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  #1  
Old 01-28-2003, 03:34 PM
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Join Date: Sep 2002
Location: Denmark
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O2 sensor/EHA? - 300E running rich

I know this topic has been beaten to death. And i DO have read the immense amount of threads regarding this. But i still can't get i right..
My '86 300E, 178000 miles, is running WAY too rich. (~10 mpg)

Symptoms: Exessive fuel consumption, Exhaust smells of gasoline, Black soot from tailpipe, Black smoke under full throttle, and a strange 1 sec. 'surge' when i touch the gas pedal.

I haven't been able to get my hands on a multimeter with duty cycle, so i have only measured volts and miliAmps.
Warm engine - unplugged O2 sensor - measured 0,77V at idle and 0,81V at 2000 rpm from the sensor. (should be in range right?)
I followed stevebfl's advice to adjust the mixture to the lowest possible reading (volts) and got -0,1V..! -engine still running well.
I reconnected the O2 sensor and measured mA at the EHA. -And the reading was all over the place. From -15mA to +10mA.

In the process i turned the allen screw about quarter of a turn CCW. So no matter what the readings say, the mixture must be leaner now, right?

What i DID get out of all this, was a jumping idle at 750 rpm where i had a steady idle at 500 rpm before.

I simply don't get it...

Freestyler
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'86 300E optically converted to '95 E300 (Sold)
-Blauschwarz on silver
-Black leather
-17" AMG & 15" AMG for winter
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  #2  
Old 01-28-2003, 04:03 PM
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Misery loves company

Right now, I'm in the boat with you. I have the same symptoms, although your readings don't tell me much. Try this, remove the air filter and depress the airflow plate gently as far as you can. Get a focused beam flashlight and look inside the air chamber. It should be dry in there. If not, then you probably have a leaking seal on the fuel distributor plunger. Also look carefully at the fuel pressure regulator. Mine is leaking fuel out of the front section. The end with the vent tube. That will also waste gas and causes driveability problems.
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  #3  
Old 01-28-2003, 06:02 PM
inspector1
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Re: O2 sensor/EHA? - 300E running rich

Quote:
Originally posted by Freestyler
My '86 300E, 178000 miles, is running WAY too rich. (~10 mpg)

At the bottom you have ' 86 300E CONVERTED to 95 300E' what do you mean by this? If you have swapped engines, it may play a role in diagnosis

Symptoms: Exessive fuel consumption, Exhaust smells of gasoline, Black soot from tailpipe, Black smoke under full throttle, and a strange 1 sec. 'surge' when i touch the gas pedal.

This could be many things, fuel pressure regulator, bad plugs, bad wires,burned valves,bad valve guides etc

Warm engine - unplugged O2 sensor - measured 0,77V at idle and 0,81V at 2000 rpm from the sensor. (should be in range right?)

No, O2 Volts > .45 is rich


More info on what the 'conversion' means will help
Freestyler [/B]
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  #4  
Old 01-28-2003, 08:25 PM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
It sounds like you have a marginal cylinder (weak injector, vacuum leak, fuel distributor problem), and when you leaned the mixture, you caused a lean misfire.

FWIW, I was getting .23V from my sensor at idle.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #5  
Old 01-29-2003, 01:04 AM
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inspector1:
The '95 conversion didn't include the drivetrain. Engine is the original '86.

Can anyone explain how it's possible that i could get the reading -0,1V from the O2 sensor when leaning the mixture -and still have a running engine??
Is the mixture too lean now? Will i fry my valves?

Freestyler
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Never criticize someone until you've walked a mile in his shoes. That way, when you do, you're a mile away -and you have his shoes!


'86 300E optically converted to '95 E300 (Sold)
-Blauschwarz on silver
-Black leather
-17" AMG & 15" AMG for winter
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  #6  
Old 01-29-2003, 09:52 AM
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I find it hard to see how a lean mixture can produce tailpipe soot. I still think you're getting raw fuel dumped in there from somewhere.
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  #7  
Old 01-29-2003, 10:21 AM
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Join Date: Apr 2000
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Agree with the Cap'n. If you have a car that starts running rich (or lean for that matter), then adjusting the mixture is not the solution. There is another problem that you need to find and fix.

What I have learned from all the posts on this subject and my own experience is that you make very minor adjustments to the mixture to compensate for component wear, or to re-calibrate the system after a major component has been replaced or repaired.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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