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General E46 Forum
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Old 02-16-2015, 03:14 PM   #1
evanr614
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14 mpg..? :(

So thanks to jfoj I was able to swap out my fuel pump with a VDO one for 123 shipped to my door, came in two days. We've had some really cold days following the day I did this repair and as far as I can tell it has corrected my slightly erratic cold start idle! We have -10 degree wind chills in Ohio today and granted I didn't really let me car heat up before I left my driveway. So far so good, no cold idle dips/stalls. I'll have to do a test another day to confirm.

However I have noticed the mileage my car is telling me i'm getting is terrible I might as well be driving a Durango. It doesn't really feel like it eats up fuel, but I don't drive that much during the winter anyways. Could the reading be inaccurate? I've now replaced my fuel filter and pump. Would a fault MAF degrade my gas mileage that much? Autotrans fluid, oil change, CCV refresh, and a new battery ar next on the list to do for the next month or so.
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Old 02-16-2015, 03:17 PM   #2
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Calculate MPG manually and see for yourself.
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Old 02-16-2015, 03:24 PM   #3
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Originally Posted by WDE46 View Post
Calculate MPG manually and see for yourself.
Was going to do this the next time I fill up.
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Old 02-16-2015, 03:37 PM   #4
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Tire pressure ?

For every drop of 10 degrees F, equals a 1 psi drop in tire pressure. So if you haven't checked them recently they could be quite low.



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Old 02-16-2015, 03:39 PM   #5
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Tire pressure ?

For every drop of 10 degrees F, equals a 1 psi drop in tire pressure. So if you haven't checked them recently they could be quite low.



Rob43
They were filled maybe two weeks ago, but it has been cold. I'll get a gauge on them tonight.

Thanks
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Old 02-16-2015, 03:44 PM   #6
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Use the OBC to watch and track the Average MPH, not MPG.

You can watch MPG on the OBC, but MPH is FAR more USEFUL.

Below an average of 20 MPH, expect this to be close to your MPG!!!

What is likely happening in your situation is the following:

1. The engine may not be running at the correct temperature due to a soft thermostat and/or short trips.

2. It is very cold out, you are likely starting your car and letting the engine idle for the car to warm up. Keep in mind for every second the engine idles while the car is NOT moving you will get EXACTLY 0 MPG!

3. Winter blend fuels could factor into reduced MPG.

4. Tire pressures have likely dropped 4-5 PSI from when you last checked and inflated them.

5. Do you have different wheels/tires on for the Winter?

6. Traffic may be moving slower and may be heavier if there is snow blocking exit ramps, entrances into shopping centers, parking spots may be free and far between with a lot of parking lot circling and in general just more traffic due to less roadway because of excess snow on the road.

But watch the Average MPH, reset it for each tankful and if it is below 20 MPH, this is likely your fuel economy problem.
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Old 02-16-2015, 04:12 PM   #7
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14mpg is still a bit low, isn't it? My commute nowadays is mostly non-highway and my overall mpg has never fallen below 22ish. Even in pure city driving I'm usually pretty close to or slightly above 20mpg.
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Old 02-16-2015, 04:23 PM   #8
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If the car is idling a lot, 14 MPG is totally acceptable.

Until you know what the Average MPH is, you would never know how much idling the car is doing.

My wife drove in heavy city commuting for years in her E46, car would rarely show an average MPH over 19, usually around 18 MPH.

This is because the traffic conditions force you to sit still at a traffic light for about 30% of the commute. The rest is just trying to get up to speed.

Her 330ci would usually average about 18 MPG on the OBC for Fuel Economy, pretty much matching the Average MPH.
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Old 02-16-2015, 04:26 PM   #9
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If the car is idling a lot, 14 MPG is totally acceptable.
Fair enough. I wasn't disagreeing with you, I was just kind of surprised since I've never seen my fuel economy fall that low over a variety of driving conditions.
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Old 02-16-2015, 04:58 PM   #10
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Fair enough. I wasn't disagreeing with you, I was just kind of surprised since I've never seen my fuel economy fall that low over a variety of driving conditions.
14 MPG is very low, but if the engine is running and the car is not moving this equals 0 MPG. Starting the engine and letting the car warm up is going to kill the Average MPG and MPH. To raise a 0 MPG average to say 20 MPG Average there would need to be a lot of highway cruising to bring or offset the average upwards.

I find it totally pointless to even speak about fuel economy because one persons City traffic is very different to another persons City traffic. This is where I find the Average MPH does not lie and will clearly help someone understand now much idling the car is doing and what kind of City traffic conditions they are dealing with.

If the OP comes back with an Average MPH of between 14-16 MPH, then this is not a condition to even discuss Fuel Economy.

Fuel Economy is usually expected and expressed at highway speeds 50-70 MHP average speeds. So not even worth the breath to worry about anything until we fully understand the Average MPH per tank full of fuel.
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Old 02-16-2015, 06:50 PM   #11
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Originally Posted by jfoj View Post
14 MPG is very low, but if the engine is running and the car is not moving this equals 0 MPG. Starting the engine and letting the car warm up is going to kill the Average MPG and MPH. To raise a 0 MPG average to say 20 MPG Average there would need to be a lot of highway cruising to bring or offset the average upwards.

I find it totally pointless to even speak about fuel economy because one persons City traffic is very different to another persons City traffic. This is where I find the Average MPH does not lie and will clearly help someone understand now much idling the car is doing and what kind of City traffic conditions they are dealing with.

If the OP comes back with an Average MPH of between 14-16 MPH, then this is not a condition to even discuss Fuel Economy.

Fuel Economy is usually expected and expressed at highway speeds 50-70 MHP average speeds. So not even worth the breath to worry about anything until we fully understand the Average MPH per tank full of fuel.

It's reading an average speed of 24 mph
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Old 02-16-2015, 07:32 PM   #12
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Originally Posted by evanr614 View Post
It's reading an average speed of 24 mph
When was the Average MPH last reset?

It needs to be reset every fill up.

And do you know for sure there are no fuel leaks, if the fuel pump was replaced and the seal not properly installed the fuel tank will leak when full to about 7/8ths of a tank.
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Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

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Old 02-16-2015, 07:40 PM   #13
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When was the Average MPH last reset?

It needs to be reset every fill up.

And do you know for sure there are no fuel leaks, if the fuel pump was replaced and the seal not properly installed the fuel tank will leak when full to about 7/8ths of a tank.
It was reset probably 2 drives before I last got gas. But I was very attentive to making sure I got the fuel pump seal seated properly. I may double check it if I get a lucky warm(er) day here soon. I got gas today, didn't fully fill up the tank though. I'll make sure to reset it when I fill it up next. The mpg did move to 15.5 from the last time I looked at it. To be honest I never looked at my mpg too often, usually had it set to my clock or check the ranged left on my tank which has always seemed to be really reliable. I've Never tested its limits haha
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