Engine shake due to motor mounts?

Scott P · October 28, 2020

I've had a bit of an slightly noticeable engine shake for several months on my 2014 Sierra AT with the 5.3L. In July 2019, the AFM lifter was replaced on cylinder 1. In March of 20, the same problem popped up again and the full TSB solution was used to replace AFM lifters and spark plugs on that whole cylinder bank along with a new oil manifold, etc. All done under warranty (42,000 miles on the clock at that point). A bad plug on cylinder 3 was replaced a day later.

Ever since that point, the truck has had a minor shake/shudder at idle. It feels similar to, but "duller" than how it feels when a cylinder drops from AFM failure. I had the dealer look at it and both the service manager and tech took it for a drive. No engine codes or misses were detected. The tech and advisor both felt it was possibly the motor mounts. But, since they are not covered under the powertrain warranty and that "it would take a couple hours to diagnose", we didn't go any further. I've been driving the truck as is. It's noticeable mostly when coming up to a stop light or when the engine is warm.

How likely is it the motor mounts? Has anyone experienced this issue? A search of the site here didn't come up with anything. If It is something that can be replaced, how difficult is the job? Can I knock it out in the driveway?

silveradosid · October 28, 2020

doesnt look that bad of a job

Scott P · October 28, 2020

Thanks for that link. I swear I looked some time ago for one, but must have missed it. The whole removal of the starter motor part is a bit disappointing though.

James Dink · October 28, 2020

what does your truck idle at? My truck idled super low and shook, bumped 75 rpm and cant tell it's running now

mookdoc6 · October 28, 2020

4 hours ago, Scott P said:

I've had a bit of an slightly noticeable engine shake for several months on my 2014 Sierra AT with the 5.3L. In July 2019, the AFM lifter was replaced on cylinder 1. In March of 20, the same problem popped up again and the full TSB solution was used to replace AFM lifters and spark plugs on that whole cylinder bank along with a new oil manifold, etc. All done under warranty (42,000 miles on the clock at that point). A bad plug on cylinder 3 was replaced a day later.

Ever since that point, the truck has had a minor shake/shudder at idle. It feels similar to, but "duller" than how it feels when a cylinder drops from AFM failure. I had the dealer look at it and both the service manager and tech took it for a drive. No engine codes or misses were detected. The tech and advisor both felt it was possibly the motor mounts. But, since they are not covered under the powertrain warranty and that "it would take a couple hours to diagnose", we didn't go any further. I've been driving the truck as is. It's noticeable mostly when coming up to a stop light or when the engine is warm.

How likely is it the motor mounts? Has anyone experienced this issue? A search of the site here didn't come up with anything. If It is something that can be replaced, how difficult is the job? Can I knock it out in the driveway?

Your 2014 does have a different Hydraulic style motor mount than after 2016's.

I would replace both motor mounts and like previous post....the Idle Bump of minimum 50rpm's is needed on Hot Idle mapping...but 100rpm's is really what's needed imo. Then you will be all good!

Scott P · November 3, 2020

On 10/28/2020 at 9:26 AM, James ****** said:

what does your truck idle at? My truck idled super low and shook, bumped 75 rpm and cant tell it's running now

The truck idles around 500 rpm. When the shake occurs, it does move the needle a tiny bit. That is why I thought something was off after the lifter repair. I have no idea what that number was previous to the repair though, so I have nothing to compare it to. Unfortunately, I do not have access to a programmer/tuner or whatever it would take to bump that idle up.

steelerdude15 · November 12, 2020

James is on the money. It's a tuning issue. These trucks were made to be as fuel efficient as possible. The idle has to be bumped up a little bit to take care of the rough idle. I plan on doing this when my powertrain warranty expires.

Grumpy Bear · November 12, 2020

Once you've had an issue you become hypersensitive. Mine has had a low rpm shutter since new. Now have 131,000 on the clock and unless someone else says it, I never notice it. Bump the idle.

15 Z71 · November 12, 2020

8 hours ago, Grumpy Bear said:

Once you've had an issue you become hypersensitive. Mine has had a low rpm shutter since new. Now have 131,000 on the clock and unless someone else says it, I never notice it. Bump the idle.

131,000 miles nice. I'm at 68,000 on my 15 Sierra and so far so good. How has yours been? Any issues?

Grumpy Bear · November 12, 2020

2 hours ago, 15 Z71 said:

131,000 miles nice. I'm at 68,000 on my 15 Sierra and so far so good. How has yours been? Any issues?

Replaced the plastic starter shield last year and a pinion seal right after I got it. The shield warped and was 'ticking' on the ring gear. The pinion seal was a weeper. Might have lasted a lifetime but I hate a damp under side. That's it as far as repairs. Wear items, a set of tires at 125K and one set of wiper blades. I service the crap out of it and I drive it like I care about it. So lots of filters and fluids and tire balance and rotations, alignments, wash and wax........

And I have a laundry list of modifications.....Some for comfort, some for reliability, some for ease of maintenance..... I have a built thread that includes all these items.

It's been a gem.