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What an unbelievable difference unplugging the airbox temp sensor makes!

24K views 35 replies 25 participants last post by  saddleman 
#1 ·
Yesterday in the 100F heat I unplugged my temp sensor and WOW-O-WOW what a difference it has made!! :dance: I can very honestly say that in the last two months my bike has never ever run this good! THIS is what a BMW is supposed to be like!! WAHOO!!! With the way it runs now I don't think it ever did not have the hesitation issue. Now I have to learn to drive it slow again because the ol girl really wants to go! If you are reading this and have not learned your lesson on your own take it from me and many others... get your butt out there and unplug the anchor! Makes me want to ride all the more... OHYEAH!!!! :D
 
#2 ·
i remember in a not to distance thread on pinging or the brown wire. mr ziegler wrench extrodinare said somthing to the affect of do not unhook air temp sensor possible internal engine damage or somthing to that affect.he will prob comment on this thread.or you may want to send him a PM.
 
#3 ·
Bob, I am not John Z, and I did not sleep at a Holiday Inn Express last night, but my name is John, and I believe you may have gotten confused on the difference between the early LT's and the later ones. Not sure when they started providing the loop in the famous Brown Wire which can be snipped to prevent the hot weather hesitation issues, but the early LT's did not have the Brown Wire loop. So the early LT's cure for that hesitation was to disconnect the Airbox Temp Sensor, as the OP here did.

The warning for either method is that you should use only premium grade fuel thereafter due to the change in fuel mapping. And certainly, if your LT is one of those later ones with the Brown Wire which you have snipped, you do not need to disconnect the Airbox Temp Sensor!

HTH,

John
bobst2 said:
i remember in a not to distance thread on pinging or the brown wire. mr ziegler wrench extrodinare said somthing to the affect of do not unhook air temp sensor possible internal engine damage or somthing to that affect.he will prob comment on this thread.or you may want to send him a PM.
 
#4 ·
+1 on John F's explanation. As mentioned, there are a bunch of early model year LTs running around with the airbox temp sensor removed. It wuz a welcome tip from (I think, IIRC) Mark Neblett back in the day, and like the OP sez, it resulted in a new ride and took the worry away regarding leaving cleanly from the starting line.
 
#5 ·
Had modified mine splicing one lead threw a switch mounted top of stingray. A/B sensor on in sub 80* and off above that.
It has worked out very well rigged this way :wave
 
#6 ·
What I said was don't cut the brown wire (if you have one) AND pull the air temp plug at the same time. One or the other by itself is OK. Both gives you a too lean issue that can cause detonation (even on premium) that will damage the piston ring lands. Seen this in at least two engines so far.
 
#7 ·
jzeiler said:
What I said was don't cut the brown wire (if you have one) AND pull the air temp plug at the same time. One or the other by itself is OK. Both gives you a too lean issue that can cause detonation (even on premium) that will damage the piston ring lands. Seen this in at least two engines so far.
My Y2K pings on premium fuel when modestly warm and at lower rpm under a load no matter A/B switch position .
No oil burning happening but then again don't see myself pulling engine apart to look.
 
#8 ·
I have an 06 LT and not sure where this plug is. I looked under the fairing on the left side (while facing the front of the bike) and don't see anything close. I don't have a left radiator cap, but just a connector hose to the right side. When others said "left side", did they mean when sitting on the bike or standing it front of it.

I live in GA and the temps are always in the high 80's, 90's and 100's in the Summer. I would like to try this mod. Will my gas mileage suffer any? I like the 46 - 50 MPG I get now.

Thanks everyone!
Sammy
 
#10 ·
I have a 2001 LT and I just removed the Cat Code plug under the trunk, also did the cannisterectomy while I was in there. I posted pics under the "Just where is this fabled brown wire" thread.

Been running premium ever since and have not noticed any pinging the it definitely doesn't bog anymore like it did.
 
#12 ·
14wntr said:
Yesterday in the 100F heat I unplugged my temp sensor and WOW-O-WOW what a difference it has made!! :dance: I can very honestly say that in the last two months my bike has never ever run this good! THIS is what a BMW is supposed to be like!! WAHOO!!! With the way it runs now I don't think it ever did not have the hesitation issue. Now I have to learn to drive it slow again because the ol girl really wants to go! If you are reading this and have not learned your lesson on your own take it from me and many others... get your butt out there and unplug the anchor! Makes me want to ride all the more... OHYEAH!!!! :D
I agree, it was like night an day for me too in hot weather after I disconnected the temp sensor on my 99LT. I eventually put a switch to be able to connect/disconnect the temp sensor thinking that in cold weather it would run better and would get better MPG with the temp sensor connected back but I did not see any difference so now it is off all the time.
 
#13 ·
So I'm told that the 06 LT's do not have this plug / brown wire. So we don't have a way to alter the mapping in hot weather? Just curious. I see a plug next to my left (sitting on the bike) radiator cap, but I guess it's not the right plug for the airbox temp sensor.

Thanks for the guidance,
Sammy
 
#14 ·
Here in Finland hot weather is not that common problem BUT this and past summer have had days with >30C. I noticed clear difference / stalling above 2kRPM when the temperature was >28C. After reading these "brown wire" and "air temp sensor" threads from this site I installed a switch in my -99LT's temperature switch wire. As the one starting this thread said - WHAT A DIFFERENCE! Haven't turned that switch on since I cut the line... :)
 
#16 ·
14wntr said:
Yesterday in the 100F heat I unplugged my temp sensor and WOW-O-WOW what a difference it has made!!
I was just thinking about this problem. I have read many posts about canisterectomy, cutting the brown wire and unplugging the air temp sensor wire. I have not found a single message about finding and fixing/replacing the culprit part. There is of course a problem or we would not have this many fixes for the same symptoms. So what exactly is the problem and why is there no BMW supported fix for the problem?

