While we're on the subject, what exactly do the "AFR Target" tables do in $EE? We only have narrowband O2 sensors, so it can't be querying a wideband for precise AFRs. So what are these tables referencing as AFR?
While we're on the subject, what exactly do the "AFR Target" tables do in $EE? We only have narrowband O2 sensors, so it can't be querying a wideband for precise AFRs. So what are these tables referencing as AFR?
1990 Corvette (Manual)
1994 Corvette (Automatic)
1995 Corvette (Manual)
Not EE specific, but an open loop table is used when open loop. While open loop, the loop to the O2 sensor is not used, such as warm up, PE, Decel cut off, or O2 error. Some tunes have the table enabled during closed loop for sort of a lean cuise, anytime anything other than stoich is targeted, you are open loop
No need to re-invent the wheel. But we can make it better
1990 Corvette (Manual)
1994 Corvette (Automatic)
1995 Corvette (Manual)
To be more specific, fueling is based on airflow, how much air is going in the engine.
Knowing how much air is going in, the pcm can calculate how much fuel is needed.
The ratio is how many part of air to one part fuel
AFR
Air to Fuel Ratio
If we we are taking in so many lbs of air, we need so many lbs of fuel to mix the ratio.
Does that make sense?
No need to re-invent the wheel. But we can make it better
most ecms work like this
1. you have an airflow measurement, either with a MAF or speed density (a volumetric efficiency map, in other words a chart that says 'in this condition the engine flows this much air')
2. you have the fuel flow metrics, that end up calculating something like 'if you open the injector for this long, this much fuel comes out'
3. you then try to hit your AFR target vs airflow vs injector metrics to figure out how much fuel to inject
this is both in open loop and closed loop.
there are auxiliary calculations like closed loop trims, transitional fuel needs like accel enrichment, and some other small calculations and constants, but those modify things in the above three steps. without step three, you aren't going anywhere.
in other words, without step three, how would you know that you don't inject one part air for one part fuel?
Good in depth simple explanation stevo. I hope he understands.
I think there are a lot of people who think fuel control is from O2 sensor only.
Last edited by ralmo94; 04-06-2022 at 05:16 AM.
No need to re-invent the wheel. But we can make it better
I don't think fuel control is from O2 sensors only; I'm just used to a completely different computer environment since I primarily worked with Japanese cars instead of American ones. Or rather, my Corvettes are the first American PCMs I've mucked with. In the Japanese world you have actual "fuel tables" that are set to deliver a certain amount of fuel for a specific load cell (RPM vs airflow). There is no "AFR Target" setting because the AFR will depend on how much fuel is put into any given load cell in the fuel map.
Now that steveo has explained that these PCMs don't use "fuel tables" in the traditional sense but rather have calibrations for airflow measurement, it makes a lot more sense. Thanks to both of you!
1990 Corvette (Manual)
1994 Corvette (Automatic)
1995 Corvette (Manual)
I'm glad you understand what you are adjusting, it's hard to do something you don't understand.
Just to be clear I didn't mean to insult your intelligence, and I'm sorry if you felt that way, I haven't seen a Japanese calibration that was setup the way you described, I can imagine I would e confused if I looked at one.
No need to re-invent the wheel. But we can make it better
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