Need some mpg improvement ideas

I posted this on Roadfly, but there isn't much traffic there, so here it is:

My car runs beautiful, however, the mpg is creeping up steady, and I ran out of ideas. The mpg is city driving related. i haven't been on a highway in a long time.



Up until about 4 years ago, the mpg was around 10.8 - 11.2 l/100Km (21.7 - 21 mpg). Then, it started to go up ever so slightly. Today I am at around 13.2 l/100km (17.8 mpg), and the trend is still going up. I will post a list with engine related stuff I did on my car, maybe this will help:

• ATF was changed together with filter in fall/winter 2007/08 (55k / 88600Km)
• Winterized CCV 2008 -feb
• New pre-cat O2 sensors (Bosch) - Oct 2008 (66k / 106000 Km)
• Beisan vanos seals Aug 2009 (74 k / 120000 Km)
• New fuel filter Sep 2009 (75k / 120000 Km)
• Cooling overhaul (incl belts, pullies, hoses, etc) & new DISA May 2011 (89k / 143000 Km)
• New injectors (OEM) Sep 2011 (91k / 147000 Km)
• Cleaned TB & ICV. New MAF (OEM), new sparkplugs (NGK), new VCG, replaced all vacuum hoses (Jul 2012) (99k / 159000 Km)

Other maintenance was also done, like oil changes, coolant flush, brake fluid flush, etc and various engine not related maintenance. But this mpg up-creep is just puzzling. My driving habits or route did not change, and I use the same Shell V-power gas since I purchased the car in '06 (with the odd different brand fuel once a year or so).
What did I overlook? I think I will change the post-cat O2 sensors as well regardless of "monitoring" status only. But I am not sure this will change the status-quo.

Consider gas quality slipping 30%?

Doru, we're in the same boat. My 525i averages 18.5mpg. I'd like to know too.

Um, I have a 96k 530i 5spd manual and am averaging 29-30.5 MPG on the highway. I've been driving it from Tampa to Pensacola and back every week since I got the car almost a month ago. I've been averaging anywhere from 27-30.5mpg on the highway. 22-26 MPG around town. Thats on 87 and 89 fuel with some crazy driving. On 89, doing 80 I pull 29.0. with 87 I get 27.5. Manual trans oil is original, on my list to replace soon. O2's are original and the fuel filter is original. I did cooling system, plugs, tires, alignment and diff lube when I got the car 3 or 4 weeks ago with 93k. My recommendation would be to change out the diff oil with 75/90 Mobil 1 or another 75/90 Syn GL-5 Gear oil of your choice. Our cars are open diff, special oil is not required. When I did my diff oil the original stuff was toast. Let me repeat that, TOAST. And for some reason a lot of manufactures and people like to run the 75/140. News flash. We have 225 HP. 75/90 synthetic is more than adequate and more MPG friendly. 75/140 is more warranty friendly for reduced idiot failures.

On a side note, my car revs too dang high on the highway. It needs a 6th gear. 3,150 rpm @ 80 is a joke. 2,500 or 2,750 would be ideal for just cruising.


EDIT: for reference my 335i is getting about 27-29 on the highway. Low 20-24 around town. All on 93 gas. SO my 530i is older, bigger, heavier and more fuel efficient. But i's missing two turbos and has skinnier rear tires.

I notices ATF and filter change gets some improvement on the mpg, I had the ATF changed last week, I was around 13.7-14.2l/100km, I got down to the lowest point of 12.6km/100km on the same road to and from work.

Hi D...!

I HIGHLY suspect the CCV...
Speaking from experience...

IMO, the sooner the CCV is DELETED/ or replaced with a better option, the better...

Thanks!
Jason

Originally Posted by Jason5driver

Hi D...!

I HIGHLY suspect the CCV...
Speaking from experience...

IMO, the sooner the CCV is DELETED/ or replaced with a better option, the better...

Thanks!
Jason

But i had good gas mileage with the old CCV & new CCV. Then it started to slip away. the mpg readings are consistent with the lower range I get. I'm at 450 Km (280 miles) between fill-ups now.... No smoking, no white vapors nothing. Tailpipe is clean as it gets, but looks like somehow I burn more fuel?

