[Hib Halverson]

California wants to force old cars off the road. It does that by changing the maximum limits for pollutants. It's been done three times since my 95 has been in the smog check starting in 2000. One of the cars this reduction sometimes impacts is the ZR-1 and it's usually oxides of nitrogen where the engine has trouble passing.

My car is registered in an enhanced smog check area of the State so I have to test on the chassis dyno at 15 and 25 mph. When I want to test in 2006, the car flunked NOx at 15 mph. Initially I couldn't understand why that happened because it had easily passed before and the engine was in good condition.

Later I learned the State was fooling with the max limits in order to flunk some cars which were marginal in their compliance even when they were in good condition and running well. In some cases were the owner cannot get a low-income exemption, the choices are scrap the vehicle or sell it out of state...exactly what California wants.

I spent a couple of days road testing the car and taking engine controls scan data and learned that the stock 93-95 calibration turns the digital EGR valve on at 17 mph. Getting my car to pass NOx at 15 mph was a simple as having an aftermarket calibration engineerwho knows how to change the closed loop parts of the cal change the EGR on from 17 to 14 mph. After that the car passed easily. Unfortunately, while this might be a solution for a 93-95 with EGR, it won't help a 90-92 which does't have EGR.

To correct some misconceptions about the Smog Check.

The standards are the same all over the state. They do not vary by geographical area. That said, the test, itself varies. The standard smog check is done with the car in neutral and the engine at idle and fast idle. The enhanced smog check is done on a chassis dyno at 15 and 25 mph. Enhanced areas are generally the urban ares of the state and a few rural areas with air quality problems.

Lastly, there was a post earlier in this thread about CAGS being for fuel mileage. It is true that CAGS offers an improvement in fuel economy, but that's not why the system was developed.

CAGS (for Computer-Aded Gear Selection) was developed as a way to get the ZR-1 through the Federal pass-by noise test. The test required the car to start in first gear, then shift to second and pass by the microphones at wide-open throttle. The way the test was structured had the car at an RPM which it made a lot of noise and to quiet it enough would have required a lot more exhaust restriction. A development engineer had an idea to use a computer controlled "gate" inside the transmission to lock out second gear and force a shift to fourth, ie: this made fourth temporarily second gear. Obviously this had the car going by the mics at a much lower rpm and making much less noise. CAGS enabled the ZR-1 to pass the pass-by noise test without a much more restrictive exhaust.