Wide variation between smog shops

[357]

After swapping back to the stock injectors/AFM and chip on my '88 325is about two months ago, I finally get around to getting the thing smogged yesterday. During that test, is fails due to CO emissions that are over the limit by a factor of 2, and NO emissions that are just barely (5ppm out of 750-ish max) over the limit at both 15 and 25mph. Figuring that the CO emissions are due to a bad O2 sensor, I replace that last night (super easy job, btw) and take the car in for a retest, once again driving around for 20 minutes prior to the test to bring everything up to operating temp. This time, it passes CO emissions with flying colors, but fails massively on 15mph NO emissions (well more than double the limit), and very slightly over the limit on 15mph HC emissions. Figuring that this dude's equipment it malfunctioning, I immediately go to another station and get it tested for a 3rd time, and everything passes with flying colors, despite the operating temp being the same (25 minutes between tests, which was me driving from one to the next).

Does anybody know of a way to report to CARB that one of these guys probably has malfunctioning equipment? Also, does anybody happen to know in which direction smog test equipment usually fails?

[jlevie]

Those results suggest to me that you have bad catalytic converters on the car and that the engine management system is not working as it should be. Marginal or failing cats are very sensitive to operating temperature. They may have been hotter for the last test.