You where writing to Sean Dunbar;
>  SD> Depends on the car.  In some, there's a tube going from the pump
> into
>  SD> the  exhaust manifold(s), and it forces a little air in there to
> help
>  SD> reduce  hydrocarbons.  On others, there's a tube going from the
> pump
>  SD> into the  catalytic convertor (most notably Fords.. I know the
> Ranger
>  SD> mini-trucks were  ilke this in the early 80's, don't know about
> now)...
>  SD> on mine, it's hooked up  to a tube going into the top of the
> engine,
>  SD> and I assume it ends around the  exhaust manifolds.
> 
>         In either case, it serves the same purpose.. the get the Cat-con
> 
>         to work better. Now then.. if I could just remember what the 
Not in all cases. Pre-1975 (pre-cat converter years) an air pump obviously
has nothing to do with helping heat up the cat. conv.  Its primary purpose
is to burn up any remaining fuel in the exhaust and thereby reduce NOx
emmisions.
More ubi; late 70's mopars "air injection" went into the back of the heads.
>         frag we're talking about this for.. ??  Backfire? Was that 
>         it? Something about removing the Cat to cure a backfire? May do 
If its got an airpump and its backfiring (when decelerating), one of the
check valves may be faulty, or one of the tubes may have a loose fitting
past the check valve, or cracked air tube pipe (past the check valve).
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