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Discussion Starter #1
I've got a fuel injection mapping problem on my 2000 LT which appears to be related to the timing of the cooling fans.

Both the water temp gauge and the ambient temp on the LCD are functioning normally. What is happening which is not normal is that the cooling fans are starting up just after the water temp gauge passes the center "nominal" mark.

When the fans kick in the Motronic appears to also set the mixture richer to avoid pinging. That would be a good thing if the fans kicked in normally just below the red line, but with the engine at normal temps the mixture is too rich and the engine stumbles and will die at idle. But if I kick up the RPMs to the 5,000 range the Motronic seems to remap itself out of the situation and the bike purrs like a kitten. Also if I turn the key off and on the Motronic seems to reset and the bike will start and idle OK. Those things combined seem to rule out the usual suspect, the O2 sensor.

The problem gets worse when the ambient temp climbs above 90 F degrees (per the LCD temp readout). I'm aware of now the Motronic richens the mixture under 3,000 RPM at ambient temps above 90 F, so I removed the yellow jumper plug to see if that would affect it in any way. It didn't as far as I can tell.

By my reckoning all signs seem to point at temperature sensor problem which is causing the fans to come on prematurely creating the domino effect with the injection mapping. I understand from a previous thread the Motronic controls the fan relays, but I can't pin down what temperature sensor triggers the Motronic to turn them on. It doesn't appear to be the water temp sensor or the sensor running the LCD temp.

Is there another air sensor somewhere such as in the plenum for the air intake which controls the cycling of the fans?

Do you think the problem might be a defective fan relay?

Any clues or hint appeciated.

Chuck Gardner
Manassas, VA
 

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Shot in the dark, but it may be a defective temperature sensor relay. Although your temperature guage seems to run nominally, a different signal may be getting sent to the control box.

Any air in the cooling system ? If so, this can also cause a false temperature reading, sounds funny, but this can cause confusing temerature readings also.


Like I say, shot in the dark.
 

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Chuck, you are right that the OBC LCD temp readout has no relation with the fan operation, nor the Motronic. I would think for sure that the fan operation would be determined by the circulating water temperature, which is gauged by the water temp sensor located just above the left radiator. The injection mapping is controlled, in part, by the incoming ambient air thru the airbox, wherein lies the O2 sensor (I think). There is more to it than this, but I'm not qualified to know what!!! On ole Toad, removal of that O2 sensor in-line connector invoked the running of only one injection mapping program, which did not get changed when the ambient air temp rose above ~86 degrees F.

I would think, however, that both the fan engagement threshold, as well as the fuel injection mapping, have parameters that can be set using a dealers MoDiTec unit. May be wrong on both counts there, and I hope one of the gurus will straighten me out, as well as git you some better info.

One other thang - I don't know if this would help, butt you might try either disconnecting the battery for a period of time over 15-20 minutes (or pulling the bottom fuse in the far right fuse box under the pillion seat), then connecting everythang back. Then do the TPS re-setting procedure:

Key on - no start.
Twist throttle to WO and release, twice.
Key off.
Start the bike and take a ride.

Good luck to ya, Chuck. Stay tuned for the experts!!
 

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The yellow jumper may be the catcode plug and you may need to hook it back up. If your bike does not have the newer dual mapping software (which mine does not) you need to keep that plug installed. My bike had some hot weather issues (as in dam near tossed me off when the engine caught all of a sudden in a turn) and the dealer disconnected the air filter air temp sensor.

The above is just a guess based on my limited working on my ride and what I have read on this site - some of which I may have totally misunderstood.
 

