My 99 7.3 has had a vibration / shake in cab as you rev up while in park in neutral around 1000 RPM -1700 mostly. Around 1500-1600 is the worst. At idle it seems fine and what you would expect from a 7.3 but then as you give it higher idle, it starts shaking cab and you can physically see seats start shaking and it all feels rough. It also translates to a vibration while driving in those RPMS down the road...

It has new injectors, transmission/ torque converter, HPOP, exhaust and a whole lot more.......

Any thoughts?

 

Have repaired the same issue on older ambulances. Crankshaft and the rotating assembly is out of balance. Start by inspecting the balancer on the front of the crank. Look for any signs of the rubber coming out or of any movement. If so replace balancer. If not then be prepared to pull the engine to remove the crank and have it balanced.

 

Any idea if adding the aftermarket Fluidampr will or has done much to help?

 

Yes. Have installed a few and have noticed a significant change in vibration.

 

When you installed them, were ones being replaced in good shape or worn out? Meaning is it just that much better than stock or did it just need a new one?