Engine Intermittently Rattles or Runs Rough with MIL Blinking?
While driving under steady cruise (between 30 and 65 mph) or light acceleration, does the engine intermittently rattle or runs rough with the MIL blinking? Since these driving conditions are likely to activate VCM operation, the probable reason for these symptoms is sticking VCM rocker arms. Here the lowdown.
- Engine Rattles Going into VCM: This noise can be quite noticeable. What you’re hearing is the VCM rocker arm pin tapping against the other rocker arm as it tries to lock the two arms together going into valve pause.
- Engine Runs Rough with MIL Blinking: The VCM rocker arm pin can also stick in its locked position, causing both rocker arms to stay connected. When this happens, the engine intermittently runs rough and the MIL blinks.
If the engine is shut off and then restarted when either of these symptoms happens, the rocker arms may unstick, allowing normal operation with no misfire DTCs being set, which can make this problem tough to troubleshoot. To help you out, be sure to check out the Variable Cylinder Management Rocker Arm Test in SIS. It can help to determine if the rocker arms are working right.
So, if you get a vehicle in your shop with either of these symptoms and your client reports it intermittently happens under steady cruise or light acceleration, it’s most likely from sticking VCM rocker arms. Replacing the affected rocker arm(s) usually fixes the problem.