2014 isx vibration

[race7820000]

ok, so I bought a 2014 579 pete a month ago with a isx motor.10spd

when I test drove it I noticed it had a very slight vibration when accelerating and I assumed it was because I was bobtailing and truck was sitting for a few months.

when you hook up to a trailer (empty) the vibration gets worse. when the trailer is loaded and you apply a lot of torque like going up a hill the dash will vibrate almost like a washboard. (1250-1350rpm) but when it doesthat and you let up on throttle even a little bit then it goes away.

The vibration is worse when motor is under a load, but if you let off the throttle it goes away. it only does it when your accelerating.

I have taken it to peterbilt,kenworth and cummins

I have had the ride height, u joints,rear end, carrier bearing etc etc checked 3 times.All good

had truck aligned also and installed new tires , virgins , thinking it would help...it did not

Cummins put the truck on a dyno and recreated the vibration

They did all the engine performance tests with the fuel inject,pressure etc etc. all of them passed

They said motor sounds goofy like its detonating, they changed accuator and accuator housing because they thought it was dumping to much fuel.

Finnally they gave up and said they think vibration is in motor but they don't know what it is without tearing it apart.

today I noticed the davco fuel filter looked like it needed changed because it was full, but when they did the dyno test a cpl days ago the fuel level was at the bottom, I changed it anyways and no difference.



I am hoping someone else has had this problem because im about ready to light a match and walk away....slowly lol

thanks