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General E46 Forum
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Old 08-10-2008, 09:51 AM   #21
andry
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Make sure:
- air and fuel filters are clean.
- plugs and wires are good.
- tire pressures is good.
- drive between 2500rpm and 3500rpm.

hope this helps.
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Old 08-10-2008, 10:34 AM   #22
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I'd second the O2 sensors. It's possible for them to degrade enough to lower your mileage but still not throw a code.

Does anyone know of a good way to check O2 sensor functionality, besides the "if they're old, replace them" mantra?
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Old 04-22-2011, 05:25 PM   #23
henryshih
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My 2001 3251 wagon just runs 18mpg, about 20miles daily local drive, i think it's really bad with gas hits almost 4.35 a gallon now.

i do have po365 eroor code on, which is (i've heard from other posts) exhaust camshaft position sensor is bad. anyone know this sensor does affect mpg..??

how to improve mpg ..??

i forget to say my wagon just past 58k miles.....



thanks,

Last edited by henryshih; 04-22-2011 at 05:27 PM.
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Old 04-22-2011, 05:33 PM   #24
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Driving habits are the single most effective thing you can change if you want to improve fuel economy. Slow down a bit, apex your corners, stay off the brakes, etc.


How well is the car maintained? Check for vacuum leaks, change your plugs, your fuel filter, O2 sensors, air filter, etc.


And then the mods, which I presume is what you were trying to get at. Headers may help a little, but not nearly as much as the two above mentioned categories.
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Old 04-25-2011, 12:29 AM   #25
henryshih
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mpg

I think my driving habit is not bad, i rarely rev over 3-3.5k rpm and i know how much you lose everytime you step on brake.


This morning, i spent awhile check all 6 spark plugs and i found most of them were wet of gas and oil ( i guess). I think this is why my fuel efficiency is so bad, too much gas were injected. i heard other thread was saying this type of plugs last at least 100k miles, mine just turn to 58k, so i brushed clean with steel brush and air down and put them back, i hope poor mpg is not from these plugs. I had changed air filter last summer when it has 52k and i double checked it was not dirty. I don't know about fuel filter, i may want to change it later. I dont know about O2 or vacuum leak. i dont get error code other than po365, also misfire

And i also checked exhaust camshaft sensor, it wasn't so hard to take out. I am getting one from

http://cgi.ebay.com/ebaymotors/ws/eB...m=120675610881

it's just 31.59 with o ring plus 8 dlls shipping, is this reliable one..??? price is not bad though...

I will post the result after i replace cps, I hope this is the main cause of poor mpg...

thx,

Last edited by henryshih; 04-25-2011 at 12:32 AM.
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Old 04-25-2011, 12:39 AM   #26
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Quote:
Originally Posted by henryshih View Post
I think my driving habit is not bad, i rarely rev over 3-3.5k rpm and i know how much you lose everytime you step on brake.


This morning, i spent awhile check all 6 spark plugs and i found most of them were wet of gas and oil ( i guess). I think this is why my fuel efficiency is so bad, too much gas were injected. i heard other thread was saying this type of plugs last at least 100k miles, mine just turn to 58k, so i brushed clean with steel brush and air down and put them back, i hope poor mpg is not from these plugs. I had changed air filter last summer when it has 52k and i double checked it was not dirty. I don't know about fuel filter, i may want to change it later. I dont know about O2 or vacuum leak. i dont get error code other than po365, also misfire

And i also checked exhaust camshaft sensor, it wasn't so hard to take out. I am getting one from

http://cgi.ebay.com/ebaymotors/ws/eB...m=120675610881

it's just 31.59 with o ring plus 8 dlls shipping, is this reliable one..??? price is not bad though...

I will post the result after i replace cps, I hope this is the main cause of poor mpg...

thx,
You're running rich. Are all the trips you take short ones? EDIT: also, are you feathering the throttle until the engine is warm?

Check O2 sensor, keep the tires pumped to correct pressure, make sure your brakes aren't sticking, etc. Also, if you modified anything it wouldn't hurt to disconnect the battery so the computer can readjust to your driving style and any new parts.

I average 8.5L/100km (34mpg) in combined city/highway driving with the 325i. This is according to the onboard computer, which I have reset twice just in case it was lying to me

Last edited by ac_2007; 04-25-2011 at 12:41 AM.
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Old 04-25-2011, 10:50 AM   #27
henryshih
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THANKS YOUR HINT ON BRAKES,

I DID NOTICED A BURNING SMELL ON THE WHEELS AFTER ROUTINE DRIVE FROM OMY WORK ABOUT 10 MILES OR LESS. I HAD REPLACED REAR BRAKE PAD RECENTLY AND IT MIGHT BE ONE OF THE CAUSES....

AC_2007,

What do you mean by " feathering the throttle until the engine is warm" ???

I am about to buy CPS from

http://cgi.ebay.com/ebaymotors/ws/eB...m=120675610881

Does anyone knows this auto parts ebayer ??? or any other recommendations.....

I am appreciated....

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Old 04-25-2011, 11:00 AM   #28
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Quote:
Originally Posted by henryshih View Post
THANKS YOUR HINT ON BRAKES,

I DID NOTICED A BURNING SMELL ON THE WHEELS AFTER ROUTINE DRIVE FROM OMY WORK ABOUT 10 MILES OR LESS. I HAD REPLACED REAR BRAKE PAD RECENTLY AND IT MIGHT BE ONE OF THE CAUSES....

