I have a 1998 EB with 275,000 miles. One morning I went to start it and it wouldn't, ended up cutting the cat. converters off and it cranked right up. But has an awful backfire/popping noise in the engine. It wont stay cranked now unless I rev the engine. As far as I can tell other than the popping backfire thing the engine is blowing air instead of sucking air. Any suggestions?