General Category > Engine related issues
Lambda/O2 sensor/probe stuck at 870mv
javadude:
Until yesterday I’d only ever used the mobile version of the software to check for error codes and other readings I understood.
Yesterday, I plugged in my laptop and clicked around the PC version of the software to see what it more could do. One of the things I did was to look at the Lambda voltage, which was high at c. 870mv and well above the green band – i.e. fuelling running rich.
I went away and did some research to learn that the Lambda graph should really be jumping around, whereas mine was almost flat at a fairly constant 870mv. I also learnt that the engine should be up to temperature before taking any meaningful readings.
So today I connected my laptop and started the GS-911 data logging (spreadsheet enclosed). I pulled the fast idle trigger into its first position – the BMW Repair Manual refers to this as ‘starting-speed increase’ - started the engine from cold and allowed the engine to warm up. When it reached operating temperature, around 80C, I turned the fast idle off whereupon the idle speed dropped from about 2,2000 RPM to around 1,100 RPM.
I expected the Lambda voltage to start jumping around but it remained stuck at about 870mv.
Even as the engine temperature continued to increase it remained stuck at about 870mv. I switched the engine off and went back inside to take a look at the data log.
The first thing I noticed, is that all the way through ‘Lambda closed-loop control’ remains at 0 (zero) – i.e. open-loop. My understanding is that it should switch to closed-loop when the engine gets to operating temperature.
The second thing I noticed, is that ‘Idle switch’ remains at 1 (one). So I went back to the start of the log and can see that it starts at 0 (zero), and changes to 1 (one) before the engine starts up. This tells me that it is switching on but not switching off again. At this point in time my theory is that this is forcing the ECU to remain in open-loop.
I’ve checked the BMW Repair Manual and wiring diagrams for my bike, but I can’t see a physical ‘idle switch’ anywhere.
I could have missed something of course, but my question is this: How does the ECU know when the ‘idle switch’ is on or off?
Thanks in advance for your help!
Motronic MA2.4
Motorcycle Variant: R1100 S ECE-Kat
Part No.: 1342982
Bosch Part Number: 0261204709
ECU Software Number: 1037359252
ECU coding variant: 0
ECU program version: 43010300
Manufacturer: Bosch
HWOE No.: 42375823
Idle Actuator: No
Emissions control type: Lambda
Jughead:
You may well find that the TPS (Throttle Position Sensor) needs to be adjusted correctly. I did a write-up some time ago on how to set up the TPS and throttle bodies correctly. Will try to find it and post it here for you.
Jughead:
Here you go.
Adjust valve clearances.
Starting with the left throttle body, remove and clean the BBS using brake cleaner or whatever you prefer.
Remove the rubber cap from the vacuum port, remove the throttle body from the intake manifold, clean TB with brake cleaner and blow dry with compressed air.
Replace the BBS, applying a dab of rubber grease to the o-ring.
Turn the BBS in all the way and then back it out 1.5 turns.
Loosen the locknut on the throttle stop screw on the LHS throttle body and back the screw out so that the butterfly closes completely.
Make sure there is enough free play on the cable.
Refit the throttle body and plug in the TPS
With a multimeter connected to pins 1 and 4 of the TPS connector, turn on the ignition and adjust the TPS to give you a reading of 0.25V.
Lock the TPS in that position and do not touch it again.
Now adjust the throttle stop screw to give a reading of 0.36V. Lock it in place using the locknut.
The LHS throttle body is now set up correctly.
Repeat the cleaning process on the RHS throttle body, and also adjust the BBS to 1.5 turns out once clean.
Start the motor and adjust the balance at idle using the throttle lock screw on the RHS only, NOT the BBS.
Once balanced, both throttle bodies will now be working in sync at idle.
Now bring the rpm up to around 3500 - 4000 RPM and adjust the cables to balance.
If you check your idle switch now, it will most likely be off.
Hope this helps.
javadude:
--- Quote from: Jughead on June 09, 2019, 08:44:04 AM ---You may well find that the TPS (Throttle Position Sensor) needs to be adjusted correctly.
--- End quote ---
Thanks for the suggestion. I don't think that the TPS adjustment is the problem, as it's nicely in the green zone according to GS-911 readings.
I'll post a couple of graphs from the log. Measures other than 'Idle switch' show that the ECU registers the fast idle being switched off.
javadude:
https://drive.google.com/open?id=1hr4TgtIoog1-rSt-nE54yJtjDMeKZiC5
In the top graph, about 2/3 along, the 'Ignition angle' drops as does the 'Throttle position (TPS)' when the 'fast idle' is switched off.
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