Cadillac Misfire on Deceleration
Owners of 2004-2011 Cadillac STS, 2004-2015 CTS SRX and 2013-2015 ATS XTS vehicles equipped with a 3.6L engine may comment about an engine misfire and check engine light only on deceleration.
This may be the result of debris in the serpentine belt or balancer pulley, causing a jump and false misfire. Another possible cause is worn engine mounts which may cause a ground-out and false misfire. Note: Do not confuse this with normal roughness and a few random misfire counts that are normal on these engines at the same speeds in park or neutral.
Remove the accessory drive belt and drive or brake-stall at the signature rpm of 1400 to 1800 rpm. If the concern is gone, inspect for debris in the serpentine belt or pulleys that may cause the jump/false misfires. Another inspection: use an engine lift to unload the engine mounts and brake stall at the signature rpm. If the concern is gone, inspect for a ground concern with the mounts.