Yeah the 281 means your #7 cylinder is contributing as much as the others.The 1668 is most likely caused by the 281 code unless you have a chip.This could be becuase of the harness under the valve cover is coming unplugged and or burnt,could be the injector itself and god forbid could be a base engine concern.how many miles on the rig?The first thing to do is remove the drivers valve cover and check out the harness,ohm check it, if it's ok you should do a compression test then if that checks out replace the injector.
