Air/Fuel and Vacuum Gauge Readings

[RacerX-21]

My Vacuum reading at idle is between 20-25 HG.

My Air/Fuel Gauge has some interesting readings: From 0 to 4000 RPM the stock computer is constantly adjusting, and bouncing between Lean and Max STOICH near the rich side (.050v to .800v). The second it gets to 4000, (even if the throttle isn’t wide open) the gauge stabilizes around .700v STOICH.

 

[true]

Originally posted by NSXEE:
My Vacuum reading at idle is between 20-25 HG.

My Air/Fuel Gauge has some interesting readings: From 0 to 4000 RPM the stock computer is constantly adjusting, and bouncing between Lean and Max STOICH near the rich side (.050v to .800v). The second it gets to 4000, (even if the throttle isn’t wide open) the gauge stabilizes around .700v STOICH.

Look in the manual for acceptable vacuum specs.

That A/F gauge you have is doing exactly what it's supposed to. The factory o2 sensor has a range of 1volt. It's basically on/off; or rich/lean. These narrowband o2 sensors are switching type. The ECU in closed loop just swings back and forth rich/lean doing whatever it needs to do (adjusting fuel delivery etc..) to keep the A/F at stoich or ~14.7:1. (mostly for emmisions purposes and good gas milage) Under ~3500RPM and less then ~25% is generally closed loop. Your gauge looks like nightrider until you hit open loop where it and reads the preprogrammed ecu tables and doesn't even listen to the o2 at all. You can't tune with a narrowband o2/gauge. The only thing it MAY be able to tell you is if it's running either rich OR lean at WOT....but of course not be how much either way. Very dangerous. I woulnd't trust it any way you look at it.


[This message has been edited by true (edited 08 October 2002).]

 

[RacerX-21]

Originally posted by true:
Look in the manual for acceptable vacuum specs.

That A/F gauge you have is doing exactly what it's supposed to. The factory o2 sensor has a range of 1volt. It's basically on/off; or rich/lean. These narrowband o2 sensors are switching type. The ECU in closed loop just swings back and forth rich/lean doing whatever it needs to do (adjusting fuel delivery etc..) to keep the A/F at stoich or ~14.7:1. (mostly for emmisions purposes and good gas milage) Under ~3500RPM and less then ~25% is generally closed loop. Your gauge looks like nightrider until you hit open loop where it and reads the preprogrammed ecu tables and doesn't even listen to the o2 at all. You can't tune with a narrowband o2/gauge. The only thing it MAY be able to tell you is if it's running either rich OR lean at WOT....but of course not be how much either way. Very dangerous. I woulnd't trust it any way you look at it.


[This message has been edited by true (edited 08 October 2002).]

I’m not sure what your saying
I’m only hooked to the output of the 02 sensor, (reading voltage) not the ECU.

The way I figure it, I’m getting the true Air/Fuel reading.

Is this wrong?

 

[true]

Originally posted by NSXEE:
I’m not sure what your saying
I’m only hooked to the output of the 02 sensor, (reading voltage) not the ECU.

The way I figure it, I’m getting the true Air/Fuel reading.

Is this wrong?

Hi Rob, I'm assuming you did not unplug your factory o2 sensors, and just tapped the signal. Even if you have added a seperate narrowband o2 sensor to a bung on your pipe specifically for the gauge, you still have the factory o2 sensors connected?

You are indeed reading voltage, from the sensor..the o2 sensor feeds that voltage to the ECU. Based on that voltage the ECU decides if it is rich or lean and makes a fuel injection adjustment. The cycle continues as long as it is in closed loop. A stock o2 sensor is accurate only at 14.7:1 a/f which is considered stoich. (14.7 particles of air to one particle of fuel). So the bottom line is that your gauge is seeing the same voltage the ECU is seeing...and the way the ECU handles closed loop operation is that switching or hunting you see on your gauge's LED.

For an example I'll use 0.00v to 0.50v is lean, and .50v to 1.00 is rich. I don't remember what the real voltage corresponding values are off the top.

o2 sensor -> comes .34v to ecu -> ecu decides lean ->bigger shot of fuel

Next cycle

o2 -> comes .78v to ecu -> ecu decides rich -> less fuel


and so on...

The constant switching is what you are observing on your gauge. Hope this helps/makes sense.. :\

[This message has been edited by true (edited 08 October 2002).]

 

[RacerX-21]

Yes it makes sense, and I can’t argue that a higher quality sensor and gauge wouldn’t be better for tuning. With better quality, comes higher cost. For now I will get the accurate readings from the dyno I go to.

I do feel that the meter I have gives some value. Bear with me… I installed EGT’s on my race engine to help with the tuning. My piers said that by the time I read a high temp, it would be too late. I went to the World Finals a few days early to test, on the second day I did a run just to get a base, incase temperature or barometer changed some of my results. My EGT’s were pegged, and they got there in a hurry. It turned out that my ignition lost an internal ground, so it defaulted to a generic timing and detonated. With out that gauge, I would have seized a piston, and definitely wouldn’t have won that year.

I am now partial to get as much information as I can afford. $33 Insurance.

Thanks for the info

Rob


Where is Wayne?

Born In Chicago, riesed in Evanston, led to Georgia.

 

[RacerX-21]

Is you NSX turbo charged?

 

[true]

Originally posted by NSXEE:
Is you NSX turbo charged?

I don't have an NSX.

I have a turbo honda/acura...same thing. Wayne is about 30 miles west of the city....st.charles area.