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I feel I need to relate this story knowing how much time I spent worrying about my 1985 RX-7 GS not passing Houston's emissions test.



I purchased this car on Ebay from a guy in Phoenix, AZ and drove it back to Houston, TX. It had passed emissions in Arizona but I did not witness the test. I had it tested here in Houston with the following results



High RPM (25 mph)

HC(PPM) 824 (197 needed to pass)

CO(%) 2.95 (1.27 needed to pass)



Low RPM (15 mph)

HC(PPM) 959 (203 needed to pass)

CO(%) 2.66 (1.15 needed to pass)



I began to panic because Texas will not allow the car to be registered in the state if it fails emissions testing.



After a visit to the Mazda dealer, he recommended that I have a compression test on the car. It has 127k on this motor so I expected it to not be like a new motor. I also expect to rebuild it sometime in the near future but I wanted to get out a few months before that size of an expense. The compression test results were:



Rotor Face 1 Face 2 Face 3

1, 5.4, 5.3, 5.4

2, 5.5, 5.2, 5.4



According to the Mazda shop manual it should be a minimum of 6. The dealer blamed the engine compression for the poor performance on the emission test and billed me $127.



I was not willing to accept this at face value. The engine runs strong and does not smoke. At this point I went looking on the internet for some advice. I found it on this forum. Someone (sorry about the lack of reference) said that you need three things to pass the emissions test: A working smog pump, a working air control valve, and a working catalytic converter.



I checked the smog pump and it was ok. I started to check the air control valve according to the mazda shop manual procedures. This is where I found a problem. The air from the pump was always going back into the air cleaner no matter what the speed. It should go to the exhaust manifold at low rpms and the catalytic converter at higher rpms. Only if the catalytic converter is overheating or the engine is at very high rpms should the air be going to the air cleaner.



I removed the ACV from the engine and located the air relief valve portion. The vacuum actuated valve would not move no matter how much vacuum was placed on it. Opened it up and found that the diaphram material was hard and stiff (no jokes please) and it cracked when I forced it to move.



I replaced the ACV with a used one ($100) and started the engine. No air was being returned to the air cleaner. After about 10 minutes there was smoke coming from underneath the car. I realized that all the dirt and road oil that had accumulated on the outside of catalytic converter was burning off. Hey! I think that is a good thing.



I took it back to get tested again. Here are the dramatic results:



High RPM (25 mph)

HC(PPM) 77 (197 needed to pass)

CO(%) 0.05 (1.27 needed to pass)



Low RPM (15 mph)

HC(PPM) 79 (203 needed to pass)

CO(%) 0.07 (1.15 needed to pass)



Wow! A 90%+ decrease in hydrocarbons and the CO was down to nearly nothing! Hell, this is the cleanest running car that I own!



So if you find yourself in a similiar position, don't panic! Buy or download the mazda shop manual and check the air control valve!



Thanks for all the help!



TheTeep

Thats great news, we don't have smog checks over here in Australia, but keeping the air clean by passing emmissions test properly than using "pass with this **** in a bottle" anywhere, is important.



That was Mike that told you the three things needed to pass.

He's the man.

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