1G high CO | Stock 1G

[theodor]

Hey there dear DSM people,

firstly i‘d like to mention that I read up on all kinds of posts here on the forum and elsewhere on the World Wide Web, but I still decided to post, as they didn’t help me to solve my problem.

I am Theodor from Germany and a proud owner of a white 1991 1G.
I imported the car from Switzerland (there are not many DSM‘s around here). It’s bone stock and has had one owner for the past thirty years.
I drove it back to Germany around 1000km‘s (~600 miles) and it runs great, has power, good idle, starts right up.

I did all kinds of regular maintenance before trying to get it registered.
I changed the oil, spark plugs, ignition cables, set the ignition timing correctly, valve cover gasket, gear oil change, air filter.

My only current problem is that it doesn’t pass emissions.
I drove it some 20km‘s on the highway to the emissions testing station, so the car was definitely warm.
The CO value is way off at higher rpm‘s.
To help you read the German report:

CO at idle (800rpm) 0.339
here it passed, the limit is 0.5

CO at higher rpm’s (2720rpm) 0.828
failed badly, the limit is 0.3

Lambda value is 1.01

I got an original Bosch O2 sensor from the US, which I didn’t yet replace and just in case a catalytic converter which I found a good deal on. (Got to these conclusions as other posts on the forum were suggesting it)

I kind of have an understanding that my car must be running quite rich, and I can smell that when I’m next to it. What is weird though is that the gas mileage I get is totally fine.

Is my MAF potentially broken and the ECU thinks that it needs to supply way more fuel than actually necessary?

For any kind of help I’d be very grateful. Thanks

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[dwb]

Only time in 25 years I failed emissions is when my o2 sensor died. I'm still running the original cat with 280k miles, too.
FYI, Here's my latest test, which appears to be measured in a different metric than yours (GPM vs %vol) https://www.dsmtuners.com/threads/1991-tsi-awd.540276/post-153906077

 

[steve]

Same here, everytime I failed it was due to a slow responding O2 sensor. Last time I tested it was without a catalytic converter and it still passed although HC levels were pretty high but under the limit.

 

[theodor]

Hey guys,
thanks for your quick response. Got both the o2 sensor and catalytic converter swapped. Finally got the emissions inspections to pass.

But it was tough though, I needed to really really warm up the catalytic converter and then I got it to pass. Otherwise no chance. Pinned it at like 5k rpm for half a minute right before the emissions testing.

I have the feeling it would have passed with both old components aswell, as I got bad emissions results with the new ones once. Key seemed to be that the catalytic converter needs to be really hot.
Final passed results in screenshot.

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