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NOT a Motronic guru

... and I did not sleep at a Holiday Inn last night. However, from what I can understand of the wiring schematic from the Clymer manual, for "2001-on LT Engine" there is both an air temp sensor (not the ambient temp thermometer) and a coolant temp sensor. Both connect directly to the throttle potentiometer (possible source of enriched mixture?) and to the Motronic via a brown/yellow wire at pin 22. Pin 17 of the Motronic connects to the Fan Relay via a blue/yellow wire. The air temp sensor in on the front of the air box, above and slightly behind the left radiator. It's plausible that that is the source of your problem. According to the Clymer manual, "The input from this sensor is used by the Motronic control unit to determine the air/fuel mixture and ignition timing for optimum performance." IIRC, on early LTs the air/fuel ratio was enriched in hot weather, causing the infamous "hesitation" when accelerating from a stop. Because I do not have the "brown wire" to snip on my bike (1999 LT), the next best fix for hot weather hesitation when accelerating from a stop was to unplug the air temp sensor completely. I did that, and it has eliminated the hesitation, with no adverse effects on any other function that I have noticed. If you have skinny long fingers and don't mind putting several of them out of joint, after removing the left side upper fairing it is just possible to get to the air temp sensor and unplug it without removing the stingray and dashboard and nose cone. Or so I'm told. I pulled mine when I had all the tupperware off.

However, I think it is more likely that your problem with the fans being triggered too early is due to a bad coolant temp sensor. According to the Clymer manual, "The fan is controlled by the Motronic unit, fan relay and the coolant temperature sensor." The fact that your fans come on early makes me suspect the coolant temp sensor. It is located on the oil/coolant pump, close to the oil temp sensor.

Clymer says only the MoDiTec at your dealer can test these sensors. You could unhook the air temp sensor and run the bike to see if that makes any difference; probably have to take the tupperware off on the left side, along with the dash and perhaps the nose cone, to plug it back in, though. If you remove the coolant temp sensor you will dump coolant on your garage floor and won't be able to test the bike, so that one probably does require a MoDiTec. Good luck!
 

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Discussion Starter #6
Good clues...

lnowell said:
The yellow jumper may be the catcode plug and you may need to hook it back up. If your bike does not have the newer dual mapping software (which mine does not) you need to keep that plug installed. My bike had some hot weather issues (as in dam near tossed me off when the engine caught all of a sudden in a turn) and the dealer disconnected the air filter air temp sensor.

The above is just a guess based on my limited working on my ride and what I have read on this site - some of which I may have totally misunderstood.
Could you or anyone else elaborate on the air filter temp sensor? That's sounds like exactly the suspect I am looking for.

Where is it?
What is its role with respect to the injection mapping?
How do you disconnect it?
Is there any downside to disconnecting it?

Thanks,
Chuck
 

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Discussion Starter #7
was said:
..The air temp sensor in on the front of the air box, above and slightly behind the left radiator. It's plausible that that is the source of your problem. !
Seems to be at least part of it..

was said:
..
According to the Clymer manual, "The input from this sensor is used by the Motronic control unit to determine the air/fuel mixture and ignition timing for optimum performance." IIRC, on early LTs the air/fuel ratio was enriched in hot weather, causing the infamous "hesitation" when accelerating from a stop. Because I do not have the "brown wire" to snip on my bike (1999 LT), the next best fix for hot weather hesitation when accelerating from a stop was to unplug the air temp sensor completely.
Mine is a 2000 which doesn't have the brown wire either. I removed the yellow plug, which I thought did the same thing as cutting the wire on a 2000.

was said:
..
However, I think it is more likely that your problem with the fans being triggered too early is due to a bad coolant temp sensor. According to the Clymer manual, "The fan is controlled by the Motronic unit, fan relay and the coolant temperature sensor." The fact that your fans come on early makes me suspect the coolant temp sensor. It is located on the oil/coolant pump, close to the oil temp sensor.
What seems to argue against that is the fact the guage reads normally, its just that the normal signal level from the gauge seems to be triggering the fan relays prematurely even in the dead of winter.

The fans coming on early actually started more than a year ago long before the too rich mixture started occuring. I didn't bother to get it fixed because on a 100 degree day at a traffic light having the fans come on early was a good thing. The gauge never even comes close to the red zone that way.

was said:
Clymer says only the MoDiTec at your dealer can test these sensors. You could unhook the air temp sensor and run the bike to see if that makes any difference; probably have to take the tupperware off on the left side, along with the dash and perhaps the nose cone, to plug it back in, though. If you remove the coolant temp sensor you will dump coolant on your garage floor and won't be able to test the bike, so that one probably does require a MoDiTec.
First I think I'll try removing the Motronic fuse and reset it. Once I determine if it makes any difference or not I will next try disconnecting the air temp sensor and see what happens. Thanks for the advice.

