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V8 running on 4 cylinders?

V8 running on 4 cylinders?

Postby peteyg39 [OP] » Aug 01 2011, 2:44am

Hey everyone, i have a brand new 2011 sierra 5.3 and i love it but i have a little concern with on thing. When i use my information button and watch my instant fuel mileage. you can see whether im running on all 8 cylinders or when it cuts down to 4. Now when it goes down to 4 the truck runs like garbage, stays in like a high gear even at low speeds, and makes a rattling sound from the tranny, best thing i can compare it to is trying to drive a standard and leaving a stop in like 2nd or 3 gear. I understand its trying to save gas but it does it all the time and i have to really get on the gas to get it to downshift and be able to pull out of it. Is this normal? anyone having the same occurrence? thanks
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Re: V8 running on 4 cylinders!!!???

Postby EKinMN » Aug 01 2011, 3:00am

I have this on my 2010. I can tell a slight difference between V4 and V8, but not like what you are referring to. I've never had it stay in a higher gear. Sometimes it bogs down just a bit.

Couple things:
Mine seems to have gotten smoother since it's broken in. I now have about 10,000 miles on the truck.
If it REALLY bothers you, consider having the dealership re-flash your ECM. Maybe it's not set correctly, and giving you some issues?
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Re: V8 running on 4 cylinders!!!???

Postby AzDragonLord » Aug 01 2011, 11:59am

Have the dealer check it. I have AFM on my 2009 Sierra and I don't feel or hear any difference when it swithces modes.
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Re: V8 running on 4 cylinders!!!???

Postby StarsnBars » Aug 01 2011, 12:18pm

I have a slight feel but nothing like your reporting. Take it to the dealer and go driving with them. Shouldnt be how your describing,,
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Re: V8 running on 4 cylinders!!!???

Postby jfusco20 » Aug 01 2011, 1:39pm

I just bought a 2011 sierra and I have the exact same problem when it goes into the overdrive gear and shuts down to 4 cylinders at low speeds. I brought mine back to the dealer and they said it was normal because it is pulling all that weight on just 4 cylinders! I don't think that it feels right and ready to hand the keys back to the dealer. They also told me if they flash my ECM that I would lose about 8-10 miles per gallon!? I was also told that the banging and clanging that the tranny makes is completey normal?
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Re: V8 running on 4 cylinders?

Postby tdsierraz71 » Aug 01 2011, 2:46pm

I have a slight feel when it switches from 4 to 8 with my 2011 sierra. Its more noticeable sound wise now that I have a dumped super 40 on it. It also seems to stick in v4 mode much longer if I am driving in D with tow/haul mode on. I am hoping it will get smoother as it only has 4100 miles on it and needs to break in more. Mine is no where near what yours sounds like. I would bring yours to the dealership and go for a ride with the service manager and make sure they recognize the problem. And as for the tranny, IMO a $35,000 brand new truck should not be banging and clanking on a regular basis. Make them fix it.
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Re: V8 running on 4 cylinders?

Postby tech182 » Aug 02 2011, 4:27pm

My '11 Silverado is seamless. The only way I can tell it's switching from 8 to 4 or back is look at the display. Changes in road service and gusty winds will make it drop out. Touching the gas will also drop it out of V4. For me, I think mine drops out of V4 too easily, it never stays in it much. Doesn't seem to do much good. Also, it won't go into V4 at all above about 48 mph.
peteyg39, with what you're describing, I'd be back to the dealer and then on the phone and writing letters to GMC. (my opinion is worth what it cost.)
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Re: V8 running on 4 cylinders?

Postby jfusco20 » Aug 04 2011, 6:26pm

I brought my truck back to the dealer and they brought in a GM engineer person to look at my truck. He noticed that my camshaft pully was wobbling when running and that the rattling noise from the tranny is the torque converter! Actually it is the drivetrain that rattles! He told me that there is not update to be made to the truck or tranny at this time and doesn't know when GM plans on making one!! So I said I wanted to get rid of the truck, and the service manager tells me that since I have put about 2200 miles on the truck that could be an issue. Mind you that I brought the truck back with like 500 miles on it and complained about the rattling noise. Then I brought back at like 1200 miles and their tech said that there is nothing wroung with it. Now that I want to get rid of it they are giving some troubles. Don't know what to do because there is only one midnight blue metallic ccsb with a 6.2L. It doesn't shut down to 4 cylinders, but it also doesn't have the 20 inch clade wheels, the rear defrost or the home convience package like the one I have now! Any suggestions??
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Re: V8 running on 4 cylinders?

Postby srr2 » Aug 05 2011, 3:59pm

Wow. Camshaft pulley wobbling and torque converter rattling. And the GM rep thinks this is NORMAL?? Wow. Maybe I made a mistake buying one of these. If I were you, I'd go collar the owner of the dealership and tell him the nonsense the service department is handing you, and see if he thinks that a rattling torque converter is normal. Or, cut your losses there and go to another dealership and throw yourself on their mercy. I've tried this and it works, probably because they want to make the original dealer look bad.

I can tell you that my new Silverado 1500 with 5.3 AFM seamlessly switches from 4 to 8. It hangs in 4 cylinder mode pretty well on the highway at 60-70 MPH in O/D. Only when it hits an upgrade does it revert to 8. The lowest speed it has switched to 4 that I've noticed (and that's only by looking at the info display) was around 45-50 mph and with light throttle in O/D. If you didn't know anything about this mode switching and were just driving the truck normally, there's no way you'd ever suspect that the engine was shutting down half its cylinders.
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Re: V8 running on 4 cylinders?

Postby catpower » Aug 07 2011, 5:26pm

You guys really thing the t/c is rattling? Wow, thats crazy. I have an 06 Impala SS with afm, and it acts the same way my truck does. As an ex auto tech for Ford, I noticed when Im in 4 cyl mode, and give it enough throttle to make the "rattle" occur, it is not a rattle. Im quite positive of this. I think it is a simple spark knock. Im willing to bet that fuel or ignition timing is a little off, causing a spark knock, and thats all the problem is. But if you guys are so worried about the 4 cyl mode, doesnt someone make a tuner to turn it off?
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