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SHIFT_FASTER
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Discussion Starter #1
So I did a test, and apparently the Murano never enters closed loop mode above 4000 RPMs, regardless of whether you mash the pedal (which definately leaves closed loop mode) or put it in S or L and cruise at a speed high enough to get the RPMs above 4000.

What I'm wondering is, how are the fuel maps adjusted for RPMs above 4000?

Normally, you have a fuel map that is probably 3 dimensional, with the 3 dimensions being airflow (from the MAF sensor), load (calculated somehow) and RPM. When the engine is running in closed loop mode (using feedback from the oxygen sensors), it will adjust these fuel tables with both a short term adjustment and a long term adjustment (referred to as short term and long term fuel trim), in order to achieve the desired air-fuel ratio for those conditions.

But if the engine never enters closed loop mode above 4000 RPMs, do these tables always just use the factory programmed values? If this is the case, it would result in extreme inefficiency in some cases, and possible engine damage if enough "airflow mods" were done to result in an overly lean condition.

The only solution I can think of is to use extrapolation from the under 4000 RPM tables. Anyone have any other ideas?
 

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My MO's faster than yours
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Tyler_Canada said:
So I did a test, and apparently the Murano never enters closed loop mode above 4000 RPMs, regardless of whether you mash the pedal (which definately leaves closed loop mode) or put it in S or L and cruise at a speed high enough to get the RPMs above 4000.

What I'm wondering is, how are the fuel maps adjusted for RPMs above 4000?

Normally, you have a fuel map that is probably 3 dimensional, with the 3 dimensions being airflow (from the MAF sensor), load (calculated somehow) and RPM. When the engine is running in closed loop mode (using feedback from the oxygen sensors), it will adjust these fuel tables with both a short term adjustment and a long term adjustment (referred to as short term and long term fuel trim), in order to achieve the desired air-fuel ratio for those conditions.

But if the engine never enters closed loop mode above 4000 RPMs, do these tables always just use the factory programmed values? If this is the case, it would result in extreme inefficiency in some cases, and possible engine damage if enough "airflow mods" were done to result in an overly lean condition.

The only solution I can think of is to use extrapolation from the under 4000 RPM tables. Anyone have any other ideas?

closed loop? mind explaining further on this? please:)
 

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Open loop = relies on a preset map without using O2 sensor data, usually runs in inefficient rich condition

Closed loop = uses O2 sensor data to optimize air/fuel mixture, maximizes fuel economy and reduces emissions

You want to be running in closed loop as much as possible, or you'll be getting 12mpg.
 

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My MO's faster than yours
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Tyler_Canada said:
So I did a test, and apparently the Murano never enters closed loop mode above 4000 RPMs, regardless of whether you mash the pedal (which definately leaves closed loop mode) or put it in S or L and cruise at a speed high enough to get the RPMs above 4000.

What I'm wondering is, how are the fuel maps adjusted for RPMs above 4000?

Normally, you have a fuel map that is probably 3 dimensional, with the 3 dimensions being airflow (from the MAF sensor), load (calculated somehow) and RPM. When the engine is running in closed loop mode (using feedback from the oxygen sensors), it will adjust these fuel tables with both a short term adjustment and a long term adjustment (referred to as short term and long term fuel trim), in order to achieve the desired air-fuel ratio for those conditions.

But if the engine never enters closed loop mode above 4000 RPMs, do these tables always just use the factory programmed values? If this is the case, it would result in extreme inefficiency in some cases, and possible engine damage if enough "airflow mods" were done to result in an overly lean condition.

The only solution I can think of is to use extrapolation from the under 4000 RPM tables. Anyone have any other ideas?
What kind of test did you run to figure this out? Do you think its like this just for the MO? or other VQ equiped cars?
 

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I am going to guess Tyler just looked it up in the FSM.
 

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SHIFT_FASTER
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Discussion Starter #6
Nope, didn't look it up. You can check O2 sensor operation using one of those Key and Gas Pedal tricks. If you watch the light in closed loop mode, it blinks on and off, indicating a continuous switch between rich and lean. This is what you see with any type of O2 sensor that's not wide-band (continuous switch between rich and lean). When you go into open loop mode, the light stays either on or off, as the computer has started to ignore the oxygen sensor. As Eric states, when in open loop, you are usually running rich, and therefor off the scale for the oxygen sensor, so the readings are not valid (which is why it's ignored).

I don't know whether it would be all VQ vehicles, or just Muranos.
 

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Not knowing much about this but wouldn't you want it to be open above 4000 RPMs for better engine cooling due to the additional fuel? Why is it being open above 4000 a surprise? Do other cars close?
 

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SHIFT_FASTER
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Discussion Starter #8
Gonzo said:
Not knowing much about this but wouldn't you want it to be open above 4000 RPMs for better engine cooling due to the additional fuel? Why is it being open above 4000 a surprise? Do other cars close?
That's right, but I'm just wondering how it knows how much fuel to put it. Say it just uses preset values that aren't updated. If you added enough mods, you would be adding more air, and would then end up running too hot at higher RPMs, because the computer doesn't know to add more fuel.
 
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