Air/Fuel Meter Installation

Last updated: February 16, 1998

Date: Mon, 10 Nov 1997 22:17:45 -0500 From: Rob Robinette

I asked this question a couple of weeks ago and didn't get an answer so I dug out the Shop Manual while installing an HKS FCON and looked for the oxygen sensor wire at the ECU. I wanted to tap into the O2 sensor at the ECU for an air/fuel meter. The O2 sensor wire is a solid black wire on the only 16 conductor ECU connector. The Shop Manual calls it wire 3C. When viewing the connector from the end that the wires from the car run into it and with the locking clip pointing up, it is the second wire from the right on the top row (only black wire on the connector). I put a wire tap that accepts a blade type male connector on wire 3C so I could easily remove the air/fuel gauge O2 wire.


Date: Sun, 7 Dec 1997 10:05:27 -0600
From: "John Wise"

On my Halmeter 15-LED air-to-fuel gauge, the only times I can get it to stabilize are at idle, WOT, and a VERY consistent throttle input. At idle, your meter should read somewhere between 14.7 and 12.0 (RICH), depending on how your car is tuned. But on WOT, the meter should read near all the way rich. During cruising, the reading fluctuates very rapidly from 13.x to 16.x. Well, that's how my A/F meter functions, anyhow.


Date: Sun, 7 Dec 1997 11:13:14 -0500
From: (Carlos Iglesias)

>At idle, no lights are lit. At WOT, they're all lit. If I
>pop the throttle while sitting still, they'll all light up
>then go out, tracking the RPMs.
>Is this normal? The gauge rarely, if ever, stabilizes at
>14.7. Usually it's off either end of the scale.

Sounds about right. Since the voltage will vary from about .1 (extreme lean) during closed loop at cruise, to about .88 at the richest conditions (hopefully towards WOT), as well as idle (with no airpump). The trick is to monitor the A/F during WOT operations across the performance range, assuring that it doesn't lean out.


Date: Tue, 20 Jan 1998 00:24:13 +0000
From: (Chris Scott)

Just installed my Cyberdyne A/F gauge this last weekend. While I was at it I measured the voltages corresponding to each LED. This is what I got from lean to rich:

red       0.096 v
red       0.196 v
yellow    0.295 v
yellow    0.393 v
green     0.487 v
green     0.588 v
yellow    0.685 v
yellow    0.783 v
red       0.878 v

I did not get a voltage for the final red LED (rich). Given the trend I would expect it to be around 0.97 v.

My multimeter is rated for +/- 0.5% accuracy, so the third digit in the above values should not be considered accurate. Also this is for my sample, others may get different values. With Cyberdyne's price, I'm not sure how good their quality control is.

As this shows, the unit does not have enough resolution in the area of interest (only 2 LEDs covering 0.78 to 0.88 volts) to be very useful for tuning, but can provide an indication of going too lean.

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