I installed an autometer air fuel ratio gauge last week, and after battling with a blown fuel pump I finally got the car to run normal. When I drive the gauge jumps around like on night rider and seems to be way too sensitive. I can't really tell if I am rich or lean. If I stay hard on the gas it will say I am high stoich (which is good) but often jumps down to lean and than just bounces back and forth erraticaly. I have checked all of my connections and they are good but I can't tune the car if the gauge won't stay still for more than a billionth of a second. This is with the stock fuel presure regulator. It acts the same with the GM vacuum one as well. I had that one set at 10 PSI at idle and roughly 15 PSI at WOT.

get used to it, thats what its supposed to do, its useless. Its just a fancy volt meter reading your O2 sensor voltage. Its supposed to swing back and forth and thats what the o2 sensor does. The stock sensor can only detect rich or lean, not how rich or how lean.

About the only thing its good for it to make sure you dont run lean at wot, but other than that its useless.

nsimmons id right...

I just put one in my car and if you read the instructions they tell you it will jump from rich to lean while in closed loop to try to maintain 14.7. But the way I look at it, I don't care what it does at "highway cruise throttle" I just want something to help me tune for WOT. I did help me in finding out that a stumble I had was fuel pressure related and I hope it will help me in tuning my new vafpr.

I just hope it doesn't get annoying jumping around like that for everyday driving...

would a wide band O2 sensor fix that?

A wideband sensor by itself will not help without the electronics to go with it. You may have seen the DIY wideband sensor project (http://www.diy-wb.com/). It is somewhat complex and not for the squeamish. I have collected all of the parts (minus the $100+ sensor) and intend to put it together someday. Someone referenced at the site has layed out and sells a PC board for it. They are cheap. Buy two it case you screw one up.
I have included the Voltage/AFR table claimed for a working unit.
For those of you who hate the blinking lights and do not want to build the wide band unit (it’s intended for tuning only) you can build an analog meter that has better swing range than an ordinary analog voltmeter. I built one using a Radio Shack 15V meter and used an op amp to multiply the O2 sensor voltage by 15. It’s like watching a metronome at AFR 14.7 and tells me that I’m running rich under throttle. Works great and does’t hurt the brain with blinking lights.


Vout Lambda AFR FAR
1.40 0.685 10.08 0.099
1.45 0.695 10.23 0.098
1.50 0.706 10.38 0.096
1.55 0.716 10.53 0.095
1.60 0.727 10.69 0.094
1.65 0.738 10.86 0.092
1.70 0.750 11.03 0.091
1.75 0.761 11.20 0.089
1.80 0.774 11.38 0.088
1.85 0.787 11.57 0.086
1.90 0.800 11.76 0.085
1.95 0.813 11.96 0.084
2.00 0.827 12.17 0.082
2.05 0.842 12.38 0.081
2.10 0.857 12.60 0.079
2.15 0.872 12.83 0.078
2.20 0.889 13.07 0.077
2.25 0.905 13.31 0.075
2.30 0.923 13.57 0.074
2.35 0.941 13.84 0.072
2.40 0.959 14.11 0.071
2.45 0.979 14.40 0.069
2.50 1.00 14.70 0.068 *
2.55 1.037 15.25 0.066
2.60 1.077 15.84 0.063
2.65 1.121 16.48 0.061
2.70 1.168 17.18 0.058
2.75 1.219 17.93 0.056
2.80 1.276 18.76 0.053
2.85 1.337 19.66 0.051
2.90 1.405 20.66 0.048

4.00 Free Air
* = Stoichiometric Point
AFR = Air/Fuel Ratio
FAR = Fuel/Air Ratio

In closed loop the ecm tries to AVERAGE 14.7:1. So you'll see the O2 voltages swing over and under .45v.

The stock O2s are of a switching type. They see richer then 14.7 and leaner then 14.7, that's all. They are effected by EGT, and backpressure. While a heated O2 helps slightly with the EGT, the stock type aren't meant to do more then just switch.

If you want to read AFR at WOT, you need a Wideband, or to learn how to read spark plugs. And with some of the newer fuel mixtures, you need to be real good at reading plugs to really see what's going on.

I've been using the DIY-WB, and have learned alot in just watching it. I also, have about 10K miles on it now. It makes dialing in a chip really easy, you can actually see the accleration enrichment, and then WOT AFR nicely.

Grumpy,

You are in Dayton. Where abouts are you? I am in Dayton too.

I originally had the Autometer unit and thought it read way too fast. Especially for something as inaccurate as our switching type O² sensors.

I sent it back and got a Nord-Skog A/F gauge, and it's much much better as far as how it reads. It just doesn't have the eye-candy appeal that the Autometer gauge does. But hey, it was also $20 cheaper.

Grumpy
It's good to hear that the DIY-WB works well.
I was wanting to know what visual tool you used with the box. LED's, analog, digital? What worked best?

Dave