Why does O2 read zero while coasting?

[BJM]

Whenever I coast in the car the scanmaster shows low to zero readings on the O2. I know this is normal but what I don't understand is why? The BLMs in those situations is usually low on may car as well ~105-110. Since the computer is still in control why isn't the computer driving in fuel until stoichiometric conditions are obtained? When does the computer use fuel cutoff?

 

[tminer]

It cuts off fuel during decelleration. I don't know the parameters. Those BLM's are whatever is in the current cell, based on rpm and MAF. They are not being used or updated during DFCO.

The output curve of a narrow band O2 is like the profile of a seaside cliff. The water level is 0v and lean, then a sharp rise in the close vicinity of stoich (hence "narrow" band), and then the land is max voltage and rich.

Tom

 

[bruce]

Originally posted by BJM
Whenever I coast in the car the scanmaster shows low to zero readings on the O2. I know this is normal but what I don't understand is why? The BLMs in those situations is usually low on may car as well ~105-110. Since the computer is still in control why isn't the computer driving in fuel until stoichiometric conditions are obtained? When does the computer use fuel cutoff?

There's no reason to maintain the ability to make power when coasting, and to increase the MPG, and reduce emissions they have what's called DFCO. DFCO means Decleration Fuel Cut Off.

So at low TPS voltages at higher then idle rpm, above a min temp., and above a certain road speed the injectors are turned off. The parameters are adjustable in the chip.

Some turn the DFCO off, and use it as a anti-lag devise. Downside is that when drag racing it tends to make the engine stall after the burnout, unless you play with the IAC stuff.

 

[BJM]

bruce


Do you know what the parameters typically are? The O2 values drop way down or even zero at quite slow speeds in my car, 35 mph coasting for example.

If the injectors are actually off it sure sounds like the engine is still running.

 

[bruce]

Originally posted by BJM

Do you know what the parameters typically are? The O2 values drop way down or even zero at quite slow speeds in my car, 35 mph coasting for example.

If the injectors are actually off it sure sounds like the engine is still running.

If the O2 sensor is reading 0, then there is no power being made. If it's reading 0, then there is no burnt fumes in the pipe.
It's still spinning, yes, but without fuel, it's just not making any power.

If you poke aroung the GNType site there is an excel spreadsheet that has all the information, and original values, for all the calibration data. You can read thru it and see the DFCO, AE, PE, all the settings that can be edited.