A/F Ratio - Monitoring

Super XR7

Registered User
What is the best way to monitor air/fuel ratios on a 89? Thru the oxygen sensors, exhaust temperatures or ??

Thanks,
Mike Tuck
 
Most of the gauges I've seen & used work off the oxygen sensor. The cheapest way is to splice them into the sensor wiring (usually the black wire on the heated 4 wire sensors). Some gauge manufacturers have their own sensor that they say is more accurate (and extra cost of course). I haven't tried the one with the semi-circular bar graph, but I have the colored vertical bar scale (digital) ones on my '93 and the traditional analog type on my '94. The digital ones work quite well, as far as being able to identify when there is a problem; but I don't think either are really good tools for any kind of accurate analysis of the A/F ratio.
Jim.
 
my opinion is to do one of these below (second one is better, i will switch to it soon, because it is basically the most accurate way to monitor your O2's) (if someone has a better idea please list it.. because i will be doing # 2 this summer) only thing is you gotta find out what the voltage is for lean-rich so you know where u stand. Hope this helped. Alex L

1. Buy 2 A/F gauges and run them to you O2's so you can meter both at the same time. (most people do one, not sure why with a flip switch, you cant see both readings at the same time when you do it that way, so what good is that ? ) if you set it up like i said you can view both sides at the same time. Thats how i did mine. (but i'm changing to the one below)

2. you could get 2 Wide band O2's and get 2 volt meter gauges (prefferably digital) and hook it up, and view both that way.
 
That's a very interesting question. The signal is supposed to be less than 1 volt and, running a live scan at idle on my AutoXray I found the voltage fluctuated from .38v to .72v and occationally showed .00v. So it looks like .38 -.55v for one end of the scale (not sure whether that's lean or rich?) and .59 -.73v on the other. I agree about the 2 gauges, that's how I found the one bad 02 sensor on my'93 (wasn't throwing any codes at the time, either). On my '94 I have the one analog gauge with the switch between sensors, but the signal rectifyer which used to give a steady average reading went bad. Now the needle swings back and forth with the voltage pulses - drives me mad; one day I'm gonna put it's lights out altogether !!!
 
Using the stock sensor the narrow band is from 0 v to just under 1.0V . 0.5 V corresponds to 14.67:1 for the A/F ratio. This value is fine for idle and part throttle.

NarrowbandOutputGraph.jpg


But under boost and WOT, the stock sensor cannot help you tune with the 11.9-12.5 A/F ratios.
 
(cougarsc) (sweet pic) do you have a chart like that for a wideband O2 ? i want to use 2 wide band O2's and get 2 digital volt gauges. Thanks Alex L
 
(cougarsc) where did u get this stuff, its awesome man, thanks.. what a difference in what stock O2's read than a wide band. So does under boost and WOT also apply to tune on the wideband as well? or is that why u use the wideband O2's because u can ? Thanks again Alex L
 
sorry to disapoint you SuperCoupeSC91......but you cant just get some wideband sensors and use a volt meter to get a reading. Wide band sensors dont work that way. You need a controler in order to get a reading. The controller converts the signals so you can read them. This is why wide band kits go for big bucks. The controller also self calibrates the signal you see according to you're enviroment...as well as heats the sensors ect ect. They can not be used in place of the stock sensors as the computer cant read them. Therefore if the computer cant read them....then you cant just plug them into the stock harness. Wideband sensors are 5 wires...rather than the stock 4 wire..and they have totally different connections. If you want a wide band kit..i would go with an inovation motorsport kit(350) or a dynotune kit(400).
 
(fastsc92) oh yeah (duh :confused: ) what was i thinking, i remember i wanted to do a kit up and i was looking into it, forgot all about it... so then the best bet is to keep your stock O2's where they are then and get 2 kits and have hole pieces for 2 wide band to fit into your exhaust (but where would best location be for that then?). dam thats expensive :(... Ok now i know what i have to look forward to. Thanks for reminding me on that one. Alex L
 
Well whats nice about the dynotune kit is that you put their sensor in place of the stock sensor.....which goes to the controller....but the controller has a feature that convert the wideband signal to a narrow band signal. This way you can read your wideband ratio....and the computer get a narrowband signal at the same time. Everyone is happy and you dont need to add any holes (bungs) in the exhaust. There is no need for two sensors or two kits. If you want...do a WOT run on one bank, get a reading...then swap the sensor real quick and do the other side. Usually....one sensor does the trick.
 
Alex - I spliced/tapped into the wire on the stock sensors, which I also replaced at the same time (around 85,000m I recall). I'm going to hook-up my AutoXray again, when I get time and monitor the voltage from idle to WOT. With their EZ computer link I can download, print and graph the live recorded data. Best investment I ever made - it's scans all OBD 1 & 2 vehicles and included all the cables + one for the port on the computer.
Jim.
 
The dynotune kit seems like the way to go, very nice but pricey. What else is new for these cars. This may be a dumb question but can the exhuast temperature tell you if you are rich or lean for a given rpm-load? I have completed a rebuild with a lot of add ons and am not sure how my A/F is running.
Mike Tuck
Super XR7
 
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