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Bigle

Altitude vs Air Fuel question - open loop

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Bigle

I am trying to verify my theory that the fz07 doesn't account for altitude in its air fuel mixture. I know at cruising it monitors the O2 sensor and adjusts, but for the rest of the time I believe it runs strictly off air temp, throttle position and rpm. 

I care about this because I live in Calgary at 3600ft so there's less air pressure. But I have a full akrapovic exhaust which would typically make me run lean. My theory is that being at high altitude reduces my air flow to help balance the exhaust and maintain a not so bad overall air fuel ratio. This should be a sound theory unless the bike has a barometric pressure sensor it uses all the time. Thoughts? 

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topazsparrow

I'd have to check, but most FI engines run a MAP sensor as well (manifold absolute pressure / Mass air pressure), so it should account for pressure changes.

 

If you want to enrich it a bit you can restrict your intake. A tune is better though :P

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firstyammerha

I believe the O2 sensor is on continuously from start up(cold) to warmed up running and believe it adjusts the fuel mixture regardless of altitude. The ECU uses inputs from the TPS,02 sensor and other sensors to keep the air/fuel mix in the optimum ratio. Correct me if I'm wrong.   

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Bigle
46 minutes ago, topazsparrow said:

I'd have to check, but most FI engines run a MAP sensor as well (manifold absolute pressure / Mass air pressure), so it should account for pressure changes.

 

If you want to enrich it a bit you can restrict your intake. A tune is better though :P

Yea if there is indeed a map sensor then I'm certainly lean with the exhaust. Good to know it is a plausible common thing to have. If that is the case I'm likely lean and ill buy a fuel controller, wouldn't want to restrict the stock intake any further haha. 

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mt7fan

I drive every now and then in the Austrian alps almost to 3000 meters. I notice no difference in torque with stock bike.

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Bigle
45 minutes ago, firstyammerha said:

I believe the O2 sensor is on continuously from start up(cold) to warmed up running and believe it adjusts the fuel mixture regardless of altitude. The ECU uses inputs from the TPS,02 sensor and other sensors to keep the air/fuel mix in the optimum ratio. Correct me if I'm wrong.   

I do believe that is wrong. It only uses the O2 sensor in certain situations like cruising. It can't react quick enough otherwise. That's why you can't heavily modify airflow without adjusting tune as it won't know most the time. On a car though or some bikes they use the O2 sensor etc all the time 

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firstyammerha

so our ECU is not as sophisticated as a cars. Wouldn't surprise me.

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cyow5

Lots of bad info here. 

The FZ only uses the MAP sensor occasionally, mostly low load, and never more than something like 30% weighting factor. I don't have the map in front of me, but its floating around here somewhere. That means most of the time the base fuelling is from the throttle angle and rpm only. 

The O2 sensor is narrow band, so it is only functional when the desired AFR is stoich, in other words, light load. 

Wideband O2 sensors are astonishingly fast and can be used 100% of the time except fuel cuts and highly transient events like shifting where it doesn't matter as much anyways. 

You will run leaner at altitude, for sure. Is it important? Depends on how rich the base fuelling is and all that. The self-tuning options out there simply add a wideband and let it adapt, so you are probably a perfect candidate for that

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topazsparrow
22 minutes ago, firstyammerha said:

so our ECU is not as sophisticated as a cars. Wouldn't surprise me.

Most cars do this too.

 

Closed loop is just for fuel savings and just tries to run lean - since at low load and lower RPM being lean wont cause damage.

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firstyammerha

closed loop is an a/f enrichment function as I recall used for cold start and running.

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Bigle
Posted (edited)
19 minutes ago, cyow5 said:

Lots of bad info here. 

The FZ only uses the MAP sensor occasionally, mostly low load, and never more than something like 30% weighting factor. I don't have the map in front of me, but its floating around here somewhere. That means most of the time the base fuelling is from the throttle angle and rpm only. 

The O2 sensor is narrow band, so it is only functional when the desired AFR is stoich, in other words, light load. 

Wideband O2 sensors are astonishingly fast and can be used 100% of the time except fuel cuts and highly transient events like shifting where it doesn't matter as much anyways. 

You will run leaner at altitude, for sure. Is it important? Depends on how rich the base fuelling is and all that. The self-tuning options out there simply add a wideband and let it adapt, so you are probably a perfect candidate for that

Thanks for the hard info thats exactly what I wanted to know. Except I think you're backwards when you say it will run leaner at altitude.. Shouldn't less air (at altitude), with the same amount of fuel (assuming its not adjusting most of the time) result in a richer mixture? Then the question becomes how much richer is it at my altitude, and does that offset my added air from the exhaust to end up okay overall. From my mental math, my altitude would have roughly 10% less air then sea level. making it 10% richer than stock in situations except low load where it is accounting for it (assuming it was tuned to be correct at sea level which I'm not sure). Then, from dyno graphs, I would estimate a full exhaust provides roughly 5% more air at most. In which case I am actually rich not lean (again depending on what altitude they setup the stock tune at, which is foresure lower altitude than here anyway). Can you confirm you were mistaken about the leaner at altitude thing? Thanks again for the response. 

Edited by Bigle

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cyow5
4 minutes ago, Bigle said:

Thanks for the hard info thats exactly what I wanted to know. Except I think you're backwards when you say it will run leaner at altitude.. Shouldn't less air (at altitude), with the same amount of fuel (assuming its not adjusting most of the time) result in a richer mixture? Then the question becomes how much richer is it at my altitude, and does that offset my added air from the exhaust to end up okay overall. From my mental math, my altitude would have roughly 10% less air then sea level. making it 10% richer than stock in situations except low load where it is accounting for it (assuming it was tuned to be correct at sea level which I'm not sure). Then, from dyno graphs, I would estimate a full exhaust provides roughly 5% more air at most. In which case I am actually rich not lean. Can you confirm you were mistaken about the leaner at altitude thing? Thanks again for the response. 

Good catch! Yes, richer at altitude. Blame it on the new baby that doesn't sleep, haha

And yeah, you can pretty safely assume a linear relationship for this case so 10% less air is 10% less rich. Probably less power, but probably not quite 10%, but that really depends again on how rich it was to start with since richer adds power to a point and then reduces it. 

 

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Bigle
3 minutes ago, cyow5 said:

Good catch! Yes, richer at altitude. Blame it on the new baby that doesn't sleep, haha

And yeah, you can pretty safely assume a linear relationship for this case so 10% less air is 10% less rich. Probably less power, but probably not quite 10%, but that really depends again on how rich it was to start with since richer adds power to a point and then reduces it. 

 

Haha you must be tired you did it again, 10% less air is 10% more rich 😛. Well assuming the map sensor indeed only adjusts under low load, I think I'll assume I'm not leaning out under accelerations due to my exhaust. But the final verdict would still be knowing the altitude the bikes are tuned at, and verifying the map sensor peaces out when I get on the throttle. 

I could always check what its actually doing with a Wideband too, if the opportunity arises. 

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firstyammerha

I think I got my open/closed loop function reversed. That's what I get for relying on memory.

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Bigle
9 minutes ago, firstyammerha said:

I think I got my open/closed loop function reversed. That's what I get for relying on memory.

I think you had it right, closed loop means adjusting to sensors etc. I don't get it though that should be what they label as open loop. I just remember its backwards to what you'd think it is. 

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