Another MPG question thread

[anthonymax007]

I've been tracking my MPG's for the past couple months. Not much highway driving, I'm shifting around 3 or 3.5k rpm's, and I've got a stretch of road that has quite a few stop signs. I'm averaging around 16-18 mpg. This sound's horrible to me. Is this just a matter of shifting at too high of revs, or is there something else I need to look into? The car has new spark plugs, wires, and a new fuel filter as well.

[Poorboyz]

I'm a spirited driver and I'm getting 19.5 on city.

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[bmwman91]

Your mileage is pretty low. I'd imagine that it is from a borked O2 sensor, or that is what it USUALLY is anyway. No seized brake calipers or dead wheel bearings?

[anthonymax007]

Brake calipers are fine, not sure about the wheel bearings. How can I tell? I should order an O2 sensor and switch it out. Can't imagine it's been done within the last 50k miles.

[brianf408]

16-18 mpg is very low. I usually average 28 mpg with city/highway driving. Shift between 3.5k and 4k RPMs, and usually get pretty heavy on the gas getting on the highway. Been a little worse lately, trying to track down the issue. Leaning on O2 sensor or fuel pressure regulator.

Checked the more obvious things? Tire pressure, wheel bearings, brake calipers, alignment, etc? Stock differential in the car or lower gearing?

[anthonymax007]

Just did the stomp test, code 1444. Would a bad O2 sensor throw a 1221 or 1212 code?


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[anthonymax007]

Tire pressure and brake calipers are fine, last alignment was about 5k miles ago, stock 4.10 differential. I'm not sure how to diagnose the wheel bearings or fuel pressure regulator though.


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[bmwman91]

Sucks tossing money at a problem, but the O2 seems like the obvious issue. Without a wide-band O2 sensor it is hard to tell what your mixture looks like. You can always go to a SMOG station and have them run the sniffer (it should be pretty cheap to just have them do that without submitting the data or anything) and the values from that can be used to calculate your AFR.

[anthonymax007]

Tossing money does get a little frustrating, but it's a necessary evil. I'll order a new O2 sensor, general consensus seems to point towards that. The car is running nicely, aside from the poor fuel consumption, so I'm not suspecting vacuum leaks or anything like that. Thanks for all the input.


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[roguetoaster]

How about verifying timing? You could also check function/replace/rebuild the AFM.

A quickie test to see if you have suspect wheel bearings is to find a well paved hill and coast down, both listening for noise and feeling for drag.

As far as the O2 sensor you can easily get away with getting the least expensive universal from a reputable brand and splice it in. Even accounting for heat shrink, nice connectors and time it's a worthwhile savings.

[golde30]

my old m20 got about 16-18 in the city, but i live in a city full of hills and traffic...

[TobyB]

Even when I'm having a shitty month, only doing cold, in- city commutes and
generally hating life
(which means, pedal's on the floor most of the time)
the lowest I've seen is 24.
It's usually 26- 28 mixed driving, and I don't shift until I see 4, minimum. Hell,
it doesn't make any power below 3.

If it's running well, yeah, oxygen sensor. They're consumable anyways...
Also, find the bentley and test the temp
sensors (there are 2- intake and water) because if they're out of spec, they'll cause
high consumption without necessarily throwing a light.

t

[Bmr]

I am on the pedal all the time while driving. I have a 4.44 lsd and get 4 mpg more than you. Did you happen to touch the throttle position screw lately?

[CHIF8008]

technically for the best MPG you should be shifting at 2.5k but im usually shifting at 3k

deff sounds like you are not running right.

[Gerta]

Even when I'm having a shitty month, only doing cold, in- city commutes and
generally hating life
(which means, pedal's on the floor most of the time)
the lowest I've seen is 24.
It's usually 26- 28 mixed driving, and I don't shift until I see 4, minimum. Hell,
it doesn't make any power below 3.

If it's running well, yeah, oxygen sensor. They're consumable anyways...
Also, find the bentley and test the temp
sensors (there are 2- intake and water) because if they're out of spec, they'll cause
high consumption without necessarily throwing a light.

t

26-28 is what I get around Seattle as well. The new engine I'm hoping with push that up into the 30+ range.