Tuning to low emissions: a study of the effect of service and maintenance on emissions from in-use vehicles

To demonstrate the importance of periodic tune-up, the effect of service and maintenance on exhaust emissions of in-use passenger cars was studied with 19 vehicles of various age between model years 1982-1989. Apart from the 16 non-catalyst cars, the batch comprised 3 catalyst equipped vehicles. Of these, one was retrofitted with an open-loop system, and the two others were closed-loop TWC systems. Among all the cars, the odometer reading ranged from 15000 to 226000 km. The service and tune up was found to reduce CO emissions by some 25%. Even HC output was lowered, but to a lesser extent (about 5%). On the other hand, the emissions of nitrogen oxides (NO_x) were somewhat increased (13%). These effects were most accentuated in the case of the non-catalyst and carburetted vehicles, and somewhat less in cars with fuel injection. The catalyst-equipped vehicles were least affected.