Fuel milage stinks need ideas / options.

[Jeff in MN]

This is for my 1990 535i (m30) with EAT chip. Currently getting 13 mpg around town. Was getting 15 around town in warmer weather, but that is still poor.
Running 89 octane.
Engine smooth and strong
Recent valve adjustment - idles perfect.
plugs are great.
No gas smell at start.
exhaust is soot free.
I am not a lead foot.
Tested O2 sensor and reading range was .085 to .850 with an average of .445.
How what else should I check? and how can I lean this baby out?
Btw here's a pic from when I brought her home this summer.

[Derek A.]

At that mileage - I wonder what the intake valves look like. Could be all cobbled up with stuff. My car's mileage has never been wonderful. My car as 205K on it. These cars do run real fat in the colder weather.

[shogun]

your O2 sensor results seem too high.

If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts.

http://www.ibmwr.org/ktech/O2-sensor-testing.shtml
http://www.gnttype.org/techarea/ecmsensors/O2sensors.html
http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/04/f6/02/0900823d8004f602.jsp

[BillionPa]

how old are the air and fuel filters?

also, run higher octane gas.

temp sensors can stick the car in warmup enrichment mode too.

but the main thing, is the gas in MN is 10% ethanol.

if you are near 169 and rockford rd, or by hwy 101 in wayzata, there are shell stations that sell 92 octane ethanol free gas. expect a 15-20% increase in mileage by switching.

i averaged 15.7 with horrible idle and no power using 93 octane ethanolated gas, and jumped to 18.5 with perfect idle and tons of power with ethanol free.

[Jeff in MN]

temp sensors were within spec. I am pretty close to 169 so I'll have to give that a try.

[jbraswell]

If you have a chip you have to run 93 octane

[Jeff in MN]

This the 1990 with 105k. Haven't seen the valves, but intake is very clean. I had a chance to boroscope the valves on my 535is with 240k and those were definitely carboned up.

[bill g]

Does car roll along OK? I mean brakes not binding? No heavy weight in trunk?
Do you spend a lot of time sitting in traffic? Also, have you calculated fuel consumption directly from actual quantity at fill up and miles covered? OBC reported consumption could be faulty/wrong.
Some observations -
My 535i has chip and I have found different fuel octanes do not make much difference to performance or fuel consumption, although we do not have real extremes of temperature here in Melbourne Aust.
My exhaust is moderately sooty but the fuel consumption is a lot better than you are getting.
My O2 sensor output is OK I reckon, and is roughly similar to yours, presuming the figures you have stated are for full range of operation on the road, not just at idle.

Bill G

[Jeff in MN]

Does car roll along OK? I mean brakes not binding? No heavy weight in trunk?
Do you spend a lot of time sitting in traffic? Also, have you calculated fuel consumption directly from actual quantity at fill up and miles covered? OBC reported consumption could be faulty/wrong.
Some observations -
My 535i has chip and I have found different fuel octanes do not make much difference to performance or fuel consumption, although we do not have real extremes of temperature here in Melbourne Aust.
My exhaust is moderately sooty but the fuel consumption is a lot better than you are getting.
My O2 sensor output is OK I reckon, and is roughly similar to yours, presuming the figures you have stated are for full range of operation on the road, not just at idle.

Bill G
She rolls great, coasts smooth and I keep the trunk empty. Next chance I get I check o2 readings during operation.

[shogun]

Find out which pins on the ECU are for the O2 sensors. Then remove the cover from the ECU connector and connect the multimeter there and put the multimeter on your center console with elongated wire connection.
Then you can always check the voltage of the sensors.
I do not know the pin connectors on your car, just that from my 750 MOTRONIC's.

[ILoveMPower]

If you have a chip you have to run 93 octane
.

[SC David]

My winter MPG always drops by at least 2, but 13 seems too low, even for an M30.

[John B.]

My 90 535i has the Eat chip installed & runs fine on 91 octane Ethanol gas. Fuel mileage averages 18-19 around town & 23-24+ on the highway. On a recent trip down south I didn't see more then a 10% change in fuel mileage running non ethanol gas.

[Jeff in MN]

My winter MPG always drops by at least 2, but 13 seems too low, even for an M30.
like 18 -19 in town as John B. describes below. Over the Christmas break I'll be taking the AFM apart to see how it looks. Seems like my MPG meter is really jumpy, perhaps it's related. ONLY way I can think to save fuel is to NOT drive this beauty and that would be crime :-)))).