ENGINE VIBRATION AT 1,200 TO 1,500 RPM

I have a 2006 crew cab short bed Duramax truck. While the truck is sitting with the transmission in park or neutral and accelerating through the rev range from idle to 5,000 rpm, the truck produces a distinct vibration from 1,200 to 1,500 rpm. The vibration is not evident at any other rpm.

This vibration is also evident while driving in any gear and at any speed that falls within the 1,200 to 1,500 rpm.

I have been chasing this vibration issue since

the truck had 100,000 miles and it now has 190k. I initially believed it was a driveline problem so I replaced EVERY rotating part aft of the transmission, including transfer case, driveshaft, rear differential and bearings and the front wheel bearings—with no improvement for that particular vibration.

I have an evolution programmer on the truck but have disconnected it and the problem still exists. The truck runs and performs fantastic. Can anyone suggest a cure for this engine vibration between 1,200 and 1,500 rpm while truck is in park or neutral? Macon Rounds Via Email We assume the engine is not setting any codes. Otherwise, you might spend some time with a Tech II scan tool, looking at the various engine speed sensors, looking at injector balance, using it to disable one cylinder at a time, or anything else you can think of. Do these tests while running the engine in Park through the engine speed where you notice the worst of the vibration. There's a whole lotta rotating inertia with the engine running at 1,200-1,500 rpm. Something significant is happening if you can feel an objectionable vibration from the driver's seat. It should be measurable using a Tech II. Just a thought—due to how a diesel engine operates (compression ignition), considerable torque impulses can be found in the crankshaft/ drivetrain at certain engine speeds and loads. Generally, the powertrain control systems minimize this to a point of being hard to feel, but they can still be felt. Are you experiencing this while driving with the Tow/haul mode activated and with the engine operating at a lower engine speed? Is there any change in the vibration with/without T/H engaged in the rpm range you mentioned? Keep us posted, and especially the results of the injector balance.