Air/fuel ratio gauge wiring

**Filterlab** · Monday 17th August 2009, 20:21

Following my temporary boost gauge fitting earlier, I've decided to fit it in the car properly. I'd like an AFR gauge too and seemingly there is only one wire that has to be connected; to the O2 sensor if I understand correctly. Ok, I know that the narrowband O2 sensor is going to diminish the quality of the accuracy a little, but it's better than nothing, and if nothing else it'll be a good warning of potential large problems.

Anyway, is there a more convenient place to pick up a feed from the O2 sensor than underneath the car?

**p fandango** · Monday 17th August 2009, 20:36

the factory o2 sensor is only narrow band, not wide band so won't give the right reading. You need a complete kit complete with sensor & get a new collar welded into the exhaust (altho my Ferrita has already got a spare collar)

**Filterlab** · Monday 17th August 2009, 20:42

Will the narrow band sensor give a reading that's roughly correct or does an AFR gauge on a narrowband sensor simply become a lights display and little else?

**p fandango** · Monday 17th August 2009, 20:50

Originally Posted by Filterlab

Will the narrow band sensor give a reading that's roughly correct or does an AFR gauge on a narrowband sensor simply become a lights display and little else?

no-where near i'm afraid mate, my bro tried it on his VR4 & the pretty lights just scrolled from one side of the gauge to the other, not giving a constant reading at all. I've also read that T'ing off the factory o2 will also affect the ohmage so the ECU will be getting incorrect readings as well, messing up the fuelling

**Filterlab** · Monday 17th August 2009, 21:10

I'll give that a miss then I think!

Cheers mate.

**p fandango** · Monday 17th August 2009, 21:48

Originally Posted by Filterlab

I'll give that a miss then I think!

Cheers mate.

no problem mate, i know its always a good idea & nice to be-able to keep an eye on everything. But i've never worked out why the AFR's should change anyway once the car has been correctly/professionally set-up

**walter leever** · Monday 17th August 2009, 21:58

It's always nice to have extra lights on board.

(i have one fitted and it works ok,nowhere near as accurate as a wide band offcourse

,but that will come in the future.

Mine's always moving about 3leds to thye left and then back again(normal driving/same speed,so you see it regulating.

**irf** · Monday 17th August 2009, 22:43

Originally Posted by p fandango

no problem mate, i know its always a good idea & nice to be-able to keep an eye on everything. But i've never worked out why the AFR's should change anyway once the car has been correctly/professionally set-up

it depends, if you're the type to go for a simple remap and exhaust then there's no point. if you're gonna make changes as you go along then they're invaluable.

AFRs can change depending if it's summer or winter as well.

As an aside, at the Ring earlier this year, on one lap the car started feeling a bit sluggish, looked at the AFRs and they were out, got back to the car park and there was a big tear in one of the intercooler hoses.

oh, and a narrowband, as said is completely useless.

**kevin 850t** · Tuesday 18th August 2009, 01:23

Great question, thankyou all, bet mines a narrowband!! what a waste of money that was, at least it has pretty light coming from it!!

I burnt my leg today from the exhaust fumes!!, damm it was hot, melted my leg hair.

**Al115** · Tuesday 18th August 2009, 09:53

Simple reason for fitting an AFR meter is "in case something breaks" - as Irf has said...

**daveforber** · Tuesday 18th August 2009, 18:10

Well, mine's a narrowband and it works fine. OK, you don't know the actual AFRs, and it just flashes lights based on lean/optimal/rich, but it did predicted the two breakdowns I've had (which were failed battery and failing fuel pump), hence they're called 'worry gauges'. In fairness, I could have predicted both from poor performance and struggling, but the AFR gauge did say things were running leaner than they should in both cases.

To answer a previous question, AFRs change based on a number of things, for example:

Engine temperature (cold=rich)
Idling (should be lambda=1)
Full throttle (rich)
Slowing in gear, no throttle (lean)

The tune basically adds more fuel for full acceleration to reduce the risk of detonation (more fuel cools the engine slightly), and cuts fuel when slowing in gear with no throttle (no point in putting any in since the engine isn't doing any work). Temperature-wise, if you remember chokes, they essentially create a rich mixture (easier to ignite) when cold - presumably the tune does the same.

At least, that's my limited understanding.

I still think a narrowband gauge is useful, and not a complete waste of money given wideband gauges are so expensive ... especially given that you're tapping into the existing sensor, which is presumably also narrowband and is good enough for the ECU?

**cornclose** · Friday 21st August 2009, 12:12

I read the narrow band sensor via obdii and have a gauge for it (amongst many other things) on my car pc. The instantaneous value does indeed vary, as it should, but I also have an average value displayed of all instantaneous values taken so far, and another showing the average of the last 100 samples. This gives me the best idea of what's going on, and if I need some other indication, I can add it.

Car pc - it's the future!

**Filterlab** · Friday 21st August 2009, 12:24

Originally Posted by cornclose

I read the narrow band sensor via obdii and have a gauge for it (amongst many other things) on my car pc.

Is there such a thing as an AFR gauge that plugs straight into the OBDII? One that doesn't cost £400 I mean.

**cornclose** · Friday 21st August 2009, 12:45

I considered one of these before going down the custom car pc route;

http://www.autocaress.com/acatalog/D...om_Gauges.html

A cheaper alternative is this, not sure if it does o2 sensor data though...

http://www.autocaress.com/acatalog/S...uage.html#a205