V4 to V6 shudder

Rick35 · October 17, 2015

It worked! Now that you see this thing you could do it yourself with a few scraped knuckles. If you could get the part, that is.

Rick35 · October 17, 2015

Thanks to everyone who shared their experiences. Hopefully this can now help you get your trucks running smoothly.

Edited October 17, 2015 by Rick35

Rick35 · October 18, 2015

I've had a chance to do some straight highway driving this weekend and unfortunately some of the shudder still exists. I think I notice it now because the road is smooth and also because I'm looking for it. If I didn't know it was a problem I don't know if it would bother me. I need to talk to service on Monday as a follow up and will see what they think. I may have to live with it. But it is much better. Maybe I'll hook a small bungie onto the clamp and see if that helps. It may help put a little tension on the pipe to take up what vibration remains.

Rick35 · November 8, 2015

Its been a few weeks since my last posting and I figured I needed to provide an update. My vibration/shudder issue still exists although it is slightly better. I scheduled another appointment with my dealer thinking they could add another dampener. Service called and told me the one dampener is the only fix for the problem so I cancelled the appointment and asked for guidance in how to initiate a buy-back. The guidance received was an 800 number. I found a GM warrranty/lemon web page and sent an email to GM and am waiting for a reply.

There are a number of concerns or unknowns about this condition with few facts:

1. V4 to V6 shudder appears to be unique to 4.6L engine. I could not find any posts where the issue occurs on V8's.

2. Bulletin from Oct 2014 talks to AFM vibration issue and addresses exhaust mounts and bolts

3. Exhaust vibration has been happening for years on many vehicles and various dampeners have been used to counteract vibration and to reduce noise.

4. Dampener used in my situation was employed two years after model year was introduced. It was described as a new fix for the problem. Why now? It took two years to come up with a resolution (that doesn't work)?

5. My issue surfaced at 10-11,000 miles - no issue prior to then. Why now?

6. There is no information on what is causing the issue although GM is holding to its vibration dampening solution.

My issue is that I don't know what is going on in the engine. My plan was to run the truck for ten years and now I don't know if that will be possible. I don't know what I'm experiencing is causing any damage to the engine and I believe I need to get out of the vehicle now while it is in otherwise great condition. Hopefully GM will help me do it.

tstodda · November 9, 2015

I would call GM directly and hopefully you get some good news.

My opinion on the problem, based on owning one and lots of research:

A V6 is not as balanced as a V8...and now turning cylinders on and off you are making matters worse (I would bet, on a less noticeable scale, that even the 5.3 shakes in transition). All of the fixes involve tightening and dampening...not trying to eliminate the root cause of the shudder.

My opinion on the solution:

Disable AFM on the 4.3.

Rick35 · November 10, 2015

_{I talked to GM today. First I received an email saying that my email was received and I would hear from a senior advisor within 24 hours and then I received a call late this afternoon. Most of the discussion was about me explaining what the problem was and ended with the advisor asking me what I wanted to do. I added that I was not the only one to experience the problem based on exchanges with other owners (on this forum) and this should not be a surprise for GM. The advisor was going to have a discussion with the dealership and we're going to talk again later this week.}

Edited November 10, 2015 by Rick35

2doorpost · November 12, 2015

Just road tested a new 2015 Sierra that has the V6 setup (double cab). Sure enough, at 50 mph , she started to shudder. Needless to say, the test drive ended soon after that and I came home in my old ride.

You'd think these folks would get their act together already.

Jake4090 · February 21, 2016

I was told by my dealership that I have to change my driving style because I like to tap the gas on the interstate. BS. If you are still having this problem and do not care if you have the AFM, Range technologies has an AFM bypass. Plug and play. Slightly less gas mileage, but no shudder and no drone. It acts like an additional mod bus and cancels out the AFM. It leaves your truck in full time v6 mode. It does not over-write the computer. It takes ten seconds to install and is awesome to not have the shudder or vibration.

2doorpost · March 1, 2016

I bought a '15 Silverado that was identically equipped to the Sierra that I road tested and walked away from . No shudder on the Silverado.

If it starts doing it, I'll disable the AFM.

Conclusion · March 1, 2016

_{I talked to GM today. First I received an email saying that my email was received and I would hear from a senior advisor within 24 hours and then I received a call late this afternoon. Most of the discussion was about me explaining what the problem was and ended with the advisor asking me what I wanted to do. I added that I was not the only one to experience the problem based on exchanges with other owners (on this forum) and this should not be a surprise for GM. The advisor was going to have a discussion with the dealership and we're going to talk again later this week.}

Any updates on your situation, been a few months wondering what the outcome was?

Rick35 · March 9, 2016

GM offered $5000 trade-in assistance to be used on a new purchase. I had to make a deal with sales including the tradein of my 2014 Silverado. They didnt offer me enough to make it worthwhile. If I did buy a new truck I would have had to take out a new loan which would mean an extension of 18 months which equates to about $9000. And that included the trade in assistance. On top of that I didnt want an 8 cylider and looked at a Colorado. I traded in a Colorado and forgot how small it was. And there were no deals. So I decided I liked my truck more than the other options and decided to keep it.

Edited March 11, 2016 by Rick35

Rick35 · July 12, 2016

Its been a few months since my last post and I wanted to let people know that my shudder problem is worse. Its especially noticeable around 35mph but I also get it at highway speeds. I'm heading back to the shop to see if there any new ideas about fixing the shudder. Since GM didn't offer enough money to help a trade I'm going to recommend that they start replacing parts starting with the exhaust system. The service manager mentioned it early on and I didn't take him up on the idea.

Rick35 · July 12, 2016

And I should add that the service writer I deal with says that I'm the only one of his customers with this issue.

Thomcat · July 12, 2016

I wonder if it is a harmonic balance (well imbalance) in the engine? Starting combustion on two cylinders could be whats causing this. A V6 is more harmonically balanced than a V4, even though this is a V6, you still have to account for a lack of combustion. Do you notice it more when you mash the gas or when it transitions to go up a hill or something?

I think it you may have it right with respect the cause being due to harmonic imbalance between the two states, but not so much the increase in combustion kinetics otherwise all V4/6 and all V4/8 would experience the shudder caused by a power surge and they do not. And, a V6 configuration is definitely not more balanced than a V4. Inherently harmonically balanced "V" engines are those with equal numbers of opposed pistons in each bank, i.e. V4, V8, V12, etc. as are all "I" or flat (pancake) engines I4, I6, I8, I10 etc. The "V" engines with unequal numbers of opposed pistons in each bank must rely upon kludges such as counterweighting on the main crank, or a system of counter rotating auxiliary crankshafts. The amount of counterbalancing necessary being determined by the angle of the banks, i.e. 90 or 60 degrees. So as the V4/8 AFM engines do not have a harmonic vibration related to balancing consideration the V4/6 AFM arrangement may which would be noticeable in the V4 to V6 transition.

Besides, other than cooling concerns for the middle cylinders on an I6, the only real advantages of a V6 to an I6 is length of the engine so it can be jammed into the width of front wheel drive transverse mounted configurations and the height of larger displacement engines permit lower hood lines.

Rick35 · July 18, 2016

I have had discussions with my service people a couple of times about possible engine problems and they really believe the issue is in the exhaust. I was in getting an oil change on Friday and told them I wanted to start replacing parts. I want to start with the exhaust and maybe end up with the engine. They can't fix the problem but they want me to believe its not the engine or that the shudder isn't causing engine wear. I'm not buying it. Priority is vacation and I'll reconnect with them when I return.