Why LT Runs Better In Cold? - BMW Luxury Touring Community
 
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post #1 of 18 Old Oct 8th, 2006, 9:37 pm Thread Starter
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Question Why LT Runs Better In Cold?

Greetings,

I have noticed that all summer my LT has been running a bit rough. Slow acceleration and surging at lower rpm, but normal above five grand. I completely went through the bike and everything appears normal. I was beginning to think the roughness was just in my mind. She seemed to idle a bit rough too.

Today, however, the outside temperatures dropped below 70 degrees. I went for a 50 mile ride and she is running great! Accelerating well at lower rpm, no surging, she feels like she weighs 60 lbs. lighter! Idles smoother too! There is a tremendous difference. Big smile!

Traveller is an '02 model. She has 43,000 miles. The brown wire is cut. This was a very hot summer. What would make her run better (or more normal) in cooler weather (70 degrees or less)? Is there a sensor that I should change? All regular maintenance is up-to-date.

I would appreciate any suggestions.
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post #2 of 18 Old Oct 8th, 2006, 10:54 pm
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Cold air is denser, so you are getting a richer mix. Same reason cars run better at sea level than 5000 feet.

Current rides:
2003 BMW 1200 LT (bought in 2006)

Past rides:
97 Kawasaki ZX11(bought new in 1997, sadly sold in September 2014)
89 Honda Hurricane (sold)
88 Honda Hurricane (traded on an SUV)
86 Kawasaki 1000R (stolen but recovered)
84 Honda 750F (traded on 1000R)
81 Suzuki GSX1100 (sold)
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post #3 of 18 Old Oct 9th, 2006, 2:19 am
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As above, all internal combustion normally aspirated motors run better in colder air because the air is more dense, and you are really getting more air into the motor. This is why some manufacturers have experimented with intercoolers to cool intake air, BMW being one of them.

Gary T
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post #4 of 18 Old Oct 9th, 2006, 4:37 am
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How well an engine runs depends a lot on the fuel/air ratio. Typically, Lts run on the rich side. When the ambient air temps are cooler, the air will be more dense. That increases the amount of air available and will LEAN OUT the rich fuel/air mixture. Manufacturers now this, therefore almost all vehicles are delivered to the masses with varying degrees of slightly rich fuel/air mixtures to insure the engines WILL NOT be harmed by a too lean fuel/air mixture. Many snowmobile owners (central Wisconsin) are aware of this and the oil injection pump output (two stroke engines) are also adjusted slightly high. It's a liability thing. Many high performance snowmobile owners will "lean out" their machine's fuel/air ratio AND oil injection pump output after engine breakin. That is the main reason snowmobile owners love to get out on those crisp -20 degree nights here in Wisconsin.

Some people don't ride snowmobiles, we fly them.
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post #5 of 18 Old Oct 9th, 2006, 7:01 am
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Seems like my 03 LT is running rougher now that the weather has changed. Have not cut brown wire. I am using premium gas. I'm thinking it's mostly related to just being cooler. Runs fine once it warms for a few minutes.

Rando.
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post #6 of 18 Old Oct 9th, 2006, 7:12 am
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Talking Why LT runs better in the cold?

Allen, I suspect that the problem is the cigars that you are smoking! What is happening is that the smoke from the cigar is being taken into yours and the bikes air intake system and is blending with the fuel air mixture causing a "roughness" to the iding of the bike and your brains performance. The quick solution to the problem would be to change to a more expensive "Havanna cigar". I understand that they come with a higher octane rating and will make you and the bike feel lighter and therefore faster! Just a thought. Ha!Ha! Your buddy, Ron

Ron Ray
Lexington, South Carolina
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post #7 of 18 Old Oct 9th, 2006, 9:13 am
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A couple of answers were close, but slightly off. When it is colder, the denser air causes an increased mass of air to be inducted into the cylinders. The mixture will not be leaner or richer though, because the Motronic controls the mixture based on the readings from the O2 sensor. More power will be produced because of the larger total mass of the mixture though.

The reason we get such great fuel mileage at high altitude is because of the reduced mass of air inducted, and the lower quantity of fuel injected to keep the mixture correct. Of course there is also less power.

I don't want to achieve immortality through my work...I want to achieve it through not dying.

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post #8 of 18 Old Oct 9th, 2006, 9:50 am Thread Starter
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Thumbs up Grand Idea!

Quote:
Originally Posted by ronlray
The quick solution to the problem would be to change to a more expensive "Havanna cigar".
Grand idea! I will go out and grab one of my Cubans right now! Will let you know!
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post #9 of 18 Old Oct 9th, 2006, 10:03 am
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I thought I read somewhere on this board that some dealers actually disconnect the IAT (Intake Air Temperature) sensor wire. Not sure exactly where it is, but I believe it cured the symptoms you are having, but it will show an error code on the Moby Dick. I also have an '02 and cutting the brown wire fixed mine.
Anybody else remember this?

