About an hour after I bought my car (89 325ic), I tried to smog it and it failed miserably. I even drove it a while to warm up the car. At 15mph both the HC and NO tests failed BAD. At 25mph, no problem. HC MAX is 108 and it measured 143 NO MAX is 767 and it measured 1520 So a new cat was installed. As well as a thermostat. We decided to do a good old fashioned tune up from changing all belts, plugs, cap, rotor, water pump, etc. I also used some Lucas injection cleaner just for the heck of it. My hubby has Fridays off and took it down to get smogged again yesterday. It barely passed. It's a big improvement from the first tests, but I'm still concerned. Once again at 15mph both HC and NO measured quite high. HC MAX is 108 and it measured 97 NO MAX is 767 and it measured 748 Maybe the oxygen sensor? Any advice would be much appreciated. I'm in CA btw.
You can have the idle/low load mixture adjusted easily. There is a bypass screw on the AFM under a plastic plug. It is designed to adjust idle CO and will have a slight effect on the low load mixture as well. Clockwise is rich and counterclockwise is lean.
Hey Paul, thanks for the info. In CA we're now using dyno's and I believe they're running it around 1800rpm.
I know they are using dynos (how else would they get 15 and 25mph?) At low loads (say running just above idle with no real load on the motor) the flap on airflow meter is barely open, so the small amount of bypass has more effect on the overall mixture than at higher loads. It obviously won't matter for another year or two, but between that and maybe a new O2 sensor, you can probably tune the car for emissions next time with no problems. Just remember that these cars idle much more smoothly if they are a little rich, so if you lean it out for the test, you can richen it back up for smooth idle (because lean misfires at idle are worse for the environment than an ever so slightly rich mix.)
