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Old 07-27-2002, 10:16 PM
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300e Poor Gas Mileage

Wife yelling at me because the 1989 300E is getting less than 10 miles a gallon. It's been running great since head job in January when I put new plugs in it. Also put new injectors in about 20 K ago. Would the Oxegen Sensor cause poor mileage? I know it had not been changed for years.

I'd love suggestions

Mike V
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Old 07-27-2002, 10:47 PM
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Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
A bad O2 sensor can cause drastic fuel mileage drop.
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

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Old 07-31-2002, 10:49 AM
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where wolud u find the 02 sensor?
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Old 07-31-2002, 12:03 PM
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yal yal is offline
Join Date: Oct 1999
Location: New York, Long Island
Posts: 2,704
Somewhere screwed in around the exhaust manifold piping through to the cat. Some cars have 2.
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Old 07-31-2002, 01:05 PM
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There are two exhaust manifolds. One of the two pipes running from them to the catalytic converter has the sensor. It's just ahead of the cat. The wires to the sensor feed up to a connector that is under the curb side carpet in the footwell for the front seat.

Remember to use anti-seize paste when installing the new sensor.

The Bosch sensor lists for $170 but is sold here (Mercedesshop) for $128.
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Old 07-31-2002, 04:53 PM
Join Date: May 2002
Location: Columbus, OH
Posts: 44
Just replaced the O2 sensor on my 89 300E 136K last weekend. It is screwed in to the top of the exhaust pipe in the transmission hump. The cable goes through a grommet on the passenger's side of the hump and connects under the carpet.

There are some threads here talking about a Bosch universal which is the equivalent of the OEM but can be purchased in any parts store for $60. I ordered a universal by Walker on the web. Can't remember the site.

For mileage I get around 20 city and 26 highway, but in the city I do a lot of downshifting to brake and accelerate.
Jim Wiggin
Columbus, OH
1989 300E
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