I just bought a 2010 Ford F-150 FX4 with the 5.4 V8 and 206,000 miles. The cat and one o2 sensor (bank 1 downstream sensor) were stolen so I replaced the sensor and installed an exhaust assembly with the cat already fitted though it doesn't fit exactly so part of the pipe behind the cat is still open to the air. It still has the issues it first had. It will start normally for a second then the rpms will drop below idle and may cause the truck to stall (not always) and then they will raise to idle. I can feel a bit of a rumble at idle. If revved in park, it will got to about 2000 rpms then not want to rev any further. It also doesn't like the throttle being pushed down to hard while driving. I checked the codes and these are what they are. Transmission feels excellent and the engine doesn't make any noises. Would a blown fuse cause any of the issues? Any help will be greatly appreciated.
problems can just be caused by a leak after the cat before the muffler?
maybe.
Reduced exhaust velocity = less cylinder scavenging
If it doesn't fit exactly, as you stated, you have the wrong parts that won't ever work correctly.
It was made to fit and it connects to the pipe to the muffler and the bank 1 manifold just fine but the exhaust near the bank 2 cat had been modified so it will have to be remodified to fit the cat. Would have fit just fine if the short pipe behind the cat to the rest of the exhaust wasn't messed with.
Get it back to stock, all of it and it'll probably work just fine. Why was the exhaust near the Bank 2 CAT modified? How badly was it modified?
Not sure. It looked an extra piece of metal was added on to the existing exhaust past the cat. All of these problems can just be caused by a leak after the cat before the muffler?