[1224bret]

Check to see which cylinders are misfiring if your sure its not fuel related then check plugs or replace if needed if you still have the issue then if it's only one cylinder it's probably a coil if its one full bank it's probably the switch box for that bank (the two boxes mounted on the right side of the engine one on top of the other) one switch box controls one bank the other controls the opposite bank. If its two cylinders on separate banks then its probably the trigger or trigger wiring. (The trigger is mounted under the flywheel) I've seen a lot of older mercs with broken wiring right at the trigger. The trigger moves and advances the timing when you move the throttle over time with it moving back and forth the wires break. You can repair them sometimes if the aren't broken to high up but it's a temporary fix. If it were no fire on all cylinders it would be a stator issue but that's obviously not your problem.