I am wondering if; 1.) anyone has experience w/catalytic converter failure and its potential effect if any on the fuel economy gauge reading. My 200k+ '87 245 is failing to get its usual 24/25 mpg and the fuel economy gauge is reading closer to the red than usual. I have also noticed increased exhaust noise and a clunking/rattling sound coming from the catalytic converter (likely the original) which seems to have failed w/o clogging, it sounds like the catalytic matrix/media is tumbling around in a lump. I've ordered a replacement unit but I'm wondering if the replacement is likely to increase or decrease mpg's? 2.) Is low manifold vacuum indicative of good fuel economy & high manifold vacuum bad? 3.) What if any relationship is there between oil pressure and manifold vacuum?
Thanks for any comments or explanations.
Mike