sudden drop in fuel economy

longliven54 · 11-23-2013, 03:50 PM

i have a 07 335i A/T that i have owned for past 4 years. i am FBO, and have always averaged 600kms+( 370miles) per tank for ever. my driving habits are same, route to work is the same yet i am experiencing a sudden drop in fuel economy.
lately i have been getting only 350-400kms(240miles)

mileage: 112k kms
spark plugs/oil changed less than 2000kms ago
i have inspected the spark plugs and none have gas on them that could suggest a leaky injector.
shell 91 gas from same station
no codes on jb4

it has been constant rain for the past month, and i have not been running my car as hard as i normally do. granny shifting keeping RPM under 3000.

it probably is un-related, but i have been getting low battery symbol occasionally. would that cause fuel economy to drop from poor ignition.

can anyone shed any light on this matter? is there some checks that i could do?

Brule · 11-23-2013, 06:31 PM

One JB4 iso testing firmware (25 c i think) got me around 400km a tank.

Then the proper released firmware I got back up around 500km a tank.

When using BMS back end pump flash, consumption was shown in dash from 12L/100km (JB4 only) - 14L/100km(BMS flash)

longliven54 · 11-23-2013, 06:55 PM

Quote:

Originally Posted by Brule

One JB4 iso testing firmware (25 c i think) got me around 400km a tank.

Then the proper released firmware I got back up around 500km a tank.

When using BMS back end pump flash, consumption was shown in dash from 12L/100km (JB4 only) - 14L/100km(BMS flash)

hmmm. am on the same firmware for the last 7-8 months now. in dash says 11.1L/100kms

longliven54 · 11-23-2013, 06:55 PM

Quote:

Originally Posted by Brule

One JB4 iso testing firmware (25 c i think) got me around 400km a tank.

Then the proper released firmware I got back up around 500km a tank.

When using BMS back end pump flash, consumption was shown in dash from 12L/100km (JB4 only) - 14L/100km(BMS flash)

hmmm. am on the same firmware for the last 7-8 months now. in dash says 11.1L/100kms

Killerfish2012 · 11-23-2013, 08:11 PM

Any codes for a failed thermostat?

SgtGoldy · 11-23-2013, 08:19 PM

subbed because I'm at that gas mileage lol

CoralRed335XI · 11-23-2013, 08:23 PM

Winter-blend gas?

longliven54 · 11-23-2013, 08:53 PM

Quote:

Originally Posted by Killerfish2012

Any codes for a failed thermostat?

nope, no codes. checked via BT cable as well. auto clear is turned off on JB4.

longliven54 · 11-23-2013, 08:58 PM

Quote:

Originally Posted by CoralRed335XI

Winter-blend gas?

no e85 here in canada. just regular 91 oct. there is no winter blend, it doesnt get cold where i live. its just constant rain from pretty much oct-march.

nothing is really pointing to any certain thing, but such a significant drop in fuel economy usually means something is not working as how it should.
i get better fuel economy than this while i am having all-out fun on the mountain roads boosting 14+psi

longliven54 · 11-23-2013, 09:00 PM

Quote:

Originally Posted by SgtGoldy

subbed because I'm at that gas mileage lol

have you just started getting poor mileage, or has it been the same? have you checked out your injector/spark plugs for gas-fouling yet?

Killerfish2012 · 11-24-2013, 01:57 AM

Quote:

Originally Posted by longliven54

nope, no codes. checked via BT cable as well. auto clear is turned off on JB4.

When was the last time you changed your rear diff fluid? If it's been a while change 100% or as much as you can of it, to royal purple rear diff fluid for a nice increase in gas mileage.

longliven54 · 11-24-2013, 02:04 AM

Quote:

Originally Posted by Killerfish2012

Quote:

Originally Posted by longliven54

nope, no codes. checked via BT cable as well. auto clear is turned off on JB4.

