I need help with an A/F meter.....

[Frank B]

So I buy this air/fuel ratio meter off of Ebay, http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=014&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=330053082200&rd=1,1

It looks good, seems like top quality, the board, led's, wire, case, all of it.

Anyway, I hook it up today just as the directions direct me to. Green wire to negative battery terminal, white to O2, bare wire to ground near the O2(I put a short screw in the cat heat shield), orange to ignition, yellow to dash lights.At first it seemed to work fine. It was at stoich when idling cold and as it warmed up it went towards the lean side a mark. While decelerating down a hill off the throttle, it's all the way lean. When floored it's rich, sometimes. But, when cruising down the road at a steady speed it bounces back and forth from full lean to almost full rich. Sometimes full rich, sometimes just stoich but very eratic. Is this a sign of a bad O2 sensor, or maybe a bad ground? This is my first so maybe I did something wrong. I'll probably just pull it off and try again some other time.

[mikeshoup]

Your car is fuel injected, right?

 

The meter will bounce back and forth when cruising. What you're watching is the computer constantly adjusting the mixture trying to maintain it at stoich.

[GeneralDisorder]

O2's bounce a lot - especially old ones. That's just how they report. The ECU averages the readings over a short time period, and I would think your meter would be doing something similar. Newer O2's bounce faster, and start to slow down as they age.

 

GD

[jeffast]

it's because you don't have a wideband o2 sensor, standard o2 sensors just read rich or lean thus the bouncing a wideband will give you an accurate readding of how lean or how rich, or you can just us it to keep an eye to make sure evrey thing is normal

[nkx]

that thing is pretty cool lookin. i had an autometer a/f meter and could never get it to read right. then again, it didnt have as many wires to connect either. like jeffast said, theyre pretty much used for getting a good idea of what your afr is at. youre gonna need a wideband O2 if you plan on doing any accurate tuning.

[Durania]

Their also a good piece of eye candy for your dash.

[jeffast]

Their also a good piece of eye candy for your dash.

definatly looks cool i'm sorry i'm really tired i'll edit the first one tommorow to make more sense

night all

[Frank B]

The car isn't FI, the A/F meter is on my hatch at the moment. I've never fooled with one of these before so I'm really not surprised that it's going to take more to get it right. I think I'll just pull it all off today, and resume when I can get a wide band O2, and a chance to learn more about it.

Thanks for the replies.

 

I'l get a pic of it today, because it does look nice on the dash .

It actually looks better than the dash!

[Skip]

The wide band set up is going to cost significantly more.

 

I keep the type you have on all my turbo'd cars.

 

Another tip is to use a hose clamp to fasten a wire to the body

of the 02 sensor, run this wire to a ground point close to the ECU's ground.

 

Corrosion and rubber isolation mounts can cause

the exhaust system to isolate itself from ground.

The 02 sensor needs this ground to communicate with the ECU properly.

[Frank B]

Thanks Skip, I may try that. Will it settle down the eratic bouncing between one end of the spectrum to the other? Here's another question, when, or if I put a weber on this thing, I'm going to remove the ECM and such. Not the emissions stuff, just the ECM and maybe change the ignition(still working on that). Is there a way to retain the O2 for the use of the A/F meter without the ECM?

[Skip]

Hi Frank

Inanutshell

no...

yes..

 

As mentioned the A/F meter is a simple voltmeter

It is reporting the output voltage of the 02 to the ECU.

 

It is not a variable output as some suspect but more

of a digital output - not really but it

outputs a high voltage when rich, low when lean.

 

The bouncing you see is the way the ECU tries

to maintain the proper stoichiometric ratio given the

unit is in closed loop (i.e up to temp and not at WOT).

 

Yes, with a Weber even without the ECU, the 02 sensor will

show you the rich/lean state of the mixture and the bouncing will stop

(the ECU is no longer controling the mix).

This is a good way to see if the jetting of the Weber's different stages is ~ correct.

 

But is no substitute for a good wide band setup.

[Frank B]

That was the idea, to help tune the weber.

Thanks for the input.

[Frank B]

Well I just ran into town, 10 miles round trip. And on the way the reading hovered in the lean area of the meter, on the way back it hovered in the rich area. Never in stoich except at idle when I first started it. I'm confused at this point. I tried to watch it to understand what's going on and it doesn't make sense to me. Except when I first drove off when the engine wasn't up to temp yet. Then it behaved in a way I understood. Full throttle it was rich, off the throttle it was lean. I'll get it off later.

 

Thanks for the replies

[GeneralDisorder]

Except when I first drove off when the engine wasn't up to temp yet. Then it behaved in a way I understood.

 

The O2 does not begin reporting at all until it reaches a certain temp. So when you first start it, what it's showing is not accurate.

 

GD

[Frank B]

Then what was creating the signal? I always let it run for 5-10 minutes before I drive off on a cold start, that should be enough time for the O2 to get up to temp. The coolant isn't, but the exhaust is hot.

[jeffast]

operating temp for an 02 sensor is like 6-900 degrees, most cars exhaust is not hot enough at idle to get accurate readings, thats why most newer cars use heated o2 sensors,

[GeneralDisorder]

Yeah - they don't even begin to report till about 550 degrees. That's actually the reason the O2 is so close to the cat - the cat gets very hot, and helps to heat it faster, and to retain that heat under long periods of idleing. A lot of engines will cool down to the point that the O2 will stop reporting under idle, so they use the 3 or 4 wire heated units.

 

They will start to report at lower temps, but are NOT accurate. Thus your strange readings till it's all completely warm. If you want accurate readings at lower temps you need a heated unit.

 

GD

[Frank B]

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