R1100GS Air Fuel Guage Reads Rich on Idle

JoePap

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I've recently fitted a wideband O2 gauge with a sensor that I can swap between the two downpipes. It gives a digital reading with 14.3 being perfect combustion. Low numbers are rich, high numbers are lean.
Overall the bike is running pretty well. The only issues are

1) Running rich on tickover - reading around 10 or slightly under on the Air Fuel gauge.
2) Tickover seems a bit high (Just under 1000 rpm)

The mileage is 35,000. Being an early bike it has the very simple fuel injection system with no lambda sensor.
I've done all the service items including

- Recent injector clean
- Valve clearances
- There's a little slack in the throttle cable so it's not opening the throttle bodies when the twist grip is shut off
- The "Choke" cable is working properly and not binding or part opening
- The throttle bodies are balanced
- To get the tickover down below 1000 rpm I've had to screw both big brass air screws fully home (See further comments below)
- Throttle position sensor set to give zero volts on the number 1 connector with closed throttle (To achieve this I had to rotate it anti-clockwise almost to the limit)
- Ive tried adjusting the C0 potentiometer. Measuring at the number 2 (middle) contact. I can vary the voltage from 0v to 4v with no noticeable affect. The bike was fully warmed up when I did this.
- As recommended by the manual and various info online, I've left the throttle stop screws alone

When cruising and on wide throttle openings, the bike pulls and rides very well. There's no surging. The air fuel gauge tells me the mixture is very good.
But when I leave the bike ticking over, the bike labours a bit. It smells and sounds like it's rich and the air fuel gauge confirms - reading around 10. Although tickover is nearly 1000 rpm it sometimes stalls.

If it was a carburettor bike, I’d open the air screws and adjust the throttle stops. But the instructions for the oil-heads say to leave the throttle stops well alone and to use the air screws to adjust tickover rather than idle mixture.

I'm tempted to look into re-mapping the ECU but only if everything else is adjusted properly.

I'd be interested any suggestions and any insight into the system including

- why the throttle stops should not be adjusted?
- Why the air screws are used to adjust tickover rather than idle mixture?
- How the CO potentiometer is supposed to work? Are higher voltages from it telling the ECU to add or reduce fuel?

Thanks.

Joe
 
What cat coding plug is in the bike? In the fuse box, looks like a relay, should either be beige, yellow or pink (or not there at all)

I am still trying to figure out how to adjust my AFR with the co-pot, as I also cant detect any difference when adjusting it. That's with the BEIGE co-pot installed. Im currently running with no coding plug as the bike runs best, but im using more fuel than with it installed. With the beige plug in, I get popping on the overrun and surging at low speed, but better fuel economy.

My bike is also an R1100GS with no o2 sensor.
 
Good point gog. My bike has no coding plug fitted.

My throttle stop screws have no paint on them. I don't know the history so I can't be sure they've not been altered by a previous owner.

Having refitted the vacuum gauges again and playing about with the large brass air-screws, I'm probably next going to make throttle stop adjustments. It seems the obvious thing to do but I wonder why everyone says don't??
 
Just think, if you didn't have an air/fuel gauge you'd be perfectly happy riding your bike without a care in the world. . The air screws have no effect on the fuel injectors or the amount of fuel injected. Same with the throttle stop screws. The throttle stop screws adjust the throttle butterfly's, that's why you don't touch them as it affects the flow on all throttle openings not just idle.
 
Regards last three posts.

The idle is lumpy and the exhaust smells rich. I wasn't happy riding it before. Especially when it stalls in traffic. The air fuel gauge is a diagnostic tool.

I'm guessing BMW didn't intend it to run rich on tickover and something's wrong.

Steptoe's post about closing the butterfly valves is a good one. I understand air will be reduced and (unlike a carb) fuel won't be directly affected (being supplied by the injector). I guess backing off the throttle stop will reduce idle speed but make the bike run even richer - not the desired result. I'll leave them. But I'm still stuck how to cure the rich idle problem.

Perhaps it's best just to leave things as they are, hoping I don't get arse-ended in traffic, kill my battery and or my starter motor. Maybe just not ride the bike in London.
 
Regards last three posts.

The idle is lumpy and the exhaust smells rich. I wasn't happy riding it before. Especially when it stalls in traffic. The air fuel gauge is a diagnostic tool.

