I recently found a cure for sticking pawls. Go to a hardware store and get that tool that magnetizes/demagnatizes screw drivers. Remove the pawl and pass it over the top of the tool. This works for sticking DC horn relays too. Some guys have said in the past that you can remove the magnatizm from E unit pawls by striking them with a hammer. I do not advise that trick. Make sure of course, that the E unit and pawl are clean and oil free. Re-wire BOTH of the wires to the tender. Sometimes dirty track will cause it to not work. Did you clean the contact points of the whistle relay? If you are using an old, unmodified Lionel transformer that may cause your problem as well.
Rob
