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Old 03-17-2008, 06:22 PM
Registered User
Join Date: Mar 2008
Posts: 3
High NoX emission

My 1989 300SE has been doing swell at 124,000 miles...still uses almost a quart of oil in 3,000 miles!

In Atlanta we must have emissions tested every year. I noticed last year, the Benz passed by ONE point on the NOx scale.

In the past on another car, someone told me that when the NOx is high, the EGR is bad/failing.

I put a can of 44K (made by BG Products) in 10 gallons of premium gas as recommended by a friend--I have no connection to the company. He said this would help to clean out the carbon in the head, along with a 100 mile run on the interstate.

Question: If after this "treatment," the Benz fails on NOx, what do I try?

Thanks for your help while keeping this "good one" running for a long time.

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Old 03-17-2008, 06:44 PM
Registered User
Join Date: Feb 2003
Location: Ontario, Canada
Posts: 3,160
IF you fail, you need to look at:
1. EGR Valve
2. Fuel mixture ( too lean )
3. Catalytic converter.
2007 C 230 Sport.
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Old 03-18-2008, 01:56 AM
Hit Man X's Avatar
Join Date: Sep 2004
Posts: 9,087
Thumbs up

1989 did not have EGR on the M103 from my memory... that was the 1990 model year and after.
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.
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Old 03-18-2008, 09:41 AM
david s poole
Join Date: Mar 2005
Location: dallas
Posts: 1,822
one easy trick for passing a car with marginal nox[assuming you have corrected a lean fuel condition] is to pump up the rear tires to about 40psi.when a car sits on the dyno because of two rollers it has two bags on the tires and it takes power[extra push on accel]to make those bags move around the wheel.40psi should get you through.
David S Poole
European Performance
Dallas, TX

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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Old 04-08-2008, 02:03 PM
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Join Date: Mar 2008
Posts: 3

Thanks to Manny, Hit Man X, and David. After replacing air cleaner, running a can of 44x in 10 gallons of premium, replacing the spark plugs,
putting 40 lbs of air in the rear tires, and driving 125 miles on the expressway, it passed by 6 points--much better than last year's pass by one point.

The plugs were Champion...dunno who put those in! The deposits were built up, and the gaps wide.

The local Benz dealer had the right Bosch number H 9 DC non-resistor. I spent two hours looking on line to no success. Another hour calling local parts suppliers also brought no success...but when I called RBM of North Atlanta, they said, "Of course we have those!" The service manager drives a 90 300E and said, "That's the only plug to use." They cost $2.19 each.

Again, thanks!
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Old 04-08-2008, 03:02 PM
Dee8go's Avatar
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Join Date: Apr 2006
Location: The People's Republic of Arlington, VA
Posts: 7,191
That BG stuff is pretty good. That's impressive, moving 5 points on the NoX scale by doing those particular things. I'm going to remember that!
" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

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1998 Lincoln Continental - Sold
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Old 04-09-2008, 09:34 PM
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Join Date: Aug 2007
Posts: 66
Thankfully I live in the Boonies.. no emissions testing here... yet..

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