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1990 500SL
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I recently purchased a 1990 500SL from Michigan. I live in Ontario and thus require an emissions test (1988 and newer). I took it for an e-test an it failed miserably (HC 800 vs 200 for a pass, 7.18 CO vs 1.00 for a pass). The test garage suggested that I needed to take the car to the Mercedes dealer.
I showed the results to my local mechanic and he said that the results showed a faulty catalytic converter. I took the car to my exhaust guy and he took me to his emissions tester and he agreed that it was a bad converter. I changed the catalytic convertier with no improvement in results.
O.K. so off to the Mercedes dealer I go. They diagnosed the problem as a faulty 'hydraulic actuator of fuel distributor'. $1677.38 later, I got a passing e-test but just barely (HC 182, CO 0.83). And as I found out from a VIN number mistake and required retest, the dealer adjusts the fuel for the test and then readjusts for proper running.
Now this is not a high mileage car that has reason for failure. It has 22,000 original miles. Michigan does not have e-testing so the previous owner would have had no idea that the car wouldn't pass.
Were these cars marginal for emissions even when new?
Can low emissins just not be able to achieved using a mechanical fuel injection system? ( my 2000 GMC with 160,000 miles scores HC 20 Co 0.02)
Can anything be done to improve the e-test numbers?
 

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2005 SLK350, 91 300SL with Pano Top, 04 S500, 2015 Tesla Model S
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2,084 Posts
Check if anyone has fiddled with the mixture adjustment. You can do this by checking if the ball bearing ball has been drilled out. The engine should run at a 50% duty cycle. This can best be measured with an Oscilloscope.
 
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