How does the BMW E39 adapt to high altitudes when you go from sea level to 6000 feet?

This thread today, where a user went from a low altitude warm area to a high altitude cold area, got me wondering how the E39 adapts to altitude when it comes to engine control adjustments:

Originally Posted by kross1300

I recently moved from San Diego to Breckenridge, CO and I have been having some trouble with how my car runs!

I've noticed in the past when I drove from San Jose (about 100' ASL) to Tahoe (around 6,000' ASL), my car used to stumble more so than I thought it should (but I've since replaced all the hoses due to a vacuum leak in the throttle boot and CCV lower vent hose and air pump vent hose).

To better understand how the bimmer adapts to altitude, I ask the general question:
Q: What does our E39 do differently at altitude than at sea level?

In a nut shell, thats what your O2 sensors and MAF sensors are for. They are constantly measuring the air intake and sniffing the exhaust mixture for the proper fuel air ratio which will properly compensate for temperature and pressure. In the old days with carburetors, if you were going on a trip to the mountains, you would turn the mixture screws in a half turn to lean the carbs out a bit. Then undo do it when you got back.

Bee-when warm, any car is in closed loop mode so the maf is measuring air passing maf and sending an anticipated fuel injector spray duration period to the ECU. Then, the pre-cat O2 sensor has the final word and determines how well the ECU did based upon Maf signal. The leaner air at higher altitudes will tell the O2 that car is running rich cause there isn't enough air to support your adaptation values for normal operation. ECU will start to change the adaptation values to take fuel injector pulse duration down to make the O2 sensor happier with less gas to match the lessor air. The car does not know how long you are going to be in the higher altitude, so it may not make a full adaptation for the height above sea level in one trip. If you moved to higher altitude permanently, it would change your whole table and then your car would run lean at sea level until adaptation values got used to being at sea level and getting more air and lengthen the fuel injector pulse time. Make sense?

Normally aspirated cars lose power at altitude because the air is thinner. Turbos make up a huge difference the higher up you go.

Originally Posted by Kamdog

Normally aspirated cars lose power at altitude because the air is thinner. Turbos make up a huge difference the higher up you go.

Does your BMW have a turbo? How does this remotely answer the question?

Originally Posted by 540iman

Does your BMW have a turbo? How does this remotely answer the question?

His though process is correct and I'm sure he did not know that the ECU would compensate thereby suggesting the use of a turbo which will increase atmospheric pressure. The decrease in atmospheric pressure between SD and CO can and will be compensated overtime via the ECU.

At least he was contributing and not being a jerk off! What did you contribute to this thread? Absolutely nothing. FYI: No matter where you go in our atmosphere the gas mixture is the same... Depending on your altitude only the PRESSURE will change.

Maybe you should spend some time in college instead of the auto garage? Just Saying you might want to give it a thought.

Originally Posted by 540iman

Can I ask you something kinda personal? When BMW Mtech'd your rear....well, did it hurt? :

This is just immature. Grow up!

Your statements are just not true, but it's not worth arguing with you. Oh, btw...I got my MBA in 2007 at age 53. When did you get yours?

Originally Posted by 540iman

Does your BMW have a turbo? How does this remotely answer the question?

he's just making a general point... the OP asked how does altitude affect motors, he's saying turbo cars do better at altitude than N/A cars, which is true.... don't hate

This information, added today, is apropos to this thread:

Originally Posted by rdl

I think EDJACK and FUDMAN have it right regards engine performance. Engine sensors, particularly the MAF (mass air flow) and O2 sensors, compensate for changes in atmospheric parameters. FWIW, carbureted engines were/are an entirely different matter - 5,000 of altitude would definitely require re-jetting to maintain best performance. And depending on engine and carb, best at altitude may be a far cry from sea level.

Temperature ranges are primarily an oil issue, i.e. is the oil in the engine suited to the ambient? If you use BMW LL-01 certified oil you will be fine. The owners manual says approved oils in 5W-40 or 5W-30 viscosities "may be used for driving in all ambient temperatures."
If you are in below freezing temps for a prolonged period beware of potential CCV problems. Check Best Links for the story. Bottom line: avoid a steady diet of short trips that can build up sludge in the CCV or install the cold weather version of the CCV.
My 2003 530 takes ~10 minutes driving (not idling) to reach normal coolant temp in -25C, -13F. I've no indication of engine problems using LL-01 synthetic.

Maximum power depends on the mass of air that can be drawn into the cylinders. At 5,000 ft air density is ~83% of sea level. So maximum power would be about 83% of sea level. This corresponds pretty well with the rule of thumb that max power is reduced 3% for every 1,000 of altitude on normally asperated engines, which ours are. So, WOT throttle acceleration will be a little less than at sea level.

Highway gas mileage should improve. Aerodynamic drag accounts for ~80% of the power requirement at highway speeds. Drag is proportional to density. So a 15% reduction in density should result in a noticeable improvement in MPG. City driving MPG is primarily a function of tire rolling resistance and energy wasted on stops. Neither of these vary with altitude; city MPG should be the same as sea level.

Note though, as discussed in other threads, MPG depends on so many factors that any change compared to your current driving patterns and routes may be difficult to detect.

