1993 mazda b2600I engine knocking

A couple of things (besides a plain ol' wore out motor): Plugged exhaust/cat: carbon build up on the piston(s): Jumped timing: bad fuel: mis-routed plug wires

If it idles good, OK, But on acceleration pressure it fails. But it sounds like it needs air, intake to me Just my guess

Sounds more like a plugged cat.

hmmm. that could me, The car has a new exhaust from the cat back

A plugged catalytic Converter will cause a backfire condition - lean - no air out - no air in. You could hook up a vacuum gauge and watch how it acts as you increase RPM to say 2500 and hold it there for several seconds - is the reading low or does it fall off at a steady speed? You could disconnect the exhaust at the manifolds and run the engine - noisy but effective. A muffler shop has the proper tools to make a hole in the pipe and measure the back pressure.

would it matter that i dont have any backfiring?

No.

Hey guys.. I'm wondering if the front end of a 92 b2600 is interchangeable with the 99 model (guards,bonnet etc)