A/F gauge jumps all over the place...

[BoostedBird]

I am looking to purchase a 98 TSi AWD and I test drove it last night. It has an A/F gauge in the A pillar and I was watching it while we were driving and idling. The lights just seemed to bounce back and forth. Is this how it is supposed to be?

 

[talonted_one]

yes

 

[logic]

Yes, this is perfectly normal. If you get a chance to run the car at WOT, you'll see that it (hopefully) sits stationary in the green the whole time.

 

[BoostedBird]

Cool. Thanks guys! Just thought maybe it was "searching", like maybe it needed to be tuned. But I guess not.

 

[Isotta91]

a/f gauges are so useless on our cars. i don't even pay attention to mine cause i know its wrong. it's just a practical gauge to put on with a boost gauge.

 

[4G92-T]

Are these aftermarekt A/F gauge any good at all?

I have an APEXi A/F gauge (the model that incorporates a Turbo timer). I recently went for tuning with a MOTEC wide band 02 sensor.

To my shock!! the MOTEC was registering lean (17++) but the APEXi was like rich. (12++)

Since then, I don't trust the A/F gauge. I only rely on the EGT to monitor my babe, whether its lean or rich.

 

[deyes]

A/F guages are good for telling if your O2 sensor has gone bad

 

[logic]

Tell me about it. Mine currently does the blink-blink-stick thing (it'll blink from time to time, but most of the time it's "stuck" at the maximum reading).

Time for a new O2 sensor.

 

[Redsand187]

Originally posted by 4G92-T
Are these aftermarekt A/F gauge any good at all?

I have an APEXi A/F gauge (the model that incorporates a Turbo timer). I recently went for tuning with a MOTEC wide band 02 sensor.

To my shock!! the MOTEC was registering lean (17++) but the APEXi was like rich. (12++)

Since then, I don't trust the A/F gauge. I only rely on the EGT to monitor my babe, whether its lean or rich.

If you were that lean I would hope to God that you could hear it!


How the ECU works, it when in closed loop, it looks at the o2 sensor to adjust the amount of fuel it injects. Older ECUs aren't always "smart." It is not uncommon for the ECU to look at the reading, see that it appears rich, then overcompensate when pulling fuel, then see that it is lean, and overcompensate by adding too much fuel... In fact that is how they work, just with the newer cars the sensitivity is very high, so they aren't as noticeable.

In open loop (at idle) the computer ignores the o2 sensor, so you may see some plain crazy numbers/readings that stay solid.

Pretty much, at anytime it is not uncommon to see those lights bouncing around, even at WOT. Just at WOT they should not move as much, depending on how sensitive the ECU is to the reading you may not see it move at all. (remember those gauges are pretty broad)

A wideband o2 sensor is the best way to tune your car, EGT is helpful, but many conditions effect the temp. of detenation/preignition. Whereas nothing except fuel and air effect the Air/Fuel reading.

 

[EuroGSTSpyder]

just a litle Q: How far in the green should you be on WOT? I go all the way down to full..IE all the way down on the green almost...