My 1986 740LGE non-turbo wagon just failed the California smog check as a gross polluter (for high CO). Stupid me for not knowing that I should have asked for a pre-test, and the smog station cannot suggest one by law. The car has around 380K (on the original engine as far as I know, I've owned it from around 100K). Without paying for a diagnostic, the consensus between the smog shop and myself was that the converter was the most likely suspect and I took the car to another shop where a friend arranged to have a new converter installed. After taking it back to the smog shop, it still did not pass...even after I took it out and drove it on the freeway for 45 minutes. It was very close, though, 121 on the HC where 120 is passing and 1.10 on the CO where 1.00 is passing (the smog tech said CO dropped to as low as .90 during the 30 second test, but the test takes the highest reading). So the car is right on the borderline of passing. I drove it as a freeway commute vehicle for years, but in the last year it has mostly been driven around town. Spark plugs, cap & rotor were replaced a few thousand miles ago. The smog shop thinks that maybe driving the car as much as possible at freeway speed will "condition" the cat and perhaps permit the car to pass smog. I'm also going to change the oil right before I take it back later in the week, and make sure the car is driven at least 45 minutes before the test. Does anyone have any other ideas that might help me keep my poor old car registered and on the road? Thanks!


Originally as tested ~ After new cat ~ After new cat & 45 min drive

RPM: 941
%CO2: 12.1 ~ 13.7 ~ 14.0
%O2: 1.6 ~ 0.7 ~ 0.5
HC (Max 120, GP 270): 180 ~ 156 ~ 121
CO: (Max 1.00, GP 2.50): 3.02 ~ 1.17 ~ 1.10