Specifically what are the OBD-II codes the car is generating? "Tune up" and "vacuum leak" are WAY too generic for diagnostic purposes. Also, the hole in the exhaust before the O2 sensor is a bad thing. The O2 sensor will now sense a lean condition and will compensate by reducing the amount of fuel the engine gets. This could also conceivably create the "vacuum leak" you say the computer is showing--a lean condition. Backpressure is NOT a concern with modern cars unless the catalyst has melted and is blocking the exhaust system. The catalyst should never fail for the life of the car. If it does, you've got more problems to deal with than just a melted catalyst. Jeff Reeves Auburn, GA 01 Grand Cherokee Laredo 72 Javelin SST 68 AMX (x2) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://list.amc-list.com/pipermail/amc-list-amc-list.com/attachments/20100824/2c42fe2d/attachment.htm> _______________________________________________ AMC-list mailing list AMC-list@xxxxxxxxxxxx http://list.amc-list.com/listinfo.cgi/amc-list-amc-list.com