Lamba and Closed Loop Control

Grizzly

Grizzly

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Hi, My 2001 1150GS is running sweet and fuel consumption is about the same, but idle has probably not been as smooth as it used to be.
I hooked up my GS-911 and no ecu faults logged - which is good news, however, when monitoring lamba voltage (ie O2 level) it is "flat-lining" and in the realtime data lists the Lamba closed loop control is shown as OFF - this is true with engine cool and also when fully warmed up with a road run and engine temp showing 90 degr.
Any suggestions - is lamba likely to be ok but system not switching into "closed loop control" -why?.
I expect it to flat-line when cold then closed loop control should switch on and cause the graph to show a "saw-tooth" graph as mixture is controlled by lamba.
Any suggestions???

Cheers...................Grizzly
 
Could be a knackered lambda sensor. Get someone to check it with a scope.
 
Not unusual to go open loop on idle - even when hot. Does the voltage start to fluctuate when you go on fast idle - say 2500rpm? If the O2 sensor is permanently dead, the ecu will flag up a code. You can test the output with any voltmeter - if it jumps wildly between about 0.2 and 0.8 Volts (on steady throttle), it's working.

BTW, if you decide to change the sensor, fit a decent one - NTK or Bosch.

Ask if you need any more help :)
 
Thanks for replies. Lamba voltage just sits steady - may "creep" up or down slightly but generally seems to creep up to about 0.9V but no fluctuations from 0.2 to 0.8 as you would expect - revving engine may cause slight creep up or down but no spiking.
I can plug the GS-911 into my K1300GT and it behaves as expected - flat-lining graph when cold then spiking 0.2 to 0.8 when warm - but I'm sure the "closed loop control" also switches from "off" to "on" but on the 1150GS the closed loop control is always "off" - even when oil temp input is at 90 deg - what switches the closed loop control "on" - is it the ECU based on engine(oil) temp or is it something to do with the lamba - ie is it hot enough?
Although possibly not relevant, it's the original-fitment Lamba - which has now done 172K.

Cheers.......................Grizzly:beerjug:
 
I would start with the basics mate, throttle body sync, valve clearances, O2 sensors are pretty robust as long as it's not been poisoned



Sent using witchcraft
 
Basics Spot On

All basics are spot-on, Throttle body sync, valves, tps etc, etc. To me they wouldn't/shouldn't stop the lamba from going into a closed loop control anyway:confused:

Cheers.........................Grizzly:beerjug:
 
Grizzly said:
All basics are spot-on, Throttle body sync, valves, tps etc, etc. To me they wouldn't/shouldn't stop the lamba from going into a closed loop control anyway:confused:

Cheers.........................Grizzly:beerjug:
Click to expand...

Are you sure it should be closed loop at idle??
Would not be the first to chase a fault that isn't a fault at all
I am not sure either way but some clever sod will



Sent using witchcraft
 
More Info

Ok, after reading Uncle Dicks info, I persevered testing Lambda control on the GS-911 & laptop. Eventually got the "closed loop" to come "on" by holding a (very) steady 2500rpm and the lambda voltage then starts to oscillate between 0.2 and 0.8 as it should - quite difficult to keep it "on" but volts oscillating as expected when "on".
So, lets assume Lambda is OK:thumb - BUT when I start the engine again the Lambda voltage flat-lines around 0.5v at idle (open loop) but very slowly ramps up to around 0.8-0.9v - ie too rich. When I provoke closed loop by holding at 2500rpm the voltage drops to normal 0.2-0.8 range - ie mixture under control, but as soon as it drops out of closed loop again the volts ramp up again to 0.9v.
Why is it running rich in open loop? where does mixture control come from in open loop? - cat code relay?
If I take the rubber caps off vacuum gauge stubs to allow air in it probably idles sweeter - slightly faster but sweeter, but in the past this would have caused engine to stutter and maybe stall - also, while the stub caps are off lamda voltage still up around 0.9v.

Any help welcome

Cheers...................Grizzly:beerjug:
 
If you got the fundamentals set right (valves & TBs synced and good sparkplugs) and provided the Lambda sensor and CCP setting is allright but still uneven running - re-tighten all the snappers around the TB intakes to air-box, or check if yer intakes are airtight - spraying some WD around rubber parts should give you a clue if it sucks it in and smokes it out or not. The rubber quality can be very poor and cracky (leaky) on some older BMWs and can create some unevenness over wide RPMs.

On higher mileage bikes replacing the throttle cables and throughoutly re-syncing usually makes that near-perfect (in rather agricultural boxer-terms of course) difference in smoothness over wide RPMs that couldn't be achived otherwise.
 
Have you changed the engine oil recently? If you're doing mainly short journeys, it's surprising how much fuel ends up diluting the oil - which affects slow running mixture more than you'd think. If your answer is yes to the above, then I reckon your lambda sensor is just getting sluggish - again quite common. If you read the Bosch technical data, the sensor is regarded as a 'service replacement' item in any case.
 
It could be a faulty temperature sensor.

A good lambda sensor should give one full oscillation in just over a second. Best seen with a scope. 172k and 13years is a high life for a lambda sensor.
 
I'm sure the temp sensor is fine - monitoring on laptop shows temp climbing fine, was up to 105 deg yesterday:eek:.
I think I now understand open/closed loop operation better now:eek. Originally I thought it went into closed loop a lot of the time, once warm, but it seems conditions have to be just right for it to switch. Uncle Dicks post made me re-check things and I then managed to get it to switch into closed loop - and when in closed the lambda is operating as you would expect - shows clearly on the GS-911 "scope" on the laptop.
I now suspect the reason it seems a little "fussy" getting the conditions spot on for closed loop may be a bit of wear in the LH thottle body, and although the TPS nominal setting is spot on, it is easy to get fluctuations on throttle angle read out by rocking throttle shaft -so the same thing is possibly happening when running due to inlet pulsations?
So, I think I'll have a look at a throttle re-bush when I get a chance. As I said at the beginning of this thread, the bike is running really nice (as usual) but I'm just trying to give it a thorough check over and analysis in prep for a biggish trip later in the year.

After listening to Uncle Dick and others I realised I wasn't fully understanding how open/closed/lambda should be working:rob - but while looking for info I found this webpage, which I thought explained things fairly well??? :-

http://www.bikeboy.org/open_closed_loop_efi.html

Cheers............................Grizzly:beerjug:
 
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