Legitimacy of AFR gauges

[TomoHawk]

5 hours ago, jonbill said:

In theory...

That theory is well known, but presumes you have an engine that is working 100% perfectly and you have a 100% perfect combustion.

Edited November 24, 2018 by TomoHawk

[jonbill]

1 hour ago, Patcon said:

But a good first post!

Thanks.

48 minutes ago, TomoHawk said:

That theory presumes you have an engine that is working 100% perfectly and you have a 100% perfect combustion.

Funnily enough, it doesn't - it mainly depends on the chemistry of the fuel and air mixture which hasn't changed for a very long time.

I'm sure there are conditions in which the accuracy is compromised significantly, but it's not within the normal degradation of an engine say in the first few 100k miles of it's life.  That's why many of the spark ignition cars of the last 20 odd years are still on the road passing their emissions tests using this technology to regulate their fueling.

[TomoHawk]

They also have more than just the one oxygen sensor, in a few places, and modern electronic or digital engine controllers that make up for sensor degradation and other compromises.  I see no reason why you can rely on only one oxygen sensor. to get an overall and precise air-fuel mixture determination.

Edited November 24, 2018 by TomoHawk

[jonbill]

I have a 20 year old mr2 with 3 sensors and 20 year old modern engine management electronics. The first sensor measures the output of cylinders 1 & 4, the second measures the output of cylinders 2 & 3 and the last measures the aggregate after the catalytic converter to judge whether the cat is working or not.
I believe this is representative of multisensor setups. Each sensor is trusted to measure its bit independently.
Sensors of course do fail.
The management system strategy for this is to constantly cycle mixture up and down a bit to check if the sensor reports it. If it doesn't it reports a fault.

There's no reason to not believe a single sensor and controller and gauge will report reasonably accurately the average AFR of the combustion chambers it's monitoring.

[TomoHawk]

You are right, about the use of the multi-sensor setup, and how it's all used to get an "average"  or overall  fuel mix that works reasonably well, and it agrees with my opinion that just the one sensor can't do the whole job.  It makes you wonder why so people put their whole confidence in just the one sensor, how there's a whole aftermarket industry that makes a LOT of profit on it.

Edited November 24, 2018 by TomoHawk

[Patcon]

36 minutes ago, TomoHawk said:

You are right, about the use of the multi-sensor setup, and how it's all used to get an "average"  or overall  fuel mix that works reasonably well, and it agrees with my opinion that just the one sensor can't do the whole job.  It makes you wonder why so people put their whole confidence in just the one sensor, how there's a whole aftermarket industry that makes a LOT of profit on it.

Actually the ECU relies on each O2 sensor independently. They are used as much to determine faults and OBD codes as real time fueling. They are also used to cross check each other. Not so much for accuracy but for function. I have found that when it an O2 sensor fails it's dead, not out of spec. So if my wideband O2 fails which it has in the past I get no AFR readings. 

[madkaw]

I don’t get this thread. Why are we arguing the science behind a device that is so widely accepted in the industry. It works - use your time for something else IMHO

[zKars]

2 hours ago, madkaw said:

I don’t get this thread. Why are we arguing the science behind a device that is so widely accepted in the industry. It works - use your time for something else IMHO

When do we get to discuss if the coolant temp sensors are correct or not? AFM? Thermostat?

Oh right, we should do something else now....

Edited November 25, 2018 by zKars

[TomoHawk]

Because using an oxygen sensor as the sole sensor for the Air-fuel ratio is like measuring tyre pressure using the temperature of the rubber tyre.

[madkaw]

It always bothered me that there  isn’t an indicator on the dash to verify I am in 3rd gear and not 5th. Just because I push the shifter further over - how do I really know that I am in 5th and not 3rd? Just because I follow the pattern on that stupid little knob doesn’t mean I have actually changed anything

[grannyknot]

10 hours ago, madkaw said:

Just because I push the shifter further over - how do I really know that I am in 5th and not 3rd?

The engineers included a built in audible warning signal that you are in 3rd when you should be in 5th,  it sounds like a high pitched turbine combined with breaking metal, very distinctive sound.

[Captain Obvious]

Haha!!      From the Zcon thread:

On ‎11‎/‎18‎/‎2018 at 2:14 PM, Mark Maras said:

As the smile starts to spread across my face I shift into 3rd and then 4th gear and put the gas pedal to the floor just to keep up with Bill and Jai. Soon I think, OK, time for 5th gear. Slip it into neutral over to the right and up. Goes in easily, I let out the clutch and immediately realize that it was in 3rd and also realize this is a 4 speed.

 

Edited November 25, 2018 by Captain Obvious