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Nope, unless it has an M5 engine, but then... (archive)

[ Follow Ups ] [ 5-series (E28) Message Board ] [ Msg. Board FAQ ]

Posted by JamesM on January 30, 2001 at 10:05:18:

In Reply to: Is 17mpg OK? posted by Artem Grigoryev on January 30, 2001 at 09:04:31:

But then you'd have 250+ HP and you wouldn't complain about lack of power. Sounds like the car is running too rich for one reason or another. Too rich results in reduced power. I've had bad O2 sensors do this. One got fried in a deep puddle, and it caused the car to get about 6MPG!! I unplugged the O2 sensor, and the mileage shot up to a whopping 18MPG. I replaced the O2 sensor with a Bosch for a 1987 5.0L Mustang--$50 from your local parts store, and in stock! I had to solder the old connnector from the OE BMW O2 sensor (also made by Bosch) but I saved $80. The mileage went up to 23-25MPG. That's good, because I have a 3.73:1 diff, which lowers my fuel economy by about 15%.

So in short, check your O2 sensor. If you have a multimeter, consult your Bentley manual on how to check the sensor.

Also, there are 3 solder joints inside the ECU (engine control unit) that go bad over time. Open it up and you'll see a large round transistor on the side. It has 3 jumper leads soldered to the board. The joints on the board come loose, and that weakens the spark. This KILLS the power, and you'll open up the throttle more to compensate, hence the poor fuel economy. Common problem among 80s BMWs. Resolder with good lead-free solder. Radio Shack sells a small tube of 94% tin 6% silver rosin core solder for about $2. A 15/30W switchable soldering iron is $10.

Another problem may be your air-flow meter crapping out, but that is less likely than the other two problems. If so, you'll need a good used one to borrow for comparison.

Check these and let us know what you find.

James
[email protected]
88 M5
88 M3
83 535i


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