low gas mileage: change coils and sparks w/out any code being thrown

simexous · 05-30-2015, 05:42 AM

Hi

I get very low mileage on my 2005 EU 330i w/ conservative city driving. I am thinking about changing coils and spark plugs, but my car mechanic is saying we don't really need to b/c they're not throwing any codes.

Do I take his word for it, or have him change them anyways? How about my MAF sensor? been noticing a rough idle lately, but again no codes.

I am currently getting about 12.5mpg (US mpg) in the city.

Thanks,

Phil325i · 05-30-2015, 08:48 AM

I'd agree with your mechanic about not changing the coils, but a change of plugs is often worthwhile. And have you checked your air filter? A clogged filter will devastate gas mileage...

queensfield · 05-31-2015, 01:49 PM

Low mileage typically implies improper air-fuel mix and ignition. Check your oxygen sensors, especially the two that are upstream of the catalyst

jon_335 · 05-31-2015, 07:58 PM

The way I understand it is that coils are either good or bad … there is no in between. So as long as you're not throwing codes, don't mess with the coils.

Definitely check your air filter. And before considering replacing your MAF, give it a good cleaning.

BashShah · 06-08-2015, 03:01 AM

How many k do you have?
That would be my first indication on whether to change the plugs and coils or not.
80 to 100k.....change em.

DN

floydarogers · 06-08-2015, 10:17 AM

Quote:

Originally Posted by Phil325i

I'd agree with your mechanic about not changing the coils, but a change of plugs is often worthwhile. And have you checked your air filter? A clogged filter will devastate gas mileage...

+ Changing coils that haven't failed (and thrown misfire codes) is a waste of money.

05-30-2015, 05:42 AM	#1
simexous New Member 3 Rep 15 Posts Drives: pre-LCI e90 330i (258 bhp) Join Date: Jul 2012 Location: Casablanca iTrader: (0)	low gas mileage: change coils and sparks w/out any code being thrown Hi I get very low mileage on my 2005 EU 330i w/ conservative city driving. I am thinking about changing coils and spark plugs, but my car mechanic is saying we don't really need to b/c they're not throwing any codes. Do I take his word for it, or have him change them anyways? How about my MAF sensor? been noticing a rough idle lately, but again no codes. I am currently getting about 12.5mpg (US mpg) in the city. Thanks, Last edited by simexous; 05-30-2015 at 12:10 PM.. Reason: clarification
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05-30-2015, 08:48 AM	#2
Phil325i Brigadier General 616 Rep 3,194 Posts Drives: E92 325i MSport Coupe Join Date: Apr 2012 Location: UK South East iTrader: (1) Garage List 2009 BMW 325i Coupe [6.00]	I'd agree with your mechanic about not changing the coils, but a change of plugs is often worthwhile. And have you checked your air filter? A clogged filter will devastate gas mileage... __________________ E92 pre-LCI 325i - Ohlins R&T; H&R spacers; M3 strut brace; Swift thrust sheets; 3 x chassis braces; diff brace; N53 V-brace; 034 subframe inserts; BMS clutch stop; BMS CDV; RE g/box mounts; Delrin shift bushes; Saikoumichi OCC; Cyba scoops; BMW Perf Exhaust; HEL s/steel brake hoses; M3 rear spoiler; Recaro Sportster CSs; M3 white dash LEDs; LED Angels; LED side repeaters; BMW Perf black grille; CSL reps; SSDD carbon diffuser; Monster Wrap black roof/clear front
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05-31-2015, 01:49 PM	#3
queensfield First Lieutenant 21 Rep 364 Posts Drives: 2006 330i E90 Join Date: Aug 2011 Location: So Cal iTrader: (0)	Low mileage typically implies improper air-fuel mix and ignition. Check your oxygen sensors, especially the two that are upstream of the catalyst
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05-31-2015, 07:58 PM	#4
jon_335 Second Lieutenant 15 Rep 276 Posts Drives: 2007 BMW 335i Join Date: Feb 2013 Location: North Carolina iTrader: (1)	The way I understand it is that coils are either good or bad … there is no in between. So as long as you're not throwing codes, don't mess with the coils. Definitely check your air filter. And before considering replacing your MAF, give it a good cleaning. __________________ 2007 BMW 335i \| Garner, North Carolina
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06-08-2015, 03:01 AM	#5
BashShah Colonel 296 Rep 2,015 Posts Drives: 2012 335i Sedan Join Date: Oct 2012 Location: Vancouver, Canada iTrader: (0)	How many k do you have? That would be my first indication on whether to change the plugs and coils or not. 80 to 100k.....change em. DN
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