I=92m posting this message in the hope of helping anyone who has problems in getting a DigifantII engine through etest due to high NOx levels.
I have a =9192 Golf 1.8l gas with DigifantII engine control. The car has been in the family since new. In smog tests over the years in both Vancouver, B.C. and in Ontario the NOx emissions have varied by more than a factor of 10, in an apparently random fashion. For example, in one test with just 21,000km on the car the NOx emission was 790 ppm (a fail in Ontario, but a pass in B.C.). At 36,000km without any tuning or other changes the NOx was 36ppm. I suspect the random fluctuation in NOx output results from VW design issues, not a problem with the engine. In fairness to VW, the car was designed to pass the EPA test, not regional smog tests. For example, the EPA test almost certainly allows airflow through the radiator to duplicate that expected in actual driving, while smog tests often allow cars to idle for extended periods, raising the engine temperature above normal operating conditions.
In May 2010 the car failed the Ontario test with the following results:
idle CO 0.06% idle HC 36ppm load CO 0.01% load HC 9ppm load NOx 990ppm
The timing was set precisely as specified in the Bentley manual. A check with an oscilloscope showed the oxygen sensor was operating correctly. The catalytic converter was one year old.
Before retesting the car in November I did the following:
- Fuel with a combination of E10 and E85 to give an ethanol content of about 20%
- Wire the radiator fan to run continuously while the engine is on (done by removing the fan overrun relay and rear wiper relay at the fusebox and shorting between appropriate pins)
- Disconnect the knock sensor, then raise RPM to over 2500 RPM three times. Confirming the comments in Bentley, the timing light shows this reduces the advance by about 10degrees at 2500 RPM
- Disconnect and plug the vacuum line controlling intake air temperature (i.e. only allow cold air to the intake)
- Change from platinum to copper spark plugs
- Raise front tire pressure to 35psi to reduce rolling resistance
The results were:
idle CO 0.08% idle HC 20ppm load CO 0.09% load HC 11 ppm load NOx 373 ppm
Unfortunately this shotgun approach doesn=92t identify which changes were primarily responsible for lowering the NOx. However, all the changes are easy to implement. Of course the modifications should be removed immediately after the test. The car seems to run fine on E20 but it might be risky to use this for extended periods.