AC_2007,

What do you mean by " feathering the throttle until the engine is warm" ???

I am about to buy CPS from

http://cgi.ebay.com/ebaymotors/ws/eB...m=120675610881

Does anyone knows this auto parts ebayer ??? or any other recommendations.....

I am appreciated....

My Honda winter car failed emissions because it had a sticking front caliper.. go figure

By feathering the throttle, I mean drive it gently and don't floor it, especially until the engine is warm.
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Old 04-25-2011, 11:11 AM   #29
henryshih
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Ok, i will double check the brakes this weekend, may get some lubs on....

Yes, i do drive slow even the engine is hot, i rarely rev over 3k rpm, so i think it's shouldn't be problem from my driving habit.....

Another question is, how to reset computer, so all error or records can be erased and i may drive a bran new car again... Is it possible...???
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Old 04-25-2011, 11:17 AM   #30
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Originally Posted by henryshih View Post
Ok, i will double check the brakes this weekend, may get some lubs on....

Yes, i do drive slow even the engine is hot, i rarely rev over 3k rpm, so i think it's shouldn't be problem from my driving habit.....

Another question is, how to reset computer, so all error or records can be erased and i may drive a bran new car again... Is it possible...???
Disconnect battery, I explained why in my previous post..
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Old 04-25-2011, 11:37 AM   #31
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Quote:
Originally Posted by reez777 View Post
I'm not sure if this will work for all E46 owners, but I increased my MPG from 20 to 25.5 by doing two things

i) taking the spare wheel out of the car.
ii) taking my girlfriend out of the car.

Weight Loss of the two items combined was enough to get my MPG shooting up.
Lol. I'm sure your woman was pleased.

All jokes aside; check the O2 sensors, they seem to be worn and are causing a loss of efficient consumption.

Good luck


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Old 04-25-2011, 11:53 AM   #32
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I was averaging 24 city/highway when I first purchased the car with 5000 miles. I worst I've seen my mileage was 17mpg average. Since replacing a few things my mileage increase to 22mpg.

Things replaced that improved my mileage:

K&N trashed and replaced with OEM filter
Iridiums trashed and replaced with OEM plugs
CCV
fuel filter
lightweight flywheel

I believe my Cats and O2 sensors may be somewhat fouled by the CCV failure, but I have significantly improved my mileage by replacing some aftermarket crap with OEM.
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Old 04-25-2011, 12:06 PM   #33
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My god how has nobody said this yet? REPOST. Search the forum, there's countless threads about this. In the end, driver determines mpg.
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Old 04-25-2011, 12:08 PM   #34
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Just went through thread going back 2 years and saw no mention of thermostat.

Check its function. If engine is running cooler than it wants to, it will burn a lot more gas. If it dips any at all below dead center on temp gauge, replace it. Not saying this to OP, since I doubt he's here, but to anyone reading.
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Old 04-25-2011, 07:45 PM   #35
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i like the idea about the thermostat... mine is stuck open it seems and it runs cool. I still average 26, but looking to replace it soon anyway.

XAVI - I agree about the iridiums, but I have ran many a k&n filters in my life and have one that I havent even installed yet. I am driving all week to make sure my MPG smooths out before installing it so I can determine the effect. Personally, I don't think the different air filter could have that big of an effect. Maybe I am missing something??

And REEZ - if you think ditching the girlfriend increases your MPG, you should see what ditching the WIFE does.
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Old 04-25-2011, 08:25 PM   #36
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I am driving all week to make sure my MPG smooths out before installing it so I can determine the effect. Personally, I don't think the different air filter could have that big of an effect. Maybe I am missing something??
You might be missing that IF the K&N flows more air, your ECM will inject more fuel to compensate and keep the Air/Fuel ratio the same and decrease your mileage......
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Old 04-25-2011, 08:36 PM   #37
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Originally Posted by dmax View Post
Just went through thread going back 2 years and saw no mention of thermostat.

Check its function. If engine is running cooler than it wants to, it will burn a lot more gas. If it dips any at all below dead center on temp gauge, replace it. Not saying this to OP, since I doubt he's here, but to anyone reading.
+1
my thermostat was stuck open and the car took a really long time to heat up, on my trip from LA to Vegas it couldn't get up to the middle...i still did get around 350+ miles on that tank of gas even by cruising at around 90 mph most of the way...
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Old 04-25-2011, 08:44 PM   #38
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I'm averaging 9.0 liters per 100km or 26mpg I'm pretty happy with that considering gas is up to $1.50 a liter for the good stuff

Edit: stupid autocorrect

Last edited by Dirty330i; 04-26-2011 at 04:33 PM.
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Old 04-25-2011, 09:00 PM   #39
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You might be missing that IF the K&N flows more air, your ECM will inject more fuel to compensate and keep the Air/Fuel ratio the same and decrease your mileage......

+1 I saw an increase .3 mpg since replacement two weeks. It seems to increase as the weeks go by.
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Old 04-25-2011, 09:14 PM   #40
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http://forum.e46fanatics.com/showthr...ht=improve+mpg

this will solve all your MPG problems! just putting it out there, search first then post
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