I'm dealing with a vibration issue under acceleration. It starts around 1200-1300rpm. It happens while driving when I've got my foot on the gas. To eliminate tire balance and/or driveline issues, I tried it with the van in park as well. It's still happening. If I rev very slowly from 600 (idle), it starts vibrating around the same 1200-1300rpm. The vibration is fast and gets faster the higher past 1300rpm I go. It will almost go away completely around 2000rpm. Any ideas?

 

any misfire or knock codes?

How are your motor mounts?

 

No codes. Everything runs/performs fine.

I haven’t checked the motor mounts yet - what’s the best way to check them?

After some research I’ve begun to suspect the harmonic balancer. Is this a possibility?

 

I have seen old harmonic balancers where the outer ring slipped and rotated. if it is an externally balanced engine that would for sure give it a vibration.

What engine? What year?

 

I looked at it and on visual inspection, nothing appears to be out of order. I don't really know what the damage is supposed to look like however.

It's a 2013, 6.0.

 

That would be a L96 engine. Shouldn't be externally balanced and shouldn't be old enough for the rubber bond to fail. Still wouldn't be a bad idea to mark the inside and outside to make sure they don't move.

While you were there you might want to pull the belt off and see how all of the accessories spin. Something that happens at a certain engine RPM might also be one of the accessories.

 

It has an external harmonic balancer that looks like every other one I've seen. When I look up the new part on RA, it shows exactly what I have. I will try marking it to make sure it's not moving.

As far as accessories go, I just (<2000k miles) replaced: water pump, power steering pump, belt tensioner, idler pulley, serpentine belt, and AC belt. All are brand new, top-tier GM/AC Delco. The belt, tensioner, and idler are top-tier gates. The only things that didn't get replaced were the AC compressor, alternator, and crank pulley. I checked all those things when I had it all apart and they all felt ok, granted things can change at any time however. If the engine mounts were going bad, could they cause such a fine vibration?