When was the last time you changed your rear diff fluid? If it's been a while change 100% or as much as you can of it, to royal purple rear diff fluid for a nice increase in gas mileage.

k. am gonna give that a try. still don't think its this that's causing this drop in economy

longliven54 · 11-28-2013, 09:25 PM

bump. my car finally popped a code for LPFP. i see there are many upgrades for people who get to run e85, whats the best upgrade for a car that will never see e85?
i am guessing that LPFP has been behind my recent poor fuel economy. any help in selection will be highly appreciated.

pwilde · 11-30-2013, 09:37 AM

The differential fluid change may assist gas mileage but it's not what is wrong with the vehicle. Mileage doesn't drop that drastic without massive fuel consumption somewhere. To really fix it you need to search for the location of abnormal consumption and I would recommend holding off on the fluid swap to maintain your base line mileage and current mileage without adding another variable.

pwilde · 11-30-2013, 10:02 AM

Do you have a rough idle that could suggest a miss fire due to a possible fouling of plug or bad ign. coil? This doesn't always produce a check engine light and can be pretty taxing on fuel economy. Also I would see if it continues over one tank of fuel as even the same gas station can get a ad batch of fuel.

TT-Tom · 11-30-2013, 10:15 AM

Quote:

Originally Posted by longliven54

bump. my car finally popped a code for LPFP. i see there are many upgrades for people who get to run e85, whats the best upgrade for a car that will never see e85?
i am guessing that LPFP has been behind my recent poor fuel economy. any help in selection will be highly appreciated.

The factory setup is the only reliable solution that I know of at this point. Many people have upgraded their lpfp only to have issue after issue. No need to upgrade yours just replace it. Also rain will drop your economy massively due to the higher rolling resistance and the humidity doesn't help either.

longliven54 · 11-30-2013, 02:04 PM

Quote:

Originally Posted by pwilde

Do you have a rough idle that could suggest a miss fire due to a possible fouling of plug or bad ign. coil? This doesn't always produce a check engine light and can be pretty taxing on fuel economy. Also I would see if it continues over one tank of fuel as even the same gas station can get a ad batch of fuel.

no rough idle. have checked for fouling on spark plugs.
low batt sign and lpfp code are the only 2 symptoms.

longliven54 · 11-30-2013, 02:12 PM

Quote:

Originally Posted by TT-Tom

Quote:

Originally Posted by longliven54

bump. my car finally popped a code for LPFP. i see there are many upgrades for people who get to run e85, whats the best upgrade for a car that will never see e85?
i am guessing that LPFP has been behind my recent poor fuel economy. any help in selection will be highly appreciated.

The factory setup is the only reliable solution that I know of at this point. Many people have upgraded their lpfp only to have issue after issue. No need to upgrade yours just replace it. Also rain will drop your economy massively due to the higher rolling resistance and the humidity doesn't help either.

where I live , it rains 250+ days/ year. all through this I maintained 600(kms/tank. its just been last 1 month that I have been noticing this drop.

I use 19" tires(235 f, 255 r) for summers, and 17"(225 square) for the rain/winter time. I usually see a little increase in fuel economy when I move down to 17".

thanks for the advice to stick with OEM lpfp.