I'm guessing BMW didn't intend it to run rich on tickover and something's wrong.

Steptoe's post about closing the butterfly valves is a good one. I understand air will be reduced and (unlike a carb) fuel won't be directly affected (being supplied by the injector). I guess backing off the throttle stop will reduce idle speed but make the bike run even richer - not the desired result. I'll leave them. But I'm still stuck how to cure the rich idle problem.

Perhaps it's best just to leave things as they are, hoping I don't get arse-ended in traffic, kill my battery and or my starter motor. Maybe just not ride the bike in London.

Ride the bike in London as far as Steptoe’s workshop
 
Maybe your Co pot is fecked if adjusting it makes no difference to the idle mixture.
 
Joe, I’ve used a wideband a lot and have a lot of afr data on the oilheads. Comments below in red.

I've recently fitted a wideband O2 gauge with a sensor that I can swap between the two downpipes don’t get it too close to the head. Leave a foot if you can. . It gives a digital reading with 14.3 being perfect combustion if by perfect you mean stoic, 14.3 is about the number for E10 fuel.. Low numbers are rich, high numbers are lean.
Overall the bike is running pretty well. The only issues are

1) Running rich on tickover - reading around 10 or slightly under on the Air Fuel gauge. your co pot is missing or misadjusted
2) Tickover seems a bit high (Just under 1000 rpm) tickover spec is 1200

The mileage is 35,000. Being an early bike it has the very simple fuel injection system with no lambda sensor.
I've done all the service items including

- Recent injector clean
- Valve clearances
- There's a little slack in the throttle cable so it's not opening the throttle bodies when the twist grip is shut off
- The "Choke" cable is working properly and not binding or part opening
- The throttle bodies are balanced
- To get the tickover down below 1000 rpm I've had to screw both big brass air screws fully home (See further comments below)
- Throttle position sensor set to give zero volts on the number 1 connector with closed throttle it should read 340 mV (To achieve this I had to rotate it anti-clockwise almost to the limit)
- Ive tried adjusting the C0 potentiometer. Measuring at the number 2 (middle) contact. I can vary the voltage from 0v to 4v with no noticeable affect. The bike was fully warmed up when I did this.
- As recommended by the manual and various info online, I've left the throttle stop screws alone since you had to bottom the bbs screws some has already moved them

When cruising and on wide throttle openings, the bike pulls and rides very well. There's no surging. The air fuel gauge tells me the mixture is very good.
But when I leave the bike ticking over, the bike labours a bit. It smells and sounds like it's rich and the air fuel gauge confirms - reading around 10. Although tickover is nearly 1000 rpm it sometimes stalls.

If it was a carburettor bike, I’d open the air screws and adjust the throttle stops. But the instructions for the oil-heads say to leave the throttle stops well alone and to use the air screws to adjust tickover rather than idle mixture.

I'm tempted to look into re-mapping the ECU but only if everything else is adjusted properly. Your bbs, co pot, TPS, throttle stops are all misadjusted. Do a proper alignment first

I'd be interested any suggestions and any insight into the system including

- why the throttle stops should not be adjusted?
- Why the air screws are used to adjust tickover rather than idle mixture?
- How the CO potentiometer is supposed to work? Are higher voltages from it telling the ECU to add or reduce fuel?

Thanks.

Joe
 
Hi Roger.
Your advice was very useful.
The bike's running really well now. Rich tickover cured. No-longer smells bad on tickover. Smooth idle and no stalling.
As you advised, I set the TPS to that voltage.
I've now learned that CO2 potentiometer adjustment only affects the mixture when the ECU gets exactly the right TPS voltage with the throttle shut. (Also dependent on full engine temp and tickover rpm. The ECU runs in "Tickover mode", which actives the CO2 potentiometer.
So it's a good confirmation of a correctly set TPS if the CO2 pot can be used to adjust idle mixture.
Now that the TPS is re-set, The CO2 potentiometer works fine so I was able to set the idle mixture just right.
I refitted the vacuum gauges and the throttle bodies are perfectly balanced. They're in perfect sync in all riding conditions. The bike riding better than ever.
Thanks for all the information you provided.
Happy trails.
Joe
 
.
I refitted the vacuum gauges and the throttle bodies are perfectly balanced. They're in perfect sync in all riding conditions. The bike riding better than ever.

Good job you didn't start messing about with the throttle stop screws. :D
 


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