What type of test and what are the most recent numbers? What, if any, "conditioning" was applied prior to running the test?

The California Bureau of Automotive Repair, the state agency that oversees emission testing, has tagged the M103 as a "high emitter profile", and indeed, most of the test results I've seen on these engines show high HC on the first ASM test, which is run at 15 MPH under relatively high load. The second test, 25 MPH at relatively lower load usually shows signficantly lower HC and lower O2 content, indicating greater oxidation efficiency in catalyst.

My theory is that the catalyst bed cools down and I have used an IR gun to measure the surface temperature of the catalyst inlet after five to ten minutes of idling, and it drops to as little as 300F.

I maintain my car rigorously - duty cycle is right on the money, O2 sensor output is nominal, new plugs, cap and rotor, and I'm still at the ragged edge if I don't take specific action to ensure that the converter is hot, such as holding higher than idle revs prior to the test or going on a rainy day and asking them to run the "tire dry test".

It just seems to be the nature of the M103 beast that the emissions are high unless specific steps are taken to keep the catalyst as hot as possible. It's too bad the initial timing cannot be adjusted on these engines as retarding it five or so degrees from the set nine degrees would probably increase the EGT enough to keep the converter sufficienctly hot to oxidize efficiently for the entire duration of the test, which would yield a lower HC reading at 15 MPH rather than being on the ragged edge or marginally failing.


Duke