11-23-2013, 03:50 PM	#1
longliven54 Lieutenant 14 Rep 455 Posts Drives: 2007 335i e90 auto Join Date: Jan 2011 Location: victoria iTrader: (6)	sudden drop in fuel economy i have a 07 335i A/T that i have owned for past 4 years. i am FBO, and have always averaged 600kms+( 370miles) per tank for ever. my driving habits are same, route to work is the same yet i am experiencing a sudden drop in fuel economy. lately i have been getting only 350-400kms(240miles) mileage: 112k kms spark plugs/oil changed less than 2000kms ago i have inspected the spark plugs and none have gas on them that could suggest a leaky injector. shell 91 gas from same station no codes on jb4 it has been constant rain for the past month, and i have not been running my car as hard as i normally do. granny shifting keeping RPM under 3000. it probably is un-related, but i have been getting low battery symbol occasionally. would that cause fuel economy to drop from poor ignition. can anyone shed any light on this matter? is there some checks that i could do? __________________ JB4 G5 / VRSF IC / STETT CAI / GREDDY / custom exhaust / iRotora cross drilled rotots / snow stage 3 meth / 19" iForged senekas / upgraded speakers n CF woofer box / M3 bits/ DINAN camber plates/ KONI/ megan racing toe arm/ supreme power lowering perch
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11-23-2013, 06:31 PM	#2
Brule Brigadier General 841 Rep 3,190 Posts Drives: 2007 335i e92 6spd man Join Date: Jul 2013 Location: Darwin iTrader: (0)	One JB4 iso testing firmware (25 c i think) got me around 400km a tank. Then the proper released firmware I got back up around 500km a tank. When using BMS back end pump flash, consumption was shown in dash from 12L/100km (JB4 only) - 14L/100km(BMS flash)
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11-23-2013, 08:11 PM	#5
Killerfish2012 Colonel 181 Rep 2,301 Posts Drives: E90 335I, E92 M3 Join Date: Feb 2012 Location: Midwest iTrader: (9)	Any codes for a failed thermostat? __________________ '07 335I w/ Mods '13 X1 Stock '11 X3 K&N
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11-23-2013, 08:19 PM	#6
SgtGoldy SuperFastYo 51 Rep 790 Posts Drives: N54 335i TiAg Join Date: Nov 2013 Location: Orange County, CA iTrader: (3)	subbed because I'm at that gas mileage lol __________________ C63 AMG - LSD - Straight Pipe - EuroCharge v5 - Vossen CV7 -
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11-23-2013, 08:23 PM	#7
CoralRed335XI Captain 103 Rep 646 Posts Drives: 2008 E92 335XI Coupe Join Date: Aug 2011 Location: NJ,VA iTrader: (4) Garage List 2008 BMW 335XI [3.66]	Winter-blend gas? __________________ 2008 E92 335XI, Space Gray on Coral/Fox Red Hybrid M3 seats, Premium, Cold Weather, Comfort Access, iPod. Mods: Fox Red M3 seats up front, KW V1, ER CP + TIAL BOV.
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11-28-2013, 09:25 PM	#13
longliven54 Lieutenant 14 Rep 455 Posts Drives: 2007 335i e90 auto Join Date: Jan 2011 Location: victoria iTrader: (6)	bump. my car finally popped a code for LPFP. i see there are many upgrades for people who get to run e85, whats the best upgrade for a car that will never see e85? i am guessing that LPFP has been behind my recent poor fuel economy. any help in selection will be highly appreciated. __________________ JB4 G5 / VRSF IC / STETT CAI / GREDDY / custom exhaust / iRotora cross drilled rotots / snow stage 3 meth / 19" iForged senekas / upgraded speakers n CF woofer box / M3 bits/ DINAN camber plates/ KONI/ megan racing toe arm/ supreme power lowering perch
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11-30-2013, 09:37 AM	#14
pwilde Private First Class 21 Rep 147 Posts Drives: 2008 335i 6spd Join Date: Jan 2012 Location: Madison, WI iTrader: (0) Garage List 2008 BMW [0.00]	The differential fluid change may assist gas mileage but it's not what is wrong with the vehicle. Mileage doesn't drop that drastic without massive fuel consumption somewhere. To really fix it you need to search for the location of abnormal consumption and I would recommend holding off on the fluid swap to maintain your base line mileage and current mileage without adding another variable.
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11-30-2013, 10:02 AM	#15
pwilde Private First Class 21 Rep 147 Posts Drives: 2008 335i 6spd Join Date: Jan 2012 Location: Madison, WI iTrader: (0) Garage List 2008 BMW [0.00]	Do you have a rough idle that could suggest a miss fire due to a possible fouling of plug or bad ign. coil? This doesn't always produce a check engine light and can be pretty taxing on fuel economy. Also I would see if it continues over one tank of fuel as even the same gas station can get a ad batch of fuel.
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