it happens. So I've got $24k or so in a "certified" (yeah, right) used vehicle that I hate to drive now. I suppose I can put some more 93 octane in it and run it for a while. That'll eat up whatever cost savings I might've gotten with AFM. I considered having the AFM shut off. But, what I'm most inclined to do is fill it with 93 octane and trade it in on a Ford. I know all vehicles have their problems, but I had a 98 Dodge that I loved and always heard the rumors of weak transmissions. I babied that truck and changed trans fluid every 50k miles, only to have it fail twice at 130k and 170k. I sold it with 190k because it still didn't shift gears right. I don't want to try and put Mobil 1 every 3k miles in this truck and run 93 octane to try to avoid the innevitable AFM valve failure. I guess if there's enough rumors of problems with a particular vehicle, they're probably true to some extent. And the AFM rumors are pretty rampant. I know all AFM engines aren't bad, but why would I want to gamble on another?
Sorry for the rant. Not 100 percent sure what my best course of action is to be honest. To sum up, 53k miles now, and I've had it for a month. 10k miles or 11 months on the warranty. It spark knocks like hell on 87 octane, especially in V4 (shouldn't do that if it'll supposedly run on E85), and GM dealer says they can't hear anything abnormal. No CEL....yet. Any advice appreciated. Or I will sell it to you at a great discount if you live in the area.
#303 of 415 Re: 2008 "Certified" used GMC Sierra [jswain2]
Dec 13, 2012 (3:43 pm)
You have a 100K power train warranty. Drive until it blows up and you should get a new motor. Document all your visits to the dealer.
#304 of 415 Re: 2008 "Certified" used GMC Sierra [jswain2]
Dec 14, 2012 (7:43 am)
One thing we can do is document that you're having this concern and follow up with your dealership on this for you. Please email us at socialmediagm.com with more information (including your name and contact information, the last 8 digits of your VIN and mileage, the name of your dealership, and a brief summary of the situation).
GM Customer Service
#305 of 415 Re: 2008 "Certified" used GMC Sierra [chuck1]
Dec 14, 2012 (2:06 pm)
It's a 2008. The powertrain warranty is up 5 years after it's initially sold. Which is now. I have 11 months on the remaining "certified used" warranty. Factory warranty is expired. Have been documenting visits to dealer, though, thanks.
#306 of 415 Re: 2008 "Certified" used GMC Sierra [gmcustsvc]
Dec 14, 2012 (2:17 pm)
Will do, thanks. I called the dealership where I initially bought the vehicle again yesterday. The salesman was nice enough. He got the service manager to call me back today. The service manager seems to think it may be being caused by carbon build up, which is feasible. I'm going to try some carbon cleaner on the engine as he recommended and go from there. I'm hopeful, but a little doubtful that will resolve it, since the engine only has 52 or 53k miles. I have already used 4 bottles of Chevron Techron in the gas....I assume it would clean carbon deposits, but am unsure. Going to try something a little more aggressive and see what happens. If it doesn't work, I'll either get the dealership to fix it under warranty or trade even for a like vehicle at that dealership. Otherwise, I'll put some 93 octane in it and trade it for a Ford or Toyota. Not saying they're better vehicles, I'm just not real wild about the AFM and I don't think they have it.
#307 of 415 Re: 2008 "Certified" used GMC Sierra [jswain2]
Dec 15, 2012 (7:45 am)
Sorry to hear of your lifter troubles. At least your engine still functions. My advice is to trade it in on the Ford truck you've been considering while you can still realize some value. Once the general public comes to realize Chevy's AFM design is flawed, and that GM will not help outside of warranty, you can expect the value of used GM trucks to diminish - considerably. Right now, there is limited knowledge of the situation, noting that you were unaware when making your purchase.
Best of luck & happy holidays.
#308 of 415 2008 Silverado 5.3 AFM
Dec 17, 2012 (4:14 pm)
Just had to have my engine pulled for lifter and camshaft replacement. 118k. I know, Iknow...it is out of warranty. CS told me that like 1,000 times. Bottom line is this....in no way should a chevy truck need to have engine pulled this prematurely. Dealer mechanics say it is NOT a normal wear and tear issue, it is NOT a lack of proper maintenance issue, but it IS an engine design issue. While Chevrolet likes to pat themselves on the back by helping with some of the cost of the repair, I was still left with paying for the majority of the repair....even though it is a design flaw. I have purchased Chevy trucks brand new since I was 24 (able to buy one on my own) since 1995 and bought one every 4-5 years. My dad was a die hard Chevy fan since his first purchase in 1957. NEVER again for me. They turned their back on me and therefore I am turning my back on them as well. I am sure they are not loosing sleep about it, but it is what it is. I will be making sure that everyone I know in the vehicle market will know the specifics of my experience and everything that I learned about this "Design Flaw" before they make a purchase.
#309 of 415 Re: 2008 Silverado 5.3 AFM [churchy25]
Dec 17, 2012 (4:46 pm)
How about other 08's like yours where there are not any wide spread issues? (They have not been posted).
Don't know how many trucks GM sold with the 5.3 in '08-but it had to be at least 30,000 units, probably closer to over 40,000 units.
#310 of 415 Re: 2008 Silverado 5.3 AFM [churchy25]
Dec 17, 2012 (5:01 pm)
I had a problem with the 2011 Silverado I bought new. From day one, the AFM wouldn't work at highway speed (70 MPH). I tried and tried to get them to fix it. They even acknowleged that there was some sort of drag on the engine that was keeping it from changing into v4 at hwy speed. Bottom line is, GM told me they were not going to do anything about it and I could do with it whatever I wanted to. My only way out was to sue or sell the truck. I traded it in on another vehicle about two months ago. It goes without saying, I didn't trade for another GM vehicle. I couldn't get GM to stand behind it. I felt like I couldn't trust them any more. I only had 12,000 miles on it? The mileage I was getting was 14 city 15 cith/hwy combined 16 highway only.