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This Preliminary Information communication provides information to the technician the steps needed to diagnose and repair vehicles with a rough idle and/or vibration at idle in Drive. This condition will not be present in Park, or Neutral. This concern may be caused by ground out within the one or both engine mounts. Technician will use CH-51450-A (Pico Oscilloscope) to measure the vibration disturbance. If the vibration concern is E1.5 in the horizontal / lateral direction with Pico sensor mounted in seat track as indicated ? continue with steps to reduce the amplitude of the vibration by adding spacers in key locations to reduce ground out within the engine mounts. The 6.2L engine has a characteristic E1 which can be felt, and may be described as a lopey idle. Do not confuse 6.2L E1 characteristic (not caused by mount ground-out), with E1.5 normal idle characteristics being transmitted into the truck via ground-out thru the engine mounts. If measuring high at the seat track 12 mg or greater; replacement of the engine mounts should help reduce the amplitude of the vibration. If the disturbance measures at the seat track as E 1.5 lateral in the range of approximately 2.5 - 8 mg using a tri-axis sensor. Then place tri-axis Pico sensor on the inboard seat track forward-most location to record measurement of the rough idle vibration concern. With the Heater-Vent-Air Conditioning on perform several short heavy launch events from stop to stop to bring the temperatures back up while attempting to re-create the rough idle vibration in Drive with Pico sensor placed on inboard seat track; while the vibration is active ? Record Pico reading. This method seems to provide better results than extended test drives. If the Pico reading for E1.5, with vibration active, at specified seat track location measures close to 2mg or less use Service Information to diagnose rough idle / vibration. If the Pico reading for E1.5, with vibration active, at the inboard forward seat track

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Date Published
DEC 19, 2014
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