Engine Light On, 15mpg

[superdeadman]

hey all
i have a 99 528i auto, and i am not sure what's going on.
i got check engine light on, and after my friend hooked the car up to a computer, and we highly doubt that it's the oxygen sensor.

when the car runs, it smells bad, but the smell is different from the gas smell.

the mpg is poor. averages at about 15-16 mpg, but it's not a hummer or a ferrari, but a 2.8 liter 6 cylinder engine. What can cause that poor of a milage? i was reading a post, and someone with 540 said he was getting 24 mpg, and it's a v8 with 4.4 liters.

So if anybody have had the problem, or maybe knows what can cause it, please help!
thank you

[Torque]

Why do you doubt that it's the oxygen sensor ? Is that what the code scanner said ?

Other things to check: Spark plugs, air and fuel filter.

[TMac325is]

1) poor gas mileage very well could be caused by the oxygen sensor
2) bmws get poor mileage PERIOD
3) the guy with the 540 was probably lying unless he only drives on the highway, w/o stop lights
4) do what torque said
5) i have a 2.5L engine and i get 18-19 mpg

[Torque]

Originally posted by TMac325is@Apr 11 2005, 08:44 PM
1) poor gas mileage very well could be caused by the oxygen sensor
2) bmws get poor mileage PERIOD
3) the guy with the 540 was probably lying unless he only drives on the highway, w/o stop lights
4) do what torque said
5) i have a 2.5L engine and i get 18-19 mpg

[snapback]330354[/snapback]

You get 19 ? I'm lucky when I hit 18 with my heavy foot...

[Eric S.]

Originally posted by TMac325is@Apr 11 2005, 08:44 PM
1) poor gas mileage very well could be caused by the oxygen sensor
2) bmws get poor mileage PERIOD
3) the guy with the 540 was probably lying unless he only drives on the highway, w/o stop lights
4) do what torque said
5) i have a 2.5L engine and i get 18-19 mpg

[snapback]330354[/snapback]

Re 3) No lie here. I have a 1999 540/6. I have been gathering mpg data for literally months on my OBC's consum1 and it reads 24.0, occasionally dropping to 23.7. My daily commute is indeed mostly highway (12.5 miles out of 15.5), with only a couple of "stops" and one stoplight each way, but this mpg includes ALL driving I've done in the past 2 or 3 months (no "road trips" except as stated below).

Speaking of highway, a recent short 75-mile-each-way trip netted me 29mpg (consum2), including a lunch stop and a brief bit of testing at the BMW dealership (which was my destination). It had been over 30mpg, but the stops/starts cut the mpg.

Before you say my OBC must be off, I validated its accuracy right after I bought the car in October 2004, and it was consistently within about 1/2 mpg of my manual calcs.

The secret is: fresh plugs, filters, tire psi on the high end, and of course the ridiculously tall 6th gear, which allows only 1750rpm @ 60 mph. Oh, that and the fact that a clutch (and not fluid) connects my engine to its transmission...

These are the facts. This is why, at least for the 6-speed 540, I believe it is a myth that the I-6 gets significantly better mpg (altho there IS no engine smoother than the I-6).

So there ya go. Let the denials resume...

[superdeadman]

the spark plugs were replaced a month ago
i'm thinking about buying kn&n filter becuase i have read on the forum it's the absolute best, and the comp. did show that oxygen sensor was fine. When i drive, the real time gas consumption stays at 20 or above most of the time, esp. when i'm on hgwy, yet, i got 135mi/ 9 gal ... you do the math
the car does have 90k mi, so the fact is that i do need to replace oxygen sensor anyhow, but can it cause THAT bad of the gas milage? and what about the smell that is coming out of the car? it can't be gas leak because it doesn't smell like gas at all.

[Eric S.]

Originally posted by superdeadman@Apr 11 2005, 11:36 PM
the spark plugs were replaced a month ago
i'm thinking about buying kn&n filter becuase i have read on the forum it's the absolute best, and the comp. did show that oxygen sensor was fine. When i drive, the real time gas consumption stays at 20 or above most of the time, esp. when i'm on hgwy, yet, i got 135mi/ 9 gal ... you do the math
the car does have 90k mi, so the fact is that i do need to replace oxygen sensor anyhow, but can it cause THAT bad of the gas milage? and what about the smell that is coming out of the car? it can't be gas leak because it doesn't smell like gas at all.

[snapback]330513[/snapback]

1) Be careful with K&N (and other oil/cloth type air filters) - too much oil on the filter can play havoc with your MAF (at least that's true of the 540).
2) Have you checked/considered your cat(s)? I would think a bad catalyst could ruin your gas mileage and also possibly cause the rear/post-cat O2 sensors to give funny readings.
Just some more ideas. Wish I could help further.

[CosmosBlack]

On my 540i auto:
I get 17-19mpg in normal daily driving
and the best of 23mpg on long 400-mile highway trips

Eric, I'm not disputing you, but your claims are indeed hard to believe.
You must be really very light-footed and gentle...
Do you reset your consumption numbers for every test run?

[Eric S.]

Originally posted by CosmosBlack@Apr 12 2005, 03:51 AM
On my 540i auto:
I get 17-19mpg in normal daily driving
and the best of 23mpg on long 400-mile highway trips

Eric, I'm not disputing you, but your claims are indeed hard to believe.
You must be really very light-footed and gentle...
Do you reset your consumption numbers for every test run?

[snapback]330660[/snapback]

You just pointed out a key difference - the 5-cog auto versus the 6-cog manual. Keep in mind that in addition to the gear ratio, the manual's clutch allows less slippage realtive to a torque converter; the manual-equipped car weighs 55 fewer pounds as well. All that aside, I agree it is hard to believe that alone makes the difference.