P.S.: this summer, after I cleaned the TB & ICV, changed the sparkplugs & vacuum hoses, the mpg improved suddenly. Lasted only about a week, then it slipped abruptly (from the "normal" 10.8 - 11.2 l/100km to 13.2 l/100 Km). I am stumped.

Changing the post-cat sensors won't help fuel use.

Have you considered that the tires may be causing more drag as they wear down? Also, changes in wheel alignment can cause drag, too.

This is an outside shot, but the cats may be slowly clogging up, and increasing back pressure.

Originally Posted by edjack

Changing the post-cat sensors won't help fuel use.

Have you considered that the tires may be causing more drag as they wear down? Also, changes in wheel alignment can cause drag, too.

This is an outside shot, but the cats may be slowly clogging up, and increasing back pressure.

the tires are new (changed them this spring). Alignment was done as well around that time.

Should I try this:

Partially Clogged injectors? Increase in Ethanol in the fuel is probably not good for the injectors and might clogged them up a bit.

I'm sorry I can't help but laugh at y'all complaining about get 18mpg city. My 540i gets 14 on a good day in Charlotte and 12 in Boone. I suspect fuel filter on my end, but I'm busy with the valley pan right now so it will have to wait. I did put a bottle of techron in and noticed 2-3 mpg improvement in city and highway for about 5k miles. Your fuel filter is like 3 years old it may be worth changing, and give the techron a go.

Originally Posted by mbell666

Partially Clogged injectors? Increase in Ethanol in the fuel is probably not good for the injectors and might clogged them up a bit.

I don't think V-power (Shell) has ethanol. Injectors are brand new.

Have you checked your brakes for a more than ordinary drag. That should include your e-brake. Jack up each wheel and give it a spin. And a bottle of Techron can never hurt. Just guessing!

go on a diet!

But seriously, have you changed your air filter lately?

problem with most cars is Air pressure in your tires, simple and basic. But, I read a survey where 9 out of 10 cars on the road had wrong pressure in the tires. Now it may not seem like much, but it could very easily impact your MPG. Also things like wheel bearings, alignment, extra weight in your trunk or car, engine splash shield removed, Any excessive electrical draw, like amps subs etc...causing your alt to work harder and require more input from the engine, maf recently cleaned?

You've addressed some big stuff...how bout some of the basic stuff. Also check for the brake drag and warped rotors, anything that adds to rolling resistance will add to increase load on the engine.

Also are your tires 'stock' you haven't added width to the tires ...that too will cut into mileage...GL

Originally Posted by 16valex

go on a diet!

But seriously, have you changed your air filter lately?

The air filter is OK, but I will change it for *****z & giggles

Originally Posted by GSXRYDER

problem with most cars is Air pressure in your tires, simple and basic. But, I read a survey where 9 out of 10 cars on the road had wrong pressure in the tires. Now it may not seem like much, but it could very easily impact your MPG. Also things like wheel bearings, alignment, extra weight in your trunk or car, engine splash shield removed, Any excessive electrical draw, like amps subs etc...causing your alt to work harder and require more input from the engine, maf recently cleaned?

You've addressed some big stuff...how bout some of the basic stuff. Also check for the brake drag and warped rotors, anything that adds to rolling resistance will add to increase load on the engine.

Also are your tires 'stock' you haven't added width to the tires ...that too will cut into mileage...GL

I always check tire pressure. Rubber size is OEM ///M-sport (235x40x18 & 265x35x18).
My trunk is empty, and usually it's only me driving the car - it's my DD. Brake drag was adressed this year - I changed all the brake rubber boots, the brakes are fairly new, fluid changed every 1 1/2 - 2 years. MAF is brand new (the old one was still good, but I changed it anyways). The new amp is not installed yet.
The only thing I haven't changed from your list are the bearings, but there's no noise. I had the car on jacks last week, and both front wheels turn freely, very nice. No noise. Can't check the rears (for free spinning), but there's no noise either.

P.S.: no spalsh shield removed.

Get a obd2 scan tool or DIS and look at your fuel trims. Don't guess and throw parts and money at the problem.