Has BMW ever acknowledged the existance of symptoms (stalling) and offered to replace a part? I too have a 2000 LT with the same symptoms and I am going to unplug the air temp sensor this weekend. But would a new air temp sensor also fix the problem? Or does the fuel map need to be updated?

Please don't misunderstand. I am happy that someone (probably several of you) identified the symptoms and tried the three aproaches mentioned above and passed along your new found information. Thank you for doing that. I could not have done what you have done for I have not the knowledge. It just seems that there should be a BMW "authorized" fix. Am I way off base here?

Jonny Oliver
Concord, NC

1993 K1100LT
2000 K1200LT
 
#18 ·
The motronic unit was upgraded I think 3 times in the 10 year run the LT has had. With temperature and humidity being such a large contributor in combustion efficiency and this being so varied world wide ... issues that we read about IMO are pretty spotty at best.

Because so much of the finer details get left out in posts ... Running shit fuel, Have a Remus exhaust, fiddled with this and fucked with that get left of of posts, one somewhat has to read between the lines.

I'm guilty ... have a Remus and no chip upgrade, bike runs great !!, but pings when hot on premium fuel ... NO MATTER WHAT !

So I rev higher and shift later ... problem solved.

Hope you see my point ;)


joliver said:
I was just thinking about this problem. I have read many posts about canisterectomy, cutting the brown wire and unplugging the air temp sensor wire. I have not found a single message about finding and fixing/replacing the culprit part. There is of course a problem or we would not have this many fixes for the same symptoms. So what exactly is the problem and why is there no BMW supported fix for the problem?

Has BMW ever acknowledged the existance of symptoms (stalling) and offered to replace a part? I too have a 2000 LT with the same symptoms and I am going to unplug the air temp sensor this weekend. But would a new air temp sensor also fix the problem? Or does the fuel map need to be updated?

Please don't misunderstand. I am happy that someone (probably several of you) identified the symptoms and tried the three aproaches mentioned above and passed along your new found information. Thank you for doing that. I could not have done what you have done for I have not the knowledge. It just seems that there should be a BMW "authorized" fix. Am I way off base here?

Jonny Oliver
Concord, NC

1993 K1100LT
2000 K1200LT
 
#19 ·
My 99 has a Remus exhaust and a Rhinewest performance chip up grade. It runs fine on even 87 octane with ethanol although seems to like mid grade gas better so that is what I use. I get a very slight hesitation at times around 2500 rpm and I get some popping on deceleration. My gas mileage is only 42mpg. None of these symptoms bothers me at all.

I try to buy fuel at high volume name brand gas stations to hopefully get clean fuel. I put a dose of Seafoam in the tank every so often and all is well. Just my 2 cents worth. :cool:
 
#21 ·
This has been discussed probably a hundred times or more, starting in early 2000. I posted several times about the issue, and think I had detonation damage on all four pistons from both removing the Cat Code Plug AND unplugging the air box sensor for a short time on my early 2001 LT. Here is the most recent post I did on the subject:

http://www.bmwlt.com/forums/showpost.php?p=539146&postcount=11

In short, there is no simple answer on when or how you should make a modification, it depends on the year of your bike, and which Motronic is installed. Be warned, doing it wrong can lead to real problems.
 
#22 ·
dshealey said:
This has been discussed probably a hundred times or more, starting in early 2000. I posted several times about the issue, and think I had detonation damage on all four pistons from both removing the Cat Code Plug AND unplugging the air box sensor for a short time on my early 2001 LT. Here is the most recent post I did on the subject:

http://www.bmwlt.com/forums/showpost.php?p=539146&postcount=11

In short, there is no simple answer on when or how you should make a modification, it depends on the year of your bike, and which Motronic is installed. Be warned, doing it wrong can lead to real problems.
Thank you, Mr. dshealey. Your last post (url above) is exactly the information that I was looking for. This site is so volumous that it is hard to see every post on a particular topic that you are interested in. It must be an absolute horror to monitor and classify. Thank you again for kindly sending the url to me.

Jonny Oliver
1993 K1100LT
2000 K1200LT
 
#23 ·
For what it's worth...........

The Clymer manual says that the air inlet temp sensor is used by the Motronic to determine air \ fuel mixture - and - ignition timing.

The sensor is an " NTC " ( negative temperature coefficient )
The resistance of the sensor decreases as temp increases.

So I guess that the logical conclusion is that by showing the Motronic an open circuit, it's seeing high resistance......a very cold air box.......no need to retard timing to avoid detonation ?
 
#24 ·
Sorry to pull this one back to the surface... I've been reading and searching to determine which model years this effects. As in, which models have the brown wire, which have the cat code plug, etc. I know all of them would have the temp sensor. I have an '09 that has a minor hesitation in high temps. I'm assuming (since it's an '09) it would have the latest and greatest Motronic unit. Would any of these methods help out this model year...? Any further info would be greatly appreciated - THX!

Mark
 
#25 ·
These were all pre-05 fixes for the fuel map. The 05 came with RS pistons and larger throttle bodies and thus a new fuel map. I have not experienced it with my 05 in 73K. Have not seen any mention of it here either. I presume you are running premium fuel.
 
#26 ·
I have a 2002 LTE and am new to this bike. Please excuse my ignorance, but where is this brown wire/loop. I observed a brown wire under the front seat that was not attached to the battery ground, is this the culprit everyone speaks of? When I replaced the battery I connected that wire to the ground, did I make a mistake?
 
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