I moved from NY to California this year and just tried to smog my 420 SEL with 560 motor and failed by a huge amount. Readings are:

HC (PPM)

idle: Max=120 measured= 455
2500 RPM Max=140 Measured= 125

CO (%)

idle: Max=1.00 measured= 9.99
2500 RPM Max=1.00 Measured= 1.80

Anyone have any idea as to what might cause such high readings? BTW, the engine runs great. Idles smooth, has no hesitation and has lots of power.

Thanks for your help.

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1988 420 SEL
1991 420 SEL with 560 motor
1993 Miata

It's running way too rich. Assuming you still have the original electronics present try testing the duty cycle as described in many threads here, also perhaps try adjusting the air/fuel mixture while doing this to see if the duty cycle reading can be brought close to spec. The catalytic converter can't do its job at this time since there is virtually no free oxygen present in the exhaust stream with the way the engine is currently running.

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Erich Loepke
2010 Ford Focus
Currently Benz-less

Davestx,

I'm not too familiar with your model, but the oxygen sensor might be the culprit. I'm not sure if it would read quite that high, but still it's a place to start. What year car is this? early 80's cars that were sold in California had extra emissions stuff than cars sold in the other states, and were equipped with air pumps (also called smog pumps) that pumped air into the exhaust to thin it out. California cars also had EGR valves on the exhaust. In the early 90's, they started putting these things on all the cars. California has way higher emissions standards than NY does, and it seems like your car might be set up for NY rather California. Check into that.

Good luck

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Streetside: 1987 Mercedes 300E Petrol Blue/Green
2014 Ford Mustang Grabber Blue
1999 Ford Ranger Green

Dockside: 1968 Eltro 17
1985 Silverton 34C

The car is a 91 and is a 50 state car. It has all of the emissions gear in place including a smog pump and EGR valve. I have decided to bring it in to my mechanic tomorrow and let him give me an estimate to get it into shape. Thanks for your replies.

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1988 420 SEL
1991 420 SEL with 560 motor
1993 Miata

I guess I should have read the bottom of your post, where it says the models and years of your cars! Good luck anyways. Please post what the problem was, I am curious to know!

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Streetside: 1987 Mercedes 300E Petrol Blue/Green
2014 Ford Mustang Grabber Blue
1999 Ford Ranger Green

Dockside: 1968 Eltro 17
1985 Silverton 34C

For sure the car is WAY too rich, have you tries adjusting the mixture so the O2 sensor can have control of the system...closed loop

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Also don't forget the basic stuff like a new air filter...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



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