As I already stated, I have not reset "consum1" for months, so in addition to my E-Z commute, it includes trips to the store, restaurants, gas station, my daughter's pre-school, etc. That's a LOT of data!

I assure you I have not pulled these numbers out of my a$$, nor do I drive like I have an egg under my foot. I don't abuse the car either though. I knew there would be denials.

This reminds me of dialogue I had in 2001-2002 with other Acura Legend owners who didn't believe me when I reported 28+mpg to them. 100% of the nay-sayers drove the ubiquitous automatic, whereas I had a rare 6-speed GS model (much rarer than 540/6's). That car also barely was above idle rpm at 60 mph.

I'd like to hear from others 540/6 owners to see how this compares. Maybe I am just lucky. I wish some of that "luck" would rub off on my hopelessly thirsty 13.5 mpg Expedition...

[superdeadman]

haven't thought about the cats at all...

my friend on a 6 spd 2002 maxima gets 22 mpg on average

cosmos - you get 17-19 avg with a 4.4l 8cyl... i got 2.8l 6cyl ,and i do worse than you... hehe

and i actually do believe eric. If you won't abuse the car too much and do use 6th gear alot, you may end up with a nice mpg reading. If you get 19, i bet he can get 22 or so because he can control when to shift and manuals are known to get better mpg.

would you guys recommend to put a whole air intake system, or just put a new air filter with stock intake. btw, will kn&n add some hp? because i read somewhere on the forum that a lot of aftermarket parts will reduce your hp instead of increasing them.

[CosmosBlack]

Eric, again, I am NOT disputing your claim.
Rather, I find it interesting and am very curious to know if your claims are indeed valid or accurate, as BMW doesn't even claim those high figures.

Note that if you do not reset your "Consump1"...it keeps records of previous long trips with recent short trips, all together, and put everything on an average. That's what I do too, I do not reset my "Consump1", but I do reset "Consump2" everytime I fill up, or go on a long trip, to get more accurate records for that particular period.

Do me a favor, this is what I do to counter check the OBC.
Everytime you fill up, reset the Consump2 to 0, and reset trip meter to 0.
The next time you fill up,
1. write down the mileage on the trip meter
2. write down the gallons needed to fill up

From there you get your own calculation of your actual consumption.
Of course this has to be logged for several fill ups and not just once, to be more consistent and accurate. This is what I do and I compare my own calculations to the OBC, the difference is usually minimal, like less than 1 mpg.

Please keep me updated!

[Jrf786]

I believe him. My 528 auto gets over 30mpg on the highway, but since I do most of my driving on the street and I have a heavy right foot, my average runs about 18mpg. So bearing in mind that he has a 6 speed manual, and I have 4 speed auto, I wouldnt doubt his claims.

[Eric S.]

Originally posted by CosmosBlack@Apr 12 2005, 03:43 PM
Eric, again, I am NOT disputing your claim.
Rather, I find it interesting and am very curious to know if your claims are indeed valid or accurate, as BMW doesn't even claim those high figures.

Note that if you do not reset your "Consump1"...it keeps records of previous long trips with recent short trips, all together, and put everything on an average. That's what I do too, I do not reset my "Consump1", but I do reset "Consump2" everytime I fill up, or go on a long trip, to get more accurate records for that particular period.

Do me a favor, this is what I do to counter check the OBC.
Everytime you fill up, reset the Consump2 to 0, and reset trip meter to 0.
The next time you fill up,
1. write down the mileage on the trip meter
2. write down the gallons needed to fill up

From there you get your own calculation of your actual consumption.
Of course this has to be logged for several fill ups and not just once, to be more consistent and accurate. This is what I do and I compare my own calculations to the OBC, the difference is usually minimal, like less than 1 mpg.

Please keep me updated!

[snapback]330928[/snapback]

Hey Cosmos -
You make two very good points, but I already addressed them in the above ramblings:
1) I have not been on any road trips other than the daily grind over the past couple of months since I reset my consum1 (we load the fam into my wife's Expedition for such outings). Except for my 75-mile-each way trip last Saturday, for which I reset consum2 to measure (and got 29 at the end). To illustrate how many miles I accumlated on consum1, that very trip increased my consum1 by only 0.2 mpg to 24.2 (it's back down to 24.0 now).
2) I did many manual validations of consum1 and consum2 for the first month after I bought the car (October 2004), using exactly the technique you suggested. I even averaged total miles across multiple tankfuls (to mitigate refill technique variation). As mentioned, there was barely 0.5mpg difference compared to consum1 & 2. Unless my range drastically changes, I see no need to revalidate now.

On that note, I regularly go over 400 miles between fill-ups. Anyone else with a 1999 or newer 540/6 who doesn't weekly autocross care to share mpg? It would also be interesting to compare the 1999+ M62TU to the 1997-98 M62-engined 540's as well. Every statistician's dilemma - we need data!!!

PS - Cosmos, your 540 looks very mean, in a good way. It's tough to beat the all-black look; nice...

[CosmosBlack]

Eric,
I guess I'd have to take your word for the claim! Also based on your post history, you seem to know what you're talking about.
And yes, I'd love to hear from other 6spd 540i's. I personally have owned 2 540 autos, but never a stick.

Oh, and thanks for the compliment on my car!

[billB]

Guys what about the manufacturers data on MPG? I never seen it reach the 30 MPG mark not even on I6s.....although the wealth of data collected depends upon variations of different driving condition; i.e. lab controlled studies (ideal conditions) to come up with a good MPG/ positive results for marketing...don't you think if a 540 can do close to 30 MPG it will be a good place to start a TV ad?

If this is the case then BMW should use this info. to compete with other manufacturers; don't you think?