What causes HC(ppm) to be high? (emissions)

[houstonwag89]

Hello all, I've had my '89 Wag for a bit over a month. All of the Emissions controls except the PCV valve had been disabled or removed. With lots of help from this board I was able to get everything put back on. Well this week, I was able to PASS Texas emissions testing!!!! I'm pretty excited about that, but they had to run it twice to get it to pass. The HC was just over on the first run. They warmed it up, and it was able to pass. Here are the results:
High Speed (25mph)
Standard Current Result
HC(ppm) 155 113 PASS
CO(%) 1.91 0.14 PASS
CO2(%) 14.2
o2(%) 0.8
Nox(ppm) 990 490 PASS
DILUTION: >6.0 14.34 PASS

Low Speed (15mph)
Standard Current Result
HC(ppm) 159 144 PASS
CO(%) 1.42 0.26 PASS
CO2(%) 14.2
o2(%) 0.6
Nox(ppm) 1076 670 PASS
DILUTION: >6.0 14.46 PASS

They didn't tell me, but I suspect it was the low speed HC test that originally failed. What would cause that reading to be high? Do any of the other results tell me anything about the health of the engine? I'm very happy that I passed, but just curious what I may need to do to keep it passing in future years. The HC reading is the only one that seems to have a potential problem.

Thanks,
Scott

[babywag]

High HC can be caused by a few things....since it passed my guess would be you didn't get the vehicle warmed up enough?
Before testing I always take mine on the freeway and wind her out a bit.
Should be driven for @ least 20-30 minutes.
A good tune-up may take care of it??

High HC can be;
Misfire(s) Ignition related bad wire/plug/weak spark...
Air/Fuel mixture (carb needs overhaul or re-jet)
Low compression (worn engine)
Bad catalytic conv.

A lot of people speak of adjusting the idle mixture, but that won't do any good past idle.
To change the mixture you would need to install different jets.

[brent]

It's my experience, from setting world records for failing emmisions in an FSJ, that high HC's are the result of something wrong in the ignition system. The state will even tell you that.
I've failed for these reasons, which I've had to fix: improper vaccuum advance; vacuum leak; worthless vapor cannister; running too rich; improperly routed hoses from vac advance.
It'll be something cheap and not obvious in the ignition system. Doesn't hurt to screw down your carb ports (clockwise) before getting in line again.
Brent

[Chevelleguy]

Like you said, they had to warm it up. The cat won't 'light off' until it hits about 500* so if it is not hot enough, it isn't working.

[Spectre]

High HC is running too rich or incomplete combustion.

[drlocke]

Just before going to emissions test do a complete tune-up--including compression check or leakdown test, change the oil, make sure the thermostat isn't causing overcooling, do at least 15 minutes of highway driving before pulling in. Engine must be at full operating temp to be a clean-burning machine.

Idle mixture adjustments are generally not possible for the owner to do in cars built much after 1980.

I solved my issues with the Massachusetts Smog Nazis by going back a few model years on my fleet.

[ October 09, 2005, 08:18 AM: Message edited by: drlocke ]

[2ndtimearround]

Check the power valve on the carb. When mine was leaking, it drove the HC into the stratosphere.