I recently bought an 07 f150 Stx 4x4. A few days ago on a longer ride than normal my check engine light came on. I took it to auto zone and the Diagnosis was an exhaust compression problem. It does have an aftermarket exhaust system on the truck. I don't see any performance issues or rough idleimg but it does have the classic f150 mystery whistle under the hood. Does anyone know what could be the problem? I'd like to fix the problem myself soon.

 

What code did you have, and what is exhaust compression? Do you mean back pressure? If back pressure is high, you have an exhaust restriction, most commonly bad catalytic converters. You'd have a p0420 or p0430 if that was the case, or o2 sensor codes.