Chuck
 

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See post by "was". He is way beyond me. I did not have ANY idling or crusing issues with my bike. My issue was with the engine dying when accelerating at the lower RPM range and suddenly coming alive (as in - hold on alive). Happened only when hot - 90+ degrees. It made no difference what the engine temp was - so it must have been the air temp sensor - BUT again - no issue with idling at all. I still think yout issue is with the version of the mapping software or the missing yellow catcode plug.
 

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Chuck_Gardner said:
Could you or anyone else elaborate on the air filter temp sensor? That's sounds like exactly the suspect I am looking for.

Where is it?
What is its role with respect to the injection mapping?
How do you disconnect it?
Is there any downside to disconnecting it?

Thanks,
Chuck
Look behind the top of the left radiator. There is a plug there. That's the intake air temp sensor. I had mine unplugged on my 2000LT for years without any detriment. Fact is, Tom Lawrence, a then BMW honcho, told us it was an acceptable fix for warm weather stumble. Unplug that puppy.



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The ECU turns the fans on anf off using data from the coolant temp sensor. A bad coolant temp sensor will also cause the ECU to program in too much fuel or not enough (depending on what readings it is giving) and this will cause knocking and or stumbling of the engine.
 

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Morley said:
The ECU turns the fans on anf off using data from the coolant temp sensor. A bad coolant temp sensor will also cause the ECU to program in too much fuel or not enough (depending on what readings it is giving) and this will cause knocking and or stumbling of the engine.
It would be first that I've heard of on these bikes. Though it wouldn't hurt to try. Another thought along this line would be to check the connection to the sensor for corrosion and/or damage.



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Temp Sensor

IIRC there are two coolant temp sensors on the LT. The one on the water / oil pump is used to control the level of the water temp gauge.
The second is mounted in the rear of the cylinder head (down by your left foot peg) and is used to provide information to the motronic. If this one were out of spec it is possible to cause the problem you describe and not have any effect on the gauge reading.

HTH and Good Luck



Edit: For you with the Clymer manuals see page 255 illustration 60.
 

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Dman said:
IIRC there are two coolant temp sensors on the LT. The one on the water / oil pump is used to control the level of the water temp gauge.
The second is mounted in the rear of the cylinder head (down by your left foot peg) and is used to provide information to the motronic. If this one were out of spec it is possible to cause the problem you describe and not have any effect on the gauge reading.

HTH and Good Luck



Edit: For you with the Clymer manuals see page 255 illustration 60.
Good catch! This had confused the hell out of me, so I ignored it, hoping it would go away, but I think you have it. On closer reading of the manual, there is a coolant temperature switch at the water pump and a coolant temperature sensor screwed into the engine. (In some places, Clymer refers to the latter as the "engine temp sensor.") "The input from the sensor (italics mine) is used by the Motronic control unit to determine the air/fuel mixture and ignition timing for optimum performance." (Clymer, p. 255). Part of what makes this confusing is that Clymer's electric schematics identify both of these parts as "Coolant temp. sensor" (pp. 599 and 601), but I think it is safe to ignore that. So, the air temp. sensor on the air box and the coolant temp sensor on the engine both send information to the Motronic, which uses that information to map air/fuel mixture and ignition timing. The info from the coolant temp sensor also is used by the Motronic to activate the cooling fans on the radiators. Info from the coolant temp switch goes to the (engine) temperature gauge on the dashboard. Thanks again for clarifying this.
 

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Dick said:
One other thang - I don't know if this would help, butt you might try either disconnecting the battery for a period of time over 15-20 minutes (or pulling the bottom fuse in the far right fuse box under the pillion seat), then connecting everythang back. Then do the TPS re-setting procedure:

Key on - no start.
Twist throttle to WO and release, twice.
Key off.
Start the bike and take a ride.

Good luck to ya, Chuck. Stay tuned for the experts!!

I was looking up a problem with my 99LT and this procedure really helped.
My bike was cutting out constantly at low throttle ( To Rich I think). It was very smokey constantly, loss of power AND stinky for some reason. After I did this I had my old bike back again! Thx dick :toast:
 
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