Drive Clean, old A2s, and NOx emissions

Recently there have been quite a few postings to this group regarding older A2s having problems with Ontario's Drive Clean emission testing program. I thought my experiences with passing this test might be of interest to others.

I have a '92 Golf with the basic 1.8L 8 valve gas engine and manual transmission. The car has an unusual history- it was purchased new in Vancouver, B.C., and for the first eight years of its life was only driven a few thousand kilometers each year. The car was emission tested every year under B.C.'s "Aircare" program. The tests were always done in the same centralized, government-operated facility. The results for the

40kph test under load are listed below.

Year: km: HC: CO: NOx:

1993 2,000 19ppm 0.01% 12ppm 1994 6,000 12 0.00 4 1995 12,000 1 0.01 378 1996 21,000 0 0.00 798 1997 26,000 4 0.00 791 1998 31,000 3 0.00 490 2000 36,000 2 0.00 26

All these results were passes in B.C. The main point is that the NOx emissions for this car are all over the map. It's worth noting that the results in '96 and '97 would have been fails in Ontario, but the 2000 result is very low. I have discussed these results with the head mechanic at a local Volkswagen dealership, and he could not explain the almost random variation in test results. I have a suspicion that the time spent idling before the test (sometimes as much as half an hour) strongly influences the results. It's possible that the engine becomes overheated during idling, increasing NOx emissions, or perhaps the 3-way catalytic convertor doesn't remain hot enough. Unfortunately I did not keep accurate notes on the time I had to wait before each of these tests, so I can't confirm this theory. I'd be interested in similar experiences recorded by A2 owners in B.C. and elsewhere. Collectively we may be able to figure out exactly how these cars should be prepared to pass emission tests.

To complete my story, in 2001 I brought the car to Ontario. The car passed its first Drive Clean test. I've lost the results, but I recall the NOx was close to the limit. In September 2004 the car (now at

94,000 km) failed a Drive Clean test, posting the following results for the ASM 2525 load test:

Year: km: HC: CO: NOx:

1994 94,000 0ppm 0.01% 764ppm

Following suggestions from this Newsgroup, I checked the timing and oxygen sensor operation. The timing is retarded by 2 degrees, which shouldn't pose a problem for NOx emissions (advanced timing increases NOx). The oxygen sensor output cycles between 180 mV and 800 mV with sharp rising and falling edges and a period of about 0.5 seconds at

2,000RPM, indicating that the sensor is in good condition and the mixture is being held close to the desired stoichiometric value. The system responded immediately to an artificial intake manifold leak created by removing a vacuum hose, adjusting the fuel injector output to maintain stoichiometry. The manifold vacuum is 15" at idle, rising to 23" at 2000 RPM. The vacuum responds immediately to throttle snap tests, indicating no blockage in the catalytic convertor. Like most A2s this car has no EGR system.

To prepare for a retest, I switched from ethanol-blend gasoline to non-ethanol premium, since there is some evidence that ethanol blends increase NOx emissions. I ran a tank of gas mixed with commercial fuel injector cleaner, then refilled the tank. I replaced the coolant with pure water (and Redline Waterwetter) to lower the head temperature. I modified the aircleaner to take in only cold air. I raised the pressure in the front tires to the maximum allowed value to reduce rolling resistance. I ran the car for half an hour at over 100km/hour immediately before the test, then kept the engine running at 2,000RPM while I waited for the car to be tested, to try and keep the catalytic convertor hot. After all this, the results were:

Year: km: HC: CO: NOx:

1994 95,000 4ppm 0.00% 628ppm

The NOx emissions were still high, but just under the 633ppm allowed limit in Ontario.

I closing, I'd like to thank everyone who replied to my original posting with suggestions on how to lower NOx emissions.

Garry Ottawa, Ontario

snip

Well congrats for passing the test and I will assume you meant to say the year as being 2004. ;-) Or you have a darn good memory.

I thought that NOx would be affected by heat by the engine or even the cat. conv.. A rich mixture overworking a cat. conv. could make the exhaust super hot coming out of the tailpipe. Retarding the distributor would cause the engine to run hotter but should reduce HC. Does your knock sensor work? If not the engine is not getting full advance when needed. Of course running the engine too lean would cause the engine to run hotter also. How is the fuel pump pressure and volume?

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has some interesting info like a flowchart forNOx.

Were you able to check the CO and HC before the cat?

But you probably won't worry about this again until your next test. lol It sounds like your car does not see a lot of use which could indicate a build up of deposits inside of the engine which could cause problems. A nice long highway trip with the car along with some good upper engine cleaner in the tank might do wonders.

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris