[aztechmaster]

During my clutch/trans output seal debacle, I decided to try something other than unplugging the air temp sensor. It seemed to use a bit more fuel and dirty the oil quicker, so what to do?

So I took some temp/resistance measurements, and it went like this-
33D-----------------5.12 kOhms
61D-----------------2.96 kOhms >all in F.
90D-----------------1.85 kOhms

I went to radio shack, got a pack of resistors, and added a 670ohm resistor to one of the wires inline. this effectively reduces sensor's true reading of air temp. Runs fine, and I will update as the weather improves, including mileage.

 

[Rocketsled]

During my clutch/trans output seal debacle, I decided to try something other than unplugging the air temp sensor. It seemed to use a bit more fuel and dirty the oil quicker, so what to do?

So I took some temp/resistance measurements, and it went like this-
33D-----------------5.12 kOhms
61D-----------------2.96 kOhms >all in F.
90D-----------------1.85 kOhms

I went to radio shack, got a pack of resistors, and added a 670ohm resistor to one of the wires inline. this effectively reduces sensor's true reading of air temp. Runs fine, and I will update as the weather improves, including mileage.

The problem, as I see it, is that BMW wouldn't have done what they did for no reason. It's an opinion I've formed over many many years of hotrodding cars.

Any 'simple' 'little' 'trick' to make more power usually bites me in the ass sooner or later.

The reason the bike gets doggy is that the ECU is pulling timing TO AVOID DETONATION. Detonation is BAD.

Now, as long as you've got good gas, and the motor is clean, and it's not 110 degrees in Death Valley, can you get by with LIEING to the computer about what the actual conditions are? Probably.

Is 'Probably' something you want to live with? Because stock motors seem to live for a VERY LONG TIME using the criteria BMW's driveline engineers came up with. The spent a long time with motors in many different configurations and environments and made a Calibration that will allow the motor to live in those environments. By removing the temp sensor input, you're kneecapping the ECU into making decisions it probably shouldn't.

Do I hotrod my stuff?....absolutely! But I've found you can't just do ONE thing when pursuing more power, you always seem to have to do things in pairs. So, pull the temp sensor and run premium? Okay. Assuming you ALWAYS have access to good premium, and you never ever ever run out of envelope...and you (or the next owner) always remembers you've pulled the temp sensor input.

Does pulling the sensor improve performance? I'm certain it does. But you're performing without a net, and without the ability to REALLY see what's going on, you'll never know how close you are to an expensive repair.

 

[johnbaker15]

I went to radio shack, got a pack of resistors, and added a 670ohm resistor to one of the wires inline. this effectively reduces sensor's true reading of air temp. Runs fine, and I will update as the weather improves, including mileage.

Just wondering how you picked 670 ohm, why not select a smaller resistance that would only offset the higher end temp calculations the ECU sees a little? See how it runs, adjust. Didn't do much math, but it looks like you kicked the 90 degree reading closer to 70 degrees, assuming the temp sensor is linear.

 

[BlauBeeMr]

:corn:

 

[deanwoolsey]

I can see the argument about messing with the O.E. systems but in this case adding the resistance tells the computer that it is cooler outside. Cooler = denser air = more fuel, correct? Besides, what I notice on mine is that this is a problem primarily at stop lights where the air flow is reduced and the intake is likely picking up artificially hot air off the engine. Once I get moving again the hesitation goes away.

 

[JPSpen]

OK, If I was gonna screw around with things. Hers's what I'd do..

Two ways to think about it... Put resistance in series and you can only increase the resistance.. Put resistance in parallel and you can decrease the resistance....

So maybe a couple of pot's across the thing.. One in series and one in parallel. Knobs up on the dash and a voltmeter across the sensor to see how you're affecting it...

I think this setup would probably give you the best chance at actually making a noticable change in the air/fuel mix....

And you might burn up your engine.... How fun ! :wave

John

 

[Rocketsled]

OK, If I was gonna screw around with things. Hers's what I'd do..

Two ways to think about it... Put resistance in series and you can only increase the resistance.. Put resistance in parallel and you can decrease the resistance....

So maybe a couple of pot's across the thing.. One in series and one in parallel. Knobs up on the dash and a voltmeter across the sensor to see how you're affecting it...

I think this setup would probably give you the best chance at actually making a noticable change in the air/fuel mix....

And you might burn up your engine.... How fun ! :wave

John

Wire in a knock sensor to a light while you're at it.

 

[Rocketsled]

I can see the argument about messing with the O.E. systems but in this case adding the resistance tells the computer that it is cooler outside. Cooler = denser air = more fuel, correct? Besides, what I notice on mine is that this is a problem primarily at stop lights where the air flow is reduced and the intake is likely picking up artificially hot air off the engine. Once I get moving again the hesitation goes away.

