I need help cleaning up the emissions on my ZC motor (standard ZC 1989 vintage). I went to have my yearly state emission test with the new ZC motor and it failed on the Hydrocarbons. The readings for the 2500 RPM test were 67 ppm (220 allowable) and 363 ppm at idle (220 allowable). The NOx was pretty high also but they weren't required to test that part. When I put the engine in a few months ago I did all the normal replacement of tune up parts - Spark plugs, spark plug wires, distributor cap & rotor, and ran a bottle of SI1 fuel injection cleaner through it. The guy at the testing center was kind enough to test it in manual mode to see what kind of HC it was putting out at different RPMs. When he let off the gas the HC count went way up to 1000. He said it was probably the Catalytic converter and although I somewhat agree with him on that, it doesn't explain how the HC count was so low in the previous years tests. Last year it was 78 at idle and the year before it was 68. I think the cat is the original with 200K miles on it, but if it was in about the same shape the year before why did it run so clean? I have also checked the timing and both cams are aligned where they should be in relation to the crank. I was thinking of getting an AEM adjustable cam gear and taking it to the dyno and see if I can dial out some of the HC. Is it possible there is too much overlap in the exhaust cam? I also have 3 different computers I can try in the car, an SI, a 88 Integra, and the ZC one which is the one I have been running. I think by just sticking on the cat it will probably clean it up enough, but should the motor really run that rich?
Ryan Cumming, GA