Your car, like mine, has an open (not limited slip) differential. This is good while moving; loss of traction on one driven tire does not transfer all torque to the other tire and jerk the car sideways - especially if accelerating at the instant. Not so good if stopped and one tire is spinning on slippery stuff, in which case you get none or almost no torque on the other tire. This is called being stuck.
But your chains will solve that problem, if anything can.

Regards tires.
There is so much difference in wet, snow and ice performace between tires, even within the same performace group, that your experience will depend entirely on what you are now running. Search for tests, surveys and reviews at Tire Rack
http://www.tirerack.com/index.jsp
for an estimate of how your tires will perform.

My personal opinion is that driver experience and skill with ice and snow are as important as the tires. Some drivers can't stay in their lane with snow tires in 2 inches of the white stuff. Others manage just fine with all season or even summer tires in 10 inches. Of course if you want maximum performance and safety in snowy conditions, dedicated snow tires are the way to go.

Best of luck in Colorado. Your biggest challenge may be keeping your eyes on the road - the scenery is stunning.

See also:
- How does the BMW E39 fuel trim behave at high elevation (1) (2) (3) & where is the BMW E39 altitude pressure sensor (APS) (1)

Mine has been known to ask for a hoodie, a floppy wool cap, and some furry gloves.

Originally Posted by AnotherGeezer

Mine has been known to ask for a hoodie, a floppy wool cap, and some furry gloves.

Your whit charms me immensely.

Originally Posted by manticore33

Your whit charms me immensely.

Can I ask you something kinda personal? When BMW Mtech'd your rear....well, did it hurt?

Originally Posted by 540iman

Can I ask you something kinda personal? When BMW Mtech'd your rear....well, did it hurt?

Have you seen the hands of god? If so, it explains everything.

Originally Posted by manticore33

Have you seen the hands of god? If so, it explains everything.

I haven't seen him in awhile, but I do talk to him on a regular basis. Was not aware he was
still doing that procedure. If you happen to see God in the near future, will you see if he is still pissed at me?

Originally Posted by manticore33

Your whit charms me immensely.

I forgot to mention the fuzzy slippers.

Must haz fuzzy slippers.

The key thing is that the MAF (Mass Air Flow Sensor) reads the Mass of air entering the engine, so the signal it gives to the ECU already account of change in air density due to the altitude. The higher up you go the less air mass the MAF will signal to the ECU, so the less fuel the ECU will inject. The O2 sensors of course send fine tune to the ECU to adjust the air/fuel mixture which adjusts the short term fuel mixture adjustment, which over time adjusts the long term fuel adjusts.

Any Naturally Aspirated engine will lose noticeable power as you increase altitude (in my experience). Air gets thinner, oxygen is more scarce. Same effect as with temperature, the hotter the weather, the more power you lose due to thinner air. Although you may accelerate easier at really high speeds due to less resistance (not sure on that one).

According to information online, at 6000feet, air pressure is at 11.1 PSI, which is is a 25% drop. I'd say that you would experience pretty significant and noticeable power losses.

A turbo or supercharged car can combat the lack of oxygen as it can generate more boost than the turbo can use and the pop-off valve will actually release some of the oxygen back, but even F.I. cars will suffer some loss of power.

"Originally Posted by kross1300 View Post
I recently moved from San Diego to Breckenridge, CO and I have been having some trouble with how my car runs!

I would be pissed too, if somebody made me move from sunny SD to Colorado!

Originally Posted by BigCo540i

"Originally Posted by kross1300 View Post
I recently moved from San Diego to Breckenridge, CO and I have been having some trouble with how my car runs!

I would be pissed too, if somebody made me move from sunny SD to Colorado!

Colorado has more sunny days than CA. truth. CO. is as close to CA. as you can get which is why they call CO. "little California". Same freeky laws and politicians. I lived in both states and I'll take CO. ANYTIME! Colorado weather is awesome.

Originally Posted by 540iman

Colorado has more sunny days than CA. truth. CO. is as close to CA. as you can get which is why they call CO. "little California". Same freeky laws and politicians. I lived in both states and I'll take CO. ANYTIME! Colorado weather is awesome.

Who calls Colorado "Little California"? Not sure what freaky laws we have either...

OP, try driving to the top of Pikes Peak or Mount Evans, that's when you'll really notice you're down on power. Never had an issue with any of my vehicles ecus not adapting to the changes in elevation though, so if your car is stumbling, somethings not right. High reving NA vehicles aren't exactly the best for compensating for the altitude though, you'll find you need to keep the revs higher then at sea level and in a lower gear to make up for the loss in power.

regardless, with lower o2 content in the air due to higher altitude the engine operates less efficiently. It can compensate all it wants, less oxygen means less boom

Lol ya.

Altitude alone doesn't determine engine performance... nor does pressure or temperature.

The term is "DENSITY ALTITUDE" ... for all you aviation fans. It is possible to be at 6'000' and still perform as if you were at a lower altitude. Same holds true for the opposite.

Here is a calculator in case anyone is interested. Pretty straight forward. "Altimeter Setting" is your local atmospheric pressure (29.92 in. Hg is standard at sea level). You can get the required information from weather sources such as The Weather Channel.

http://wahiduddin.net/calc/calc_da.htm