Hard to say without instrumentation. The intake being plastic shouldn't heat soak, and the horn being ahead of the radiators(?), and the fans pulling air past the radiators...it could go either way.

 

[jzeiler]

Just wondering how you picked 670 ohm, why not select a smaller resistance that would only offset the higher end temp calculations the ECU sees a little? See how it runs, adjust. Didn't do much math, but it looks like you kicked the 90 degree reading closer to 70 degrees, assuming the temp sensor is linear.

He did it correctly. With the resistor in series it would read "like" 70 degrees when it was actually 90. Thus preventing the high temp fuel map from kicking in. Great idea.

 

[Rocketsled]

He did it correctly. With the resistor in series it would read "like" 70 degrees when it was actually 90. Thus preventing the high temp fuel map from kicking in. Great idea.

Do you have to worry about throwing off an O2 sensor, clogging the cat, or fouling plugs?

 

[aztechmaster]

I spent 10 years in AZ, Maricopa county specifically- which I believe is the ONLY part of the USA that requires motorcycles to pass emissions testing. I did a LOT of emssions related reapirs on vehicles. (BTW, the 'H" brand RARELY passed) I have a four gas, portable(ish). With temp sensor unplugged CO was always high, over 4.5%. It would occasionally lean out to let O2 into the cat, so it would stay hot. But overall, used excesssive fuel.
The junction where NOX, CO, and HC work the best is very narrow. The only reason vehicles have rich/lean cycles is to allow the cat to operate as intended, Of course there are various other factors, such as fuel composition, different fuel maps for different loads and speeds. European cats very very rarely fail, as they have roughly three times the nessesary metals in them- and as a result will take much more abuse. (It is also why they are worth so much more to recyclers)
I do have a K&n air filter, which does let in a bit more air. So for now, the resistor is just trial size.
I have done this to other bikes, my own personal rides and others, and not one has destroyed a piston or tuliped an exhaust valve- in fact they passed emissions with BETTER numbers that stock. I think that is tuning!
If anyone is curious, I will report how it turns out.

Keep the rubber side down!

 

[Rocketsled]

(BTW, the 'H" brand RARELY passed)

I guess I'm not surprised, the stock pipes have cat matrix in them...but how many Harley's do you see with stock pipes? (my source is precisely one 95 Heritage Softail...it's stock pipes came with it, new in box.

 

[aztechmaster]

I guess I'm not surprised, the stock pipes have cat matrix in them...but how many Harley's do you see with stock pipes? (my source is precisely one 95 Heritage Softail...it's stock pipes came with it, new in box.

Didnt seem to matter, actually. Initially motorcycles had to pass an actual dyno run very similar to the IM240 test. After ruining many tires during testing and mixed results because so many testers coul not run bikes correctly (think of how different motorcycles are make and model versus cars) a new test was used- a simple idle test.

The idle test was started after 30 seconds of bike startup, then measured for about a minute the spec was less than 1600 HC ppm for most bikes. Which is far more than auto specs, which vary from 250 ppm to 450 ppm.

Plus, HD's dont like 119 degree, 9% humidity weather.Lost count of how many I saw barf oil out on hot days!

 

[New2rt]

During my clutch/trans output seal debacle, I decided to try something other than unplugging the air temp sensor. It seemed to use a bit more fuel and dirty the oil quicker, so what to do?

So I took some temp/resistance measurements, and it went like this-
33D-----------------5.12 kOhms
61D-----------------2.96 kOhms >all in F.
90D-----------------1.85 kOhms

I went to radio shack, got a pack of resistors, and added a 670ohm resistor to one of the wires inline. this effectively reduces sensor's true reading of air temp. Runs fine, and I will update as the weather improves, including mileage.

Spoofing is as old as Jetronic but if you must.
You can wire in the resistor to a 5 prong relay. Use 87a for the stock wiring as a failsafe, 87 for the resistor. You can select between the two on the fly.
You can use a GS911 to read the temp reading as you make changes.

If the butterfly flaps its wings it can lead to hot soak conditions, difficult to start, washed cylinders, carbon, etc. Depending on this application of Motronic you can bump against the adaptive limits as it tries to correct. I'm sure you're familiar with the ins and outs.

I gave up on this a long time ago, sometimes it was a hit, sometimes a miss.
Never better in all conditions. Seems to give a little to get a little.

Motronic generally leaned on the temp sensor 6%, you will notice the changes as the ambient temp. increases, not at all in cold ambient temps.

Have fun though.