A:F Gauge Hookup

[Nixon1]

Quick question..the A:F gauge wires to the oxygen sensor. So which wire does it tap into? My O2 sensors have 3 wires...2 white and one black. So which color is signal? I assume the black one? I'm hoping to hook it up today since I'm bored and I want to see exactly how rich my car is running....so prompt responses are appreciated. Thanks!

[bigred90gt]

looking at the connector (wiring harness), from the ECM, the X marks where the wire is you want to attach the a/f gauge to:
1 -0000000000 - 0000000000-20
21-00000000X0 - 0000000000-40
41-0000000000 - 0000000000-60

[Old Guy with 87 GT]

pin #29 is the signal wire for the right o2
pin #43 for the left

if you unplug the ecu harness , the pins are numbered.......i did mine this way

ps .i put the signal wires on a toggle switch so i can check the right and left o2s as needed .....pretty helpful when troubleshooting

[Nixon1]

Old Guy...you read my mind. I had already planned that, just in case I fouled out an O2 sensor before the other one...so I could check consistency between both banks. Now the question is, where the hell is the ECM and connector? Never even been near the thing. Is it in the engine bay, or somewhere in the car itself? I heard it was in the passenger side of the car, below the glovebox if I remember right..behind that panel somewhere..?

[Nixon1]

By the way..I figured out why my car was running rich. My EGR valve was frozen closed. Didn't operate at all. Never threw a single check engine light either. F*cking Fords. Lol but anyways, $80 later, the car runs like a DREAM. Still a TAD rich though so I'm gonna do the gauge thing anyways. Just a good reference point.

[Old Guy with 87 GT]

the ecu is on the passenger side ,below the dash behind the kick panel

you have to take the readings you get from the air/fuel with a grain of salt when it comes to judging the actualle stoich .......a wide band o2 reading from a dyno run is alot more revealing .........the air/fuel gauge is definatly helpful to determine if your ecu is operating in open loop and doing what it should ,but there's a wide margin of rich or lean conditions that the o2s don't really see

the gauge is a little helpful for determining wide open thrttle stoich ,but only as a method of knowing if there's somthing wrong ......if your stiotch is ok at wide open it'll peg the gauge on the rich side

[Nixon1]

Yeah, I understand that.. I just want to use it to see what my readings are at idle and at cruising, and also to see whether the motor tries to lean out at any point during operation, so that if it does I can retard the timing back until I can get an adjustable FPR.

The kick panel is the SIDE panel, not the front right?

[Old Guy with 87 GT]

Originally posted by Nixon1
The kick panel is the SIDE panel, not the front right?

yes, it's the side panel............you have to remove the threshold peice that runs under the door ,then the kick pannel is held on by a push clip .....be gentle the panel is easy to crack

[Nixon1]

The threshold piece...do you mean the door sill plate? So I have to remove that whole damn thing just to take the kick panel out? ::Sigh:: Lol... Which way does it slide out...towards you? Or is there a trick, like up and out or something?

[Old Guy with 87 GT]

the sill piece overlaps the kick panel ,you might not have to take it all the way off ,might be easier to just remove it half way

[Nixon1]

I looked at it today and see what you're talking about. Looks fairly easy. So you said it's held on by a push clip...meaning I should like brace it from behind with screwdrivers or hands and pull it outwards?

[gtnby2]

yeah pull it straight out (towards the center console) and the pin will pull out. BE CARFUL not to break the pin off...you can get new ones but with cars as old as ours they are usually a different color and look like ****.

[Nixon1]

Got the pin out no problem. Old Guy...did you use a 3 position toggle? How did you wire it? I've been trying to imagine where the primary signal wire for the sensor goes on this switch and I can't visualize it. I imagine both ECM input wires going to opposite sides of the switch...is there a third connector on the switch for the gauge then, which, depending on the switch position, completes the connection with either the 29 pin or the 43 pin?

[skiwesser]

I've been thinking of getting one of those A/F gauges too.

Are you guys saying too adjust fuel press. so it reads stoich

at WOT but it will read rich otherwise (closed loop?).

BTW is WOT open loop and part thottle,cruising speed closed loop?

[StangFlyer]

skiwesser - Yes, close loop is during idle and part throttle operation. During wide open throttle operation the EEC goes into "open loop" mode.

You cannot tune your cars fuel delivery with the EEC based on the stockish type O2 sensors. The standard style Bosch (etc) O2's are really only a basic sensor that switches between lean, stoichemetric, and rich for the most part. In a normally operating Mustang hooking an A/F guage to the O2's will simply indicate that the EEC is doing it's job and getting proper input from the O2's. With a dual gauge set up you will see the gauges toggle between each bank of cylinders on the engine (left side will go lean, while the right side will go rich, and vice versa). When you go into WOT you will see them both instantly (or should) go full rich. So, all it does is say the EEC's doing its business and fuel delivery is working basically.

In order to actually tune your fuel delivery via an O2 sensor input alone, you would have to replace the standard style O2 sensor(s) with a "wide band" O2 that can give full range A/F ratios. These are very expensive, at around $600 to $800 each, and are what the various EEC tuners using Mike Wesleys tuning software and chip technology commonly use... either on the street or on the dyno (the later is the ideal way to tune your vehicle.. i.e. an experienced tuner using wide band(s) in conjuction with a chassis dyno).

For those who would like to learn a little more about the EEC, tuning, and adaptive control I'd suggestion reading some of our older articles on the subject here:

Induction Blues, EEC-IV Adaptive Control, EEK vs. EEK, and others in our articles section...

[Old Guy with 87 GT]

Originally posted by Nixon1
Got the pin out no problem. Old Guy...did you use a 3 position toggle? How did you wire it? I've been trying to imagine where the primary signal wire for the sensor goes on this switch and I can't visualize it. I imagine both ECM input wires going to opposite sides of the switch...is there a third connector on the switch for the gauge then, which, depending on the switch position, completes the connection with either the 29 pin or the 43 pin?

sorry for the late reply
.....you have to make sure you have the right kind of switch ,there should be a simple diagram of the switch on the package it came in ........what you want is for the switch to complete the curcuit on two seperate sides with a single input .........you'd want to wire the two 02 signal wires on the seperate sides of the switch ,then wire the gauges signal wire to the center pole
.......if you can't find a diagram then use a tester to find out how the switch works........just be sure the signal wires from the 02s aren't switched together so they don't short out with each other

it's a litte hard to explain without showing you ,it might be helpful if you have a friend with a little experience in wiring to help

[Old Guy with 87 GT]

Originally posted by skiwesser
I've been thinking of getting one of those A/F gauges too.

Are you guys saying too adjust fuel press. so it reads stoich

at WOT but it will read rich otherwise (closed loop?).

BTW is WOT open loop and part thottle,cruising speed closed loop?

dan couldn't have said it any better ,
.......an air/fuel gauge is more of a diagnostic gauge, then a tuning gauge.........they can be helpful ,but there usually only acurate enough to see if you cars computer and fuel systems are working properly ,.......if you want an acurate guidline for tuning then going to a performance dyno tuner is a sound investment ,or as dan mentioned there are more acurate tuning systems on the market (pricey though)