Car is an 89' 745 Turbo with a 93 motor with about 88K miles. In 2004 my passing numbers after replacing the original cat were: at 15MPH, HC: Meas 81 Max 112, CO: Meas .20 Max .72, NOX: meas 756 Max 778, and 25MPH, HC: Meas 47 Max 86, CO: .05 Meas .6 Max, NOX 81 Meas 717 Max. Fast forward to 2006, and 30K miles more. Prior to 1st test AMM was adjusted, O2 sensor checked, oil, plugs (NGK Iridium)and filter changed. I knew the that a part of the substrate in the cat had broken off, but I figured I would test anyway, since where I took the car you get a free retest if you fail the 1st time. So the numbers at 15MPH were HC: Meas 103 Max 116, CO: Meas .80 Max .74, NOX: Meas 2450 Max 791, and 25MPH, HC: Meas 102 Max 91, CO: .76 Meas .62 Max, NOX 2573 Meas 730 Max.
Big time gross polluter failure. The only passing number was HC at 15MPH. Before I retested, the ignition power amplifier died in traffic, so I had the car towed to my mechanic and had it replaced. With the new one the car ran better than it had before, and I thought it ran great then. Idled smoother than ever.
Before retest last Friday afternoon I bought a Carsound bolt-in cat for $104, and when I removed the old one I saw that subtrate was completely gone. I also retarded the timing to 10 degrees, and added a bottle of Techron to 3/4 full tank. Retest numbers were at 15MPH were HC: Meas 15 Max 116, CO: Meas .03 Max .74, NOX: Meas 10 Max 791, and 25MPH, HC: Meas 10 Max 91, CO: .04 Meas .62 Max, NOX 14 Meas 730 Max.
I was totally amazed with the numbers. The percentage of reduction in the measured numbers at 25MPH were HC 99.9%, CO 99.48%, and NOX 99.99% !. In 2004, with a new cat I barely passed NOX at 15MPH. So I think that the new cat in 2006 is partially responsible for the huge improvement. The rest is due to the other changes. It would be interesting to test after each of the 4 changes to see the difference each one made. I especially wonder about the power module.