qsd-dan . . .
You’re right that older can sometimes be better, but not always for the reasons you think. I’ve known a variety of older cars here in CA that pass smog testing with little or no trouble, and some others that are a big pain in the tail even if perfectly maintained. ‘80s stuff IMO is often the best, in that it was new enough to have fairly decent fuel injection, but old enough to have some real adjustment capability. I had a couple of Fiat/Bertone X1/9s that gave very little trouble with their simple but intrinsically clean 1.5 liter single overhead cam engines and Bosch L-Jetronic injection. By contrast, my ’87 Saab 900 Turbo had a known history, ran like a clock and used no oil, but was difficult to smog in spite of having a much more advanced twin cam, four valve per cylinder engine and supposedly superior Bosch LH-Jetronic injection. The difference in injection was the secret: L-Jetronic uses a crude flapper valve potentiometer to measure airflow, and an equally crude adjustable bypass to alter the air-fuel ratio at idle. LH-Jetronic uses a fully electronic hotwire airflow meter with a tiny electronic “pot” to allow for adjustment. This is mostly useless and can’t compensate for old electronics that don’t quite meet their design parameters anymore. On the Saab (and Volvos too, according to my smog man), this results in lean running and ever so slightly high Nox. The fix? A brand new several hundred dollar airflow meter. Meanwhile on the Fiat one just put a voltmeter on the lambda probe, and adjusted that fat bypass screw until it fluctuated correctly. Like the smog tech on your Toyota, I had at least one man look at the old Fiat and ask what on earth I'd done to make it so clean!
A ’92 Eagle my family had from new and maintained very, very well was virtually impossible to smog once it was eight years and 75,000 miles old – Chrysler’s engine management systems by then had no adjustment for either mixture or timing, and no distributor either. I managed to build a trick EGR valve that would barely enable the car to run, but would pass smog. Like the Saab, it wasn’t very dirty, just on the edge. No doubt a replacement of every sensor on the engine and the ECU would have fixed it, but only at a cost of thousands of dollars, assuming that Chrysler would even have had the parts (not likely in my experience). Until I went through this, I thought stuff like fully electronic airflow meters and distributorless ignition systems was fabulous, now I know better.
