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american 1986 300E 3.0l
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107 Posts
Discussion Starter #1
still chasing this bad gas mileage.
but now it is really wierd

put on new rear muffler and tail pipe a month ago,just happened to see black at the tail pipe. looked in the tail pipe and it is very sooty, which would mean running rich.
now this is the wierd part in the summer i went through tank a gas in 5 days and did not do anything different. so i lowered my air fuel ratio down to 20% on a multi meter(from 50%) with freq that even reads the % now i am getting about 2 weeks on a tank of gas.
so after lookin at the tail pipe i took out my spark plugs and they are white or with a touch of brown and i think #1 cylinder is leeking coolant.


so why is it running rich out the back but running lean at the sparkplugs
 

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89 300E; 00 E320
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2,515 Posts
Hard to believe that you would be in adjustment at 20%. Your duty cycle should be within 10% of each other at idle and at 2500 RPM's. And that usually happens around the 50% duty cycle. Each engine would be a little different, but I can't imagine it being withing tolerance if the duty cycle is not between 40% and 60%.

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1231077-fuel-mixture-adjustment-4.html#post4454281

You may want to check your O2/lambda sensor too.
http://www.benzworld.org/forums/w124-e-ce-d-td-class/1557913-oxygen-sensor-lambda-sensor-voltage-testing.html
 

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Registered
american 1986 300E 3.0l
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107 Posts
Discussion Starter #3
so i should be good now.
i just do not understand the rich out the back but lean at the plugs.
i'm old school carb, lean you get white at plugs and no black out back or rich u get black at plugs and black out the back.
this is where i was in the summer but had shitty gas mileage,that is the only reason i went lean.
so if i get shitty gas mileage what should i be looking for.
(i have changed all my vacuum connection under the hood and even to the economy gauge at the cluster)
like i said this fuel injection stuff is new to me
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,745 Posts
New O2 sensor then re-adjust your air/fuel ratio. Leaned out as far as you state, it's a wonder the car will start.

Jayare
 

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american 1986 300E 3.0l
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107 Posts
Discussion Starter #6
hey there jayare
the car started up good some days would be worse.
it never started in the winter when i got it(turn over and over till the battery died)
took the car off the road back on in the spring then changed the coolant temp sensor
now it started up in the winter.

also would that sensor being giving false readings. if i can recall that sensor does 2 different things(computer and fuel/ignition)
 

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1991 300E
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601 Posts
i now have a gps and going to use that once i figure out how to use the fuel calculations
That seems an overly involved way to calculate MPG or KmPG(l?). Why not simply use the odometer and a receipt from the filling station?
 

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american 1986 300E 3.0l
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107 Posts
Discussion Starter #9
my odometer has never worked.
well accept for 1 day when i took it apart to fix then broke again,then i just gave up
 
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