Smog

[Tim Rogers]

Dan wrote:

"I have no mods of any kind but it failed last time due to high HC's. My
timing is
at 17 degrees. Will rolling it back to 15 or maybe even 13 degrees help?"

Timing should have little effect on your HC's.
High HC's are caused by having:
A) A mixture that is too rich,
B) Incomplete combustion, or
C) Ineffective emission control devices.

Situation A can be caused by:  leaky or clogged injectors, clogged fuel
filter, bad fuel pressure regulator; misadjusted or bad throttle position
sensor (TPS), MAF or O2 sensor.
Situation B can be caused by faulty ignition items: Plugs, wires,
distributor cap or rotor, coil, etc.
Situation C is generally a bad catalytic converter or PAIR/AIV, but most of
the electronics in the injection system can also be considered emissions
control devices.

So, the first thing to do would be a tune-up, replacing anything that is old
or does not test out to FSM specs.
Checking your O2 sensor is a must in this situation.
If everything else checks out, this would point to a bad CAT, but make sure
_everything else_ has been checked out first.
If your engine has been running rich for a while, this could increase the
chances that your EGR/BPT has gotten carbon fouled, but if you just tested
fine for NOx, then that system should be fine.  The EGR/BPT system has no
effect on HC emissions.

Tim Rogers
-93 NX T-top -needs motor work
-91 NX - Racecar-to-be
-75 Silverado - Rusty Beast
-01 Astro - Work Van, Tow Beast