Author Topic: Long term fuel trim  (Read 9043 times)

Panzermann

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Long term fuel trim
« on: August 09, 2013, 11:45:04 AM »
Closed loop fuel injection systems normally have among their adaptive values ‘long term fuel trim’. While Lambda values are available via the GS911, could long-term fuel trim also be retrieved from the engine management unit?

The reason I ask is I have a suspicion it may be the cause of an issue with the F800 where riders experience stalling when coming to idle after a long session of steady cruising, especially in warmer temperatures. Could the long-term fuel trim be leaning the mixture off to the extent that when you shut down to idle, the short-term fuel trim cannot adjust sufficiently?


Haakon

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Re: Long term fuel trim
« Reply #1 on: August 10, 2013, 10:03:28 PM »
Same problem on the early GS650`s when BMW had to modify the maps (to comply with Californian emission regulations)
2 modified maps made the bikes stall- some times causing dangerous situations!
The third map cured that:
More parameters were used to prvent that- brakes used, clutch disenegaged, throttle movement and so on.
When coming to a stop (throttle closed fast) AND the clutch is pulled the rpm drop in 2 stages.
First to 2200 and after a short time down to the normal 1700 idle rpm.
Its is strange they did not do the same on the (much more advanced) F800`s
I think you are right re the reason- a slow adaption and lean down action.
Have you checked if there are any modifications to the map on the F800?
Try do a realtime scan to see if the mixture lean out when riding at a steady speed .
     
2000 F650-GS

Panzermann

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Re: Long term fuel trim
« Reply #2 on: August 11, 2013, 07:55:55 AM »
Thanks Haakon for the background on the GS650.

Having read your reply and thought about it a bit more, I realise that the GS-9121 does read out fuel trim - depicting it as the Lambda Control Factor, although not breaking out a short and long term fuel trim. A data log of a long steady cruise (even commenced well into the run) should show whether there is a consistently low LCF emerging.

Fortunately I don't do such runs often (maybe once a year on a run from Canberra to Adelaide to see my Mum), much preferring the twisties. It might be a while before I get to do such a log (I don't feel like cruising for an hour at steady speed just as a test), but will certainly check this out when I get a chance.

Apparently the F800s have been subject to a number of software upgrades and so the problem appears to have been reported less often on the F800 owners forum. My bike hasn't been to a dealer for 4 years and 50,000 km, and so is still running probably 2008 software/fuel map. I have had only very rare instances of cutting out at clutch-in when coming to a stop, except for my last trip to SA, and so it isn't something I feel I need to solve for my bike as such - just curious to see if we could get to the bottom of it.

Other reported causes have been dirty/faulty idle actuator valve, kinked idle hoses, and faulty charcoal canister and/or vent tube (US models) perhaps caused by over-filling the tank,and poor fuel.

Where did you get your detailed info on the 650? It would be nice if BMW actually publicised what they do to software/map updates.

Haakon

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Re: Long term fuel trim
« Reply #3 on: August 12, 2013, 12:17:50 AM »
NOT GS911 material but I risk posting.
Long story: I have a "first" (2000) model F650GS and had my ECU software modified at the first free workshop session.
I was not asked- it just happened as part of the aftersale service.
The bike was then running like crap compaerd to what it was when I bought it.
Many people tried to get the old map installed but BMW central refused that.
So we started a group to try do it ourselves...... (Stephan was one of the group :-)
Part of the info can be found here:
http://geocities.ws/robertosat/ecu.html
---------
I do not suggest "bad" ECU maps are the problem but the description is familiar :-)
At the worst MY bike stalled when pulling the clutch after only 15- 30 minutes at a steady speed :-(
Now I have the original map and can do wheelies without even trying :-)))
And no hesitation or stalling, ever. The overall fuel consumption may be a bit more but only neglible.
Haakon 

2000 F650-GS

Panzermann

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Re: Long term fuel trim
« Reply #4 on: August 12, 2013, 11:54:50 AM »
Thanks Haakon - very interesting link. Kudos to all involved for sorting out the technicalities for the 650.