Hi, this is my first post. And if the english is bad, well... it´s because I´m from Sweden.

I´ve got problems with the CO and HC emissions. The car failed the test here in Sweden. It´s a 1989 Pontiac Trans Am GTA with the 350 TPI engine.

The results from the swedish test:
CO 1,0 (max.allowed 0,5)
CO 2500 RPM 1,2 (0,3)
OXYGEN 0,97 (0,96 - 1,25)
HC 137 (100)

I only passed the oxygen test.

- The SES-lamp does not flash any codes.
- I´ve recently changed the spark plugs, oil, oil- and air filter.
- Both the CO and HC went down when the crankcase ventilation was opened so the engine got more air. But the oxygen emission went up.

Fuel consumption: 1,5-1,8 liter / 10 kilometers.

I hope this information can give you any idea of what the problem is.

 

there are a few integral parts in your emissions system that you need to go through

-Pvc valve -- on the driver valve cover
-egr valve -- on the manifold -- toughest to get to but is very doable
-catalitic converter -- welded to the exhaust
-air injection into your exhaust manifold -- is driven by the serpentine belt--the pump drives air into your exhaust manifolds to help heat them up to burn emissions faster
-charcole canister -- in the front of the engine bay where your air intake is located towards the left front.

typicaly speaking its the cat that goes out first ... if you havent replaced it in quite some time then its due (2 years). The Egr valve is also crutial in its role in passing the emissions test. It can be tested but needs removal from the manifold first. If I where you I would check to see when they put a cat in and try to replace it. But do make sure that the other parts are in working order so that your not just throwing money at it.
good luck

 

the converter is brand new. So it should be working.

Even if I´ve got headers on the car, I should still pass the emissions test? The AIR system is not hooked up because it can´t be installed in the headers.

 

Yes. I passed with headers, a fairly new cat conv (used once every 2 years), no air pump, and no EGR. The LT4 HOT cam in my engine has enough overlap for "self-EGR" at lower engine speeds.

 

If you suspect your english is not good, you should try MY swedish...

The exhaust gas is too rich. Did you have a test result for oxides of nitrogen (NOx)? If that was acceptable, the EGR is not an issue, and you may want to increse the combustion temperature. Leaning the mixture may also help if it doesn't increase NOx beyond the limits. More timing advance may also help. Also, can you get ethanol blended fuel? That will make the exhaust very lean and keep the NOx levels low. It may be worth running a tank of it for the test.

Adding A.I.R. to the exhaust would help when cold, but if the cat converter is a 3-way without an aspirator tube, A.I.R. won't help for the test. If the cat has an air tube, it should be connected to a working pump, or at least a passive pulsed injection system of check valves.

 

The 350 should have air going to the CAT for downstream closed loop operation when warm. The air to the manifolds are for cold open loop operation and shouldn't affect closed loop (except if missing items are needed to pass). It looks to be a 2 speed Idle Test not a dyno test. EGR only works when trans is in D. I'm sure if NOX was a factor you would have listed that. If the emissions drop when the PCV is out, you may have contaminated oil, change it. Installing the air pipe to the CAT would be a good idea to help with the CAT to reduce the emissions and probably your best bet. The numbers you list are excellent readings for a car without a CAT. Maybe also a defective CAT. If you could list all 4 gases at idle and 2500, a lambda calculation could be used to see if you are in fuel control. If in fuel control, the CAT would be the obvious culprit.

 

The mechanic that´s working on my car can´t find anything wrong with the engine. He suspects, like you are thinking, that it might be the CAT.

It´s a brand new CAT, installed 3 weeks ago. Just my luck to get one that´s not working properly....

 

also dont forget to warm up the car as this would give the catalyst time to heat up to burn more emission off ... and as vader recomended leaning out your mixture is another way to help you push passed the sniffer test
well hope it works out

 

welcome to the thirdgen boards. your english is pretty good for someone from Sweden, its better than some who live here

some other things else to check,
make sure the motor is getting to full operating temp, if you have a colder T-stat than factory that will hurt emissions. are the cooling fans wired so they run all the time? if so that can cause the motor to run cooler than what it should. if the motor is getting hot enough, check the coolant temp with a scanner.
check the O2 sensor with a scanner, if its more than about 2 years old it won't hurt to replace it, they do get tried with age.

 

The only problem with warming up the car, is unless it's probed right after the warm up (driving the car will get the engine hotter than just running it at 2500RPMs), you will lose any heat build up in the CAT by idling the engine or running at 2500 in park. Leaning the mixture could cause the HC's to increase. As DENN_SHAW said, a colder stat could cause a richer mixture and fail. Engine temp at test should be at least 200 degrees F (aprox 100 degrees C).