-Brian Louw
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post #10 of 18 Old Oct 9th, 2006, 10:19 am
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Quote:
Originally Posted by blouw
I thought I read somewhere on this board that some dealers actually disconnect the IAT (Intake Air Temperature) sensor wire. Not sure exactly where it is, but I believe it cured the symptoms you are having, but it will show an error code on the Moby Dick. I also have an '02 and cutting the brown wire fixed mine.
Anybody else remember this?
That was a common fix for the hot hesitation in the early LTs, before the updated Motronic was introduced.

DO NOT do that on a late '01 up though if the brown wire has been cut!!!

I had done that on my '01, which had the updated motronic and had also had the Cat Code plug removed by the dealer. (Removing the Cat Code plug on the early ones was the same as cutting the brown wire on later ones).

I think that may have contributed to my detonation damaged pistons when I had the misdiagnosed vacuum leak.

Basically, either remove the air box temp sensor, OR cut the brown wire, but do not do BOTH!

I don't want to achieve immortality through my work...I want to achieve it through not dying.

David Shealey
Dandridge, TN
EX: '01 Black LT, BAT BYKE (Totaled at 110,000 miles)
IBA SS, BB, BBG, 10/10ths.
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post #11 of 18 Old Oct 9th, 2006, 10:23 am
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Thanks for the info, David.
That explains why it cured mine.

-Brian Louw
Arroyo Grande, CA.

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post #12 of 18 Old Oct 9th, 2006, 4:55 pm Thread Starter
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Question

Quote:
Originally Posted by dshealey
Basically, either remove the air box temp sensor, OR cut the brown wire, but do not do BOTH!
Basically, my bike is running (in hot weather) as if the brown wire was not cut. That best describes the symptoms. There is such a difference in hot/cool weather running that I'm convinced something is not quite right.

I checked the brown wire, just in case, it is still cut and not touching. I also had a dealer put it on his computer this summer. All checked out a-okay.
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post #13 of 18 Old Oct 9th, 2006, 7:25 pm
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No AC

You don't run the AC at 70 degrees
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post #14 of 18 Old Oct 9th, 2006, 8:36 pm
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>The reason we get such great fuel mileage at high altitude is<

Higher altitude = less dense air = less aerodynamic drag, and
Higher altitude = less pumping loss in the engine from intake throttling.

The aerodynamic drag at 6500 ft elevation is about 82% of the sea level drag.

Higher temperatures will also improve fuel economy because of reduced air density.

The Motronic fuel injection system uses the O2 sensor in the exhaust to maintain the fuel-air mixture such that essentially all of the fuel is burned for maximum efficiency and minimum emissions.

Aircraft pilots use these parameters to reduce fuel consumption, too. It doesn't matter that we are on two wheels, the rules stay the same.
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post #15 of 18 Old Oct 11th, 2006, 9:34 pm Thread Starter
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Cool

Quote:
Originally Posted by DaveDragon
There's the problem, only 43,000 on an 02 model
Dave,

Traveller is my Garage Queen. We only take her on trips, double-up. My RT is my daily rider
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post #16 of 18 Old Oct 12th, 2006, 11:41 am
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hesitation

Did you ever have your bike checked under the "hot ambient hesitation" recall? Or does the cut brown wire take care of that, I don't know. Incidentaly, there is another reason for improved fuel economy at high altitude. Air: 359 cubic ft. = one Lb. mole (aprox. 28 lbs.)at sea level and STP. So at high altitude, you are moving significantly LESS lbs. of air out of the way as you motor along. This is a strong enough effect that it is noticable on old K-bikes (K75 and K100) even though their mixture is way too rich at high altitude!
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post #17 of 18 Old Oct 12th, 2006, 3:31 pm
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I am not on that often and have been reading this thread, so I will have to ask a question that may seem old, what brown wire are you talking about that has been cut?

Laster
02 BMW LTE

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post #18 of 18 Old Oct 21st, 2006, 10:33 pm Thread Starter
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brown wire........

Quote:
Originally Posted by Laster
I am not on that often and have been reading this thread, so I will have to ask a question that may seem old, what brown wire are you talking about that has been cut?
Laster,

The '02 models are apparently fuel injection mapped for Germany. If you live in an area with high temps/humidity (Bible belt) there is a second fuel injection map available.

To get the second map, the '02 LT has a brown wire loop just under the seat. You clip/cut this wire and the LT goes to the second mapping.

This is invaluable for the '02. Without it, the LT surges and operates poorly at low rpm in the summer months.

Sorry it took me so long to get to this, I've been riding the mountains for a while.
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