.... It had an early and feeble
attempt at emission control but I left it all off when I changed a
head gasket and the truck was much more efficient without it.

Doubt it very seriously... you probably had a clogged line
or vacuum leak long before you took it all off. Those
systems were actually quite good when working properly. They
were a bit on the fragile side though.



Frank Boettcher wrote:
I don't know. It had the pre catcon system that injected air into the
exhaust manifold just south of the exhaust valves, looking for a post
cylinder burn. Had a air pump that was belted off the crank pulley.


This was a '78? Our shop truck was a few years newer but I
figured the system would be somewhat the same.

That system seemed to rely partially on a retardation or dwell of the
throttle dump. When you took your foot off the pedal it would not
immediately drop but slowly come down.

That doesn't sound good. In fact, if it was doing this from
day one, I wonder if yours was not put together right.
Certainly post-combustion air injection shouldn't have this
effect.

.... Made it a little tricky to
shift a manual.

I bet so!

... Additionally, it had a tendency to backfire
excessively on deceleration. All of this from day one. Others
complained of burned exhaust valves


Sounds like a bad system, either some engineering oversight
or poor QA.


When I took it off (or more accurately didn't put it back on when I
chaged the head gasket and did a valve job), it ran so much smoother.
Immediate throttle dump, no more backfiring and no hesitation. Gas
mileage increased by about 5 percent. So it ran more efficiently as I
stated, but I can't comment on the relative emission effectivity.

They didn't use that system for very long.


Obviously I can't claim to be an expert on all
pre-electronic emission control systems, but as a combustion
control technician I've seen all sorts of hacked-up BS
excuses for post-consumer systems... none of them have ever
worked for s&*#. The real problem most of the time is poor
maintenance, for example the vacuum regulated systems on
many cars (late 1970s thur the 1980s) worked quite well...
*if* the hoses weren't crimped or some part of it
disconnected or leaky. Then of course, the people who worked
on them "informally" were usually not sophisticated
mechanics anyway, and tended to regard all this new-fangled
complex stuff as junk... indirectly sabotaging the system
and thus justifying their prejudices... kind of like the way
some sailors are...

Nowadays, CO and O2 sensors are a lot better than they used
to be, combustion control can be very precise & reliable
which improves fuel economy and engine longevity. Big
plusses! I still dislike all that electronic crap hooked up
to my engine though

Regards
Doug King