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Old 03-19-2001, 01:15 PM
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I have a 85 190E 2.3. Want to know how I can adjust the fuel-air mixture myself - everytime I get the car back from the shop, they set it too rich - fuel mileage is low. so I have to go back and get the mixture leaned out. What specific tool do I need? Is the mixture screw the one right in the middle of the air filter housing in the hole? Also, what damage can it do to my car if I let it run rich?

Thanks very much for all your help.

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Old 03-20-2001, 02:37 PM
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Would anyone please reply to my post and help me out?

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Old 03-20-2001, 05:01 PM
Registered User
Join Date: Feb 2001
Location: BC, Canada
Posts: 378
I'm not a tech, so take this advice for what it is worth, (not much).
Yes, the hole you are refering to is the mixture adjust point.
There may be more to adjust that I don't know about yet. To adjust,
you need a special, long allen key wrench. I don't have one so
I can't tell you how long. I think that the Merecedes CD shows the
tool with it's part number and possibly it's length.
Don't change the setting much; you don't want to make it worse.
As for running rich, as far as I know, you can't hurt much.
You likely work the catalytic converter more and have higher
1967 250SL
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Old 03-20-2001, 05:41 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
To adjust requires a 3mm allen wrench. Turning the adjustment clockwise richens, ccw is leaner. To know what you are doing there are two methods.

One involves monitoring the integrator on the #3 pin of the diagnostic socket on the left fender. This will require a faily good multimeter with a duty-cycle range.

The second and more informative way is to monitor EHA current with a cheap multimeter (one with a 2amp scale).

Both methods are described in the DIY article "evaluating engine controls". The value you are going for on an early 190 is 8ma with an oscillating reading (plus a ma or two and minus a ma or two). Remember that a dead (or disconnected - to verify your system try disconnecting the O2 sensor and you should get 8ma EHA current or 50% duty cycle on the integrator) O2 sensor will give a fixed reading of 8ma when warm (so it can't be adjusted by either method - both methods monitor the closed loop lambda cycle).
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 03-20-2001, 06:26 PM
Posts: n/a
Thanks for your responses, Steve and Vaughn. I was reading somewhere that for moving the fuel misture screw, I should press down with the wrench - is that true?

One more issue. How harmful is it for the car if its running rich (fuel consumption up by 10-15%) - in terms of carbon build up in the engine, and clogging up of the cat. converter. My mechanic said - "Oh its fine, it won't hurt your car". But I'm not so sure. Any insights/experiences would be greatly appreciated.

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