800GS - 30% decrease in MPG and no fault codes

[alex_rsa]

Hi all,

I am looking for some help before I throw more money in the wrong direction.

800GS starting running badly, poping and banging (more than normal) through the exhaust and the fuel consumption decreased by 30% (120 vs 170 miles per tank). If you go to WOT quickly the bike stumbles for a few seconds, emits some black (fuel) smoke before slowly starting to accelerate. If you roll on the throttle slowly it works OK.

The consumption is consistent over the last 10 tanks and the on-board computer cannot deal with the fuel usuage as that shows 20+ miles range and it will run dry. The computer is also showing the fuel consumption as 4.4l/100km although is is close to double that.

The issue happened suddenly (no recent service or any other changes). GS911 is not listing any error codes.

The problem happens from cold so it cannot be the Lamda (this only starts working at 80c) although I did replace it in the forlorn hope that would solve the issue.

I also replaced both stick coils but this has not changed anything.

It is basically over-fueling from the moment it is started. What would cause constant overfuelling? What realtime value can I check?

Before I go buy a TPS, fuel pressure sensor or fuel pump has anyone any ideas?


thanks


Alex

[schuppi]

Hi Alex,
welcome to GS911 forum.

Sounds like you have to do some mechanical inspection, if there are no faults stored.

" starting running badly, poping and banging"
 > compression? spark plugs? wiring + connectors from stick coils, checking valve clearance.

If that's all good, check temperature sensor, heating circuit of lambda sensor.
That will be my first checks
And then, it would be helpful to send an Auto-Scan, even without any faults and maybe a log while idling.

[alex_rsa]

Thanks Schuppi,

The bike has always popped from the exhaust (it is aftermarket can) but it is much more pronouced and frequent. It only does it on after-run, the exhaust tip is now black and sooty from the rich running.

New spark plugs were the first things I tried, no difference.

The engine sensor for ambient temperature matches the real outside temperature and the Lamda was replaced but the Lamda does not get used until the water temp is 80C. The bike runs rough from cold start.

What values do you want to plot? I think you can have 6?

What occured to me yesterday is that the on-board computer fuel consumption is not matching reality. It says I am averaging 4.4 l/100 when i am closer to 8l/100. I assume this is because whatever is actually worng is causing un-metered fuel into the engine.

Both cyclinders appear to be affected as spraying carb cleaner down either throat causes the bike to stumble the same.

The only thing that could cause this (I think) would be excessive fuel pressure but surely the sensor on the fuel-rail will pick that up?

Thanks


Alex

[schuppi]

Hello Alex,

please log real-time values like
idling speed and throttle position
coolant temperature
Oxygen sensor signal
Oxygen sensor heating if possible, here will be the main fault > as you mentioned> Lamda does not get used until the water temp is 80C?
maybe you have to measure directly with a voltmeter. This heating runs quickly after start to ensure the fast function, regulation
of the lambda sensors. There must be a fast oscillation value between 0,2 to 0,8 V shortly after start the engine

Hope this will show you the right way

By the way, consumption will be calculated by the ECU without fuel flow volume