OK, after installing a new magnaflow cat from y-pipes back to muffler, I have developed a rattle or knock from either the air pump pulley or alternator pulley. 1995 F-150 5.0 V8, 132k. The only thing thats different was I tied off the excess exhaust hose that originally fed into the exhaust pipe between the resonator and catalytic converter. On the new one, there is no feed-in and a buddy told me to just block it off, that the excess exhaust from behind the headers would come out the regular way. Any ideas??

 

Probably the air pump.
Its pumping against itself.
Try to eliminate by removing belt(s) to isolate which pulley.

 

Hey 88racing, thanks for the reply. Does the air pump pumping against itself like you said have anything to do with blocking off that exhaust hose, and what damage am I doing to the air pump in the meantime? And by the way, I have the serpentine.

 

There are several ways to go about solving your problem.
1. Find an exhaust shop to weld in a new bung and tie the line back in.
2. If it's possible find a new serpentine belt to bypass the pump. It's going to be shorter. But you may get interfearence from the air pump pulley.
To find out what size shorter belt you are going to need, take the original belt off(remember how its routed).
To measure for a new belt»
Take a flexible cloth tape measure or a string and follow the path of the original belt around the pullies, don't go around the air pump pulley. Remember to add 1/2"-3/4" for deflection of the belt tensioner.
You may have to buy 2 or three belts to get the correct size.
Edit: If you live where there is emission testing. Make sure the bypassing of the air pump doesn't conflict with local/state emission laws.

 

Ok, one more question. What if I just leave that exhaust hose hanging, so to speak. I read a post about air pump delete from a few years ago about totally bypassing the air pump, but that it helps warm up the cat, and sends air to the exhaust and all, but what if I just openned that hose back up? Thanks again!!

 

You could do that also.

 

Hey 88. Luckily I kept the metal downtube that connected to the rubber hose that came out of the back of the engine, and was able to squeaze my arms past the exhaust and reattach the two back together. No more air pump pulley rattle!! Thanks for your input. Now, can Junior turn things around this year?!?!