V4 to V6 shudder

14silverado4.3 · November 21, 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.

Any luck with them replacing parts?

Thomcat · November 21, 2016

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.

X2 Forget the post I'm getting old and forgetful - I addressed the post previously.......at least the saving grace is I have a similar answer!!!!

The Silverado is my 4th 5.3l V4/8 AFM and none have exhibited a transition vibration. When I saw they were migrating to a V4/6 I figured they were nuts, specifically because of an inherent balance problem. These engines may run great out of the box but isolation mounts and magnetic fluid mounts can only go so far before they fatigue and the imbalance between the two types of engine motion becomes apparent.

Problem is not the AFM concept but the balance difference between V4 and V6. The V6 is an inherently unbalanced weird animal whose sole original purpose was to jamb an engine with more than 4 cylinders into a transverse configuration on their front drive vehicles which like the V6 did not exist prior to the late 70s. No need to use a V6 in the old RWD vehicles because there is plenty of room for a an I6 or V8. (Traditional "I" engines I4, I5,I6,I8 do not have a balance problem because all cylinders are in the same plane whether vertical or slanted like the old 60s/70s Plymouths & '62 Pontiac Tempest.)

Aside from harmonics , the only inherently balanced "V" engines with cylinders banks at 90 degrees are those with an even number of opposing cylinders....i.e. having the same number of opposing cylinders on each bank on the power stroke V2, V4, V8, V12 etc. A V6 where 2 cylinders in one bank oppose 1 cylinder on the other bank on a power stroke requires kludges to restore balance like counter-balanced, counter-rotating cranks, 60 degree opposition of the banks to make it behave more like an I6, etc. Those engine kludges done to balance a V6 will work against the engine when in V4 operation so you have to resort to expensive active motor mounts with magnetic fluid, or complex motor mounts which will eventually fatigue and the inherent balance characteristics become more evident.

Tried out the Range AFM defeat device on my Avalanche V8s and they worked well, but with mountain driving the engines spend most of their time in V8 anyway, and the V8-V4 transition is balanced and unnoticable so didn't bother with it on the Silverado, BUT if I had V6/8 AFM I would stick one on full time and remove only occasionally to cycle the AFM lifters and AFM discharge valve.

Edited November 21, 2016 by Thomcat

Rick35 · November 22, 2016

The service manager said GM considers the condition to be normal. That is a bunch of crap. I'm going to try another dealer but I'm not hopeful.

GMC2015 · November 22, 2016

I read on another forum that the shudder could be fixed by clamping open the flapper valve in the exhaust. My 4.3 has a slight but noticeable shudder in v4-v6, so I'll do it when I have time.

fmblizz · November 25, 2016

Is it possible for this V6-V4 issue to get worse by driving the vehicle. My 2014 only has 18000 miles on it. I didn't really notice it until this past month and I feel the vibration is happening more and more.

Always around the 1200 RPM area.. I can even set the cruise control when I feel the shutter start and it will continue to shutter for a bit before finally kicking in the two dropped cylinders and going back into V6 mode.

I hope there is a quick fix because I'm not going to live with this situation on a $42,000 MSRP truck.

blizz

Rick35 · December 10, 2016

I first noticed the shudder around 11,000 miles so I don't if it is related to a break in period. I got an oil change at a different dealer last week and I asked the service guy if he knew anything different about the issue. He confirmed that GM considers this to be normal. He knows all too well as he has the same model and the same problem I do.

Rick35 · July 16, 2023

Its been several years and a lot of aggravation since my last post. I wanted to add a conclusion that I finally fixed the problem. As someone suggested way back in the posts I added a disabler and the problem is gone. My gas mileage is a little less but I don't feel the shudder as the engine stays in V6 all the time. I should have done this a long time ago!