Tuning K1100 engine by tricking air temperature sensor

[Juho]

Hi
I have k1100LT -92. I removed the air filter box and replaced it with individual air filters. I also cut the massive exhaust and replaced it with straight muffler.
So I guess that the engine is running a bit leaner now because it can breath a bit better than designed. I'm planning to trick the motronic to add more fuel by adding a resistor to the air temperature sensor.
I have read the ohm values for each temperature value from other topic, but I'm not sure how many degrees colder I need to trick the motronic, 5°C, 10°C, 15°C?

Does anyone have experience of this? I will get an adjustable trimmer resistor about 5k or 2k ohm so I can test run, adjust and check on spark plugs when the mixture is right but any tips would help really much. Thank you.

[blackie1]

Hi Juho,

over the years of reading very many posts on this forum I am aware that there are some exceptionally clever members on here that are very capable and expect you are possibly one of them.

i sadly am not.
  I have very limited expertise in anything mechanical. and can offer you no help at all. but perhaps can offer a light hearted distraction.

excuse my facetiousness ( but i cannot contain myself ) when i read in your query  "because it can breath a bit better than designed."
 
occasionally i stand in contemplation in my workshop, on the precipice of attempting a modification to my bike to improve it in some way and find that this often helps me in my decision making.

 i picture a team of bmw engineers who have spent countless hours designing my bike (albeit 30 years ago) who are perhaps specialists in their field, that have screeds of data and and every possible tool available at their fingertips.

then i look around my shed, 2x types of screw driver, a socket set, various bits of wood, a vice and a haynes workshop manual.

and although through the test of time certainly some design failures of the K bike have become evident, generally this contemplation has served me very well in the past and eventually my 2 x screw drivers will get put back in the kitchen drawer and I will don my helmet, push the start button once and will roar of out of my driveway to enjoy a fantastic ride on my slightly imperfect 32 year old bike.

I do wish you all success. I mean that.

facetious
adjective
treating serious issues with deliberately inappropriate humor; flippant.

[Chaos]

Hello Juho,

On my 87 K75s I replaced the airbox with a K&N pod filter, and ditched the stock muffler and have run several aftermarket pipes on it. Never messed with the fuel injection at all.  This was all done back in the late 80's or early 90's and several hundred thousand miles ago with no ill effects.  I don't think it really increased power much if at all but it looks cool.  Your bike has a later FI system so things may be different but generally it can compensate for slightly different airflow from intake or exhaust mods.

[Juho]

Hi Juho,

over the years of reading very many posts on this forum I am aware that there are some exceptionally clever members on here that are very capable and expect you are possibly one of them.

i sadly am not.
  I have very limited expertise in anything mechanical. and can offer you no help at all. but perhaps can offer a light hearted distraction.

excuse my facetiousness ( but i cannot contain myself ) when i read in your query  "because it can breath a bit better than designed."
 
occasionally i stand in contemplation in my workshop, on the precipice of attempting a modification to my bike to improve it in some way and find that this often helps me in my decision making.

 i picture a team of bmw engineers who have spent countless hours designing my bike (albeit 30 years ago) who are perhaps specialists in their field, that have screeds of data and and every possible tool available at their fingertips.

then i look around my shed, 2x types of screw driver, a socket set, various bits of wood, a vice and a haynes workshop manual.

and although through the test of time certainly some design failures of the K bike have become evident, generally this contemplation has served me very well in the past and eventually my 2 x screw drivers will get put back in the kitchen drawer and I will don my helmet, push the start button once and will roar of out of my driveway to enjoy a fantastic ride on my slightly imperfect 32 year old bike.

I do wish you all success. I mean that.

facetious
adjective
treating serious issues with deliberately inappropriate humor; flippant.

Well you got a good point there, bmw engineers probably knew what they were doing. Maybe I should just go for a ride and enjoy the bike, but it still bothers me that my modifications might have inbalanced the engine that the engineers have made.

Hello Juho,

On my 87 K75s I replaced the airbox with a K&N pod filter, and ditched the stock muffler and have run several aftermarket pipes on it. Never messed with the fuel injection at all.  This was all done back in the late 80's or early 90's and several hundred thousand miles ago with no ill effects.  I don't think it really increased power much if at all but it looks cool.  Your bike has a later FI system so things may be different but generally it can compensate for slightly different airflow from intake or exhaust mods.

My bike doesnt have the mass air flow sensor so i'm not sure if the engine knows how to compensate the muffler and filters as your bike does, or maybe the k1100 stock air flow is not so different compared to my current setup that it would make any difference. But as you said that you have not had any ill effects I can have a piece of mind knowing that the bike will run good even without my tune.

Although I will try the resistor trick to see if it makes any difference and update my results here.

[Laitch]

. . . you have not had any ill effects I can have a piece of mind knowing that the bike will run good even without my tune.
Although I will try the resistor trick to see if it makes any difference and update my results here.

The modification on Chaos's Brick is more basic than yours. His still uses the intake plenum that you have eliminated from yours. His still has the airflow meter and temperature sensor essential in the fuel calculations mounted in the only air intake. As you have noted, it's a different system.

You've significantly changed both the intake and the exhaust balance. Some who have modified the K1100 engine indicate that the length of the intake tubes has a significant effect on engine performance. Where did you mount the air temperature sensor? Your intention to try the "resistor trick" should be followed because you are charting a new course.

Have you read BMW's Motronic engine control manual? Click the link to it below.

[Juho]

The modification on Chaos's Brick is more basic than yours. His still uses the intake plenum that you have eliminated from yours. His still has the airflow meter and temperature sensor essential in the fuel calculations mounted in the only air intake. As you have noted, it's a different system.

You've significantly changed both the intake and the exhaust balance. Some who have modified the K1100 engine indicate that the length of the intake tubes has a significant effect on engine performance. Where did you mount the air temperature sensor? Your intention to try the "resistor trick" should be followed because you are charting a new course.

Have you read BMW's Motronic engine control manual? Click the link to it below.

Thank you for your reply, I'm happy to hear you confirm my concerns. I have the air filters attached to the original intake tubes. Do you have any info how the different intake tube lenghts affect the performance?

The air temperature sensor is mounted right under the air filters for now.

I have not had much time for the bike lately, but when i do I will test the resistors and possibly try the different resistors on dyno to see if there is any significant effect on power since I have seen these stage 1 (10hp-15hp) tune boxes on sale which are put on the air temperature sensor circuit.

Also thank you very much for the motronic manual, I will dive into it when I'm messing with the resistors.

[Laitch]

I have the air filters attached to the original intake tubes. Do you have any info how the different intake tube lenghts affect the performance?

My information about Brick performance and intake volume comes from my reading anecdotes from builders at various sites, but just putting the words intake tube length performance in a web search produces many research sources.