I have a 99 half ton Chevy pickup. Not Silverado. I had a cat delete exhaust put on and I only get about 8 MPG.
HUMMMM.BELIEVE IT OR NOT YOU NEED BACK PRESSURE EVEN RACE CARS ARE USING THEM NOW...OK..YOU DID NOT SAY WHAT SIZE PIPES WERE STOCK..WHAT SIZE DID YOU PUT BACK INTO IT??/ 1 OR 2 CATS/MUFFLERS..THE NEW BRAND NAME OF THE MUFFLERS...IMPORTANT ALSO MOVING ON DID/HAS THE AIR INTAKE BEEN UPGRADED TO MATCH THE SUSPOSED EXTRA EXHAUST FLOW???? AN EXHAUST CROSS OVER??1 OR 2 TAIL PIPES/EXTENSIONS????
Has nothing to do with backpressure.......you removed the O2 sensors didn't you?
upstream O2 sensors remain downstream were tuned out in the computer
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