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Old 04-28-2003, 10:09 AM
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w124 low gas mileage

I have a 1991 300e. It has around 130k on it and it gets low gas mileage like 250/tank when doing half city half freeway commuting.

What are the things i should check, adjust to increase the gas mileage? I.e. replace o2 sensor, check gas mixture etc, tire pressure, idle rpm? thanks

Last edited by whair; 04-28-2003 at 12:07 PM.
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Old 04-28-2003, 10:15 AM
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250 miles/tank? mpg may ellict more meaningful responses.
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Old 04-28-2003, 10:22 AM
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So that's around 15mpg. seems pretty bad huh?
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Old 04-28-2003, 11:32 AM
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wow...that is great...I wish I had that sorta mileage...
1995 black pearl/black Mercedes-Benz E420 :
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Old 04-28-2003, 12:09 PM
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15 mpg isn't good for a 6-cyl W124...unless you tow a camper uphill on a regular basis...

Yes, there are a number of factors that can impair fuel efficiency.

My first question is how is your engine's performance? Does it idle and run smoothly?

Fuel injectors may get clogged over time, and that will have a drastic effect on fuel consumption. Do you smell any gas fumes when on the road? Check for fuel line leaks as well. I had a fuel line give up a few months ago. Didn't leave any puddles, but gas mileage was horrendous!

A bad O2 sensor would set off a code. Check for codes first.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
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Old 04-28-2003, 12:27 PM
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On my '95 124 mixed city/commute (stop and go) driving, mileage varies from 15 to 18 MPG. On the freeway, however, it gets ~24 MPG even with average speeds of 80+ MPH.
Glen Tokuhara
Beauty & the Beast and the wagon that could!
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Old 04-28-2003, 12:53 PM
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The engine seems to run fine. sometimes the idle is really high like around 1.5-2 when in park, then it drops when put in drive. I dont' smell any gas and don't have any gas puddles or anything.

It the fuel injector & gas line fixing a major repair? thanks
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Old 04-28-2003, 01:14 PM
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If this is any help, our '91 300E gets 20-21 MPG with combined 50/50 city/highway driving. When on the highway it is around 70 - 80 MPH. The best MPG was 24.5 at a steady 65 MPH. The worst was 17 MPG in the winter doing all around town driving. The car has 206,000 on it.

A good injector cleaning way to go is to put at least one bottle of Techron Fuel Injector cleaner in less than a full tank of fuel. I have done two before with excellent results. It is recommended that you also change the oil shortly after doing this.

Also I run 32 PSI on the tires, cold. A little firmer ride but much better handling and a little better MPG.

Has it always been this way? How do you drive? Hard, gently? Also consider that your O2 sensor could be on its way out.

Keep us posted,

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'95 E320 Wagon-Went to Ex
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Old 04-28-2003, 03:09 PM
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Location: Houston, Texas
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Try all of the above suggested, and as GBenz stated, check fuel lines for leaks, around the fuel filter and pumps. Mine were leaking for awhile, but since fuel evaporates so quickly and the setup is located under the black cover (just forward of passenger rear wheel, underneath) I never smelled it.

The copper washers lose their sealing ability over time so if they're leaking, tighten them down, or better yet, replace. Good idea to replace your fuel filter while you're down there.

When was the last time your car passed an emissions test (if your state requires it)?

Good Luck
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi
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Old 04-28-2003, 09:12 PM
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Sounds like my car.

O2 sensor was bad.

Get yourself a multimeter with a Duty Cycle function. Sears has a good one for $30.

I would invest in the CD manuals as well. Check out the DIY link above. 124 engine controls. Good article.

Good luck,
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Old 07-14-2003, 11:45 AM
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Vacuum Tube was broken which caused high idle, and there's some micro switch on the gas pedal which was broken. runs much better now.
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