Doru
Here is an answer on your question
"i haven't been on a highway in a long time"

If you drive M54 in city all time MPG will go down
Take a long trip on a HW 200+km with seafoam in tank
This will clean engine oil sludge so your MPG will be better
Keep tire pressure 37PSI HW 35PSI City

Another healthy staff for our engine is an autoRX
http://www.auto-rx.com/

give it a try, talking from experience , you will be happy with result

GL

Originally Posted by Max_VQ

Get an OBD2 scan tool or DIS and look at your fuel trims.
Don't guess and throw parts and money at the problem.

+1...!
Great Post...!

Thanks!

Originally Posted by doru

But I had good gas mileage with the old CCV & new CCV.
Then it started to slip away.
The mpg readings are consistent with the lower range I get.
I'm at 450 Km (280 miles) between fill-ups now....
No smoking, no white vapors nothing.
Tailpipe is clean as it gets, but looks like somehow I burn more fuel?

P.S.:
This summer, after I cleaned the TB & ICV, changed the spark plugs & vacuum hoses, the mpg improved suddenly.

Lasted only about a week, then it slipped abruptly (from the "normal" 10.8 - 11.2 l/100km to 13.2 l/100 Km).
I am stumped.

Hey D...!
Yes, I have done similar to what you have done...
Replaced the CCV, cleaned the ICV, and throttle body, replace the rubber Intake Elbow, and various vacuum hoses...
Yet, the new CCV seemed to deteriorate faster than normal...
Very weird IMO, to say the least... LOL!
Lately, I have noticed more fuel fumes at start-up...

I am thinking/ GUESSING it has to do with:
1. The Secondary Air Pump,
2. Air Pump Valve that feed into the Secondary Air Pump, and
3. The Disa Valve, specifically with the deteriorated rubber frame-work around the Flapper Assembly...

I suspect a LOT of Carbon Build-Up in these areas causing the majority of the problems...

Best of LUCK...!
Let me know if I can help...!

Thanks!
Jason

I am not sure you are right about Shell V Power and ethanol. I use it here in NJ and I am pretty sure it has ethanol. Fuel consumption will change with ethanol because it has lower energy content for a given volume. I believe the percentage of ethanol in our fuel has been creeping up that last few years but I have no hard data to back that up. I do remember reading that oil companies also do things for winter blends that tend to increase fuel consumption in this region of the USA. I have noticed in my 530i that with multiple short trips at low speeds (local driving), my mileage is 16-18 mpg. As soon as I mix in some highway or steady state 50 mph driving on two lane country roads, my mileage increases to 22-23 mpg average range. Pure highway driving is in the high 20's. Our cars do not do well with stop and go driving. I am sure it is down to their weight and how much energy it takes to accelerate from a stand still.

Check back on all the spots vacuum leaks can occur--you know them as well as I. Back behind the intake and of course the Disa valve--I make my own gasket to fit between it and the intake just to make sure there's no problem there. As your stating your watching the mileage decrease--where you live can also be a factor in this--it's getting cold again and as it gets colder , it's taking more time for the engine to heat up to were it needs to be for effiency. Check those fuel perimeters athat might give you a start--I recently change out my oil temp sensor and helped my car with extra mileage--but there was a code thrown in that instance--might take some electrical cleaner and clean all of the hot plugs that is associated with the fuel delivery--I changed out my per 02 sensors back over a month ago and used the Denso brand this time--my average fuel useage went from 23.7 to 25.8--on the highway it's at 31 to 32--I would also suggest that you take the car out for a long drive from time to time just to blow the soot out of it--and cheak what kind of mileage your getting out on say 100 mile drive--it's falll get out and see some country--lets hear back on what you find

^ I have to disagree with the above Auto-RX advise. Use a good synthetic oil; M1 or BMW etc and change it more often if you need to. OR, do a engine flush/Seafoam before dumping your oil.

Bump up d tyre pressure 2psi all around and see.i get 29mpg per obc

Sent from my GT-I9070 using Bimmer App

Originally Posted by moots

Bump up d tyre pressure 2psi all around and see.i get 29mpg per obc

...but your fuelly stats says differently
10.7L/100k, or 22mpg...and that's @ 10% city use????

Gas mileage is such an illusive thing, with so many variables effecting it that for me it is often impossible to account for differences. However, my car gets pretty consistant around town mileage, 19 to 20 mpg. Recently I discovered a station in town that sells pure premium i.e. no ethanol and started to use it. It appears from a fairly small time sample that my mileage has jumped to 21.5 with that being the only change.