Calibrate an AFR meter for use with wideband O2

[fscott]

Yesterday while tuning my bike, I was watching both the O2 bar graph in megatune, and my AFR meter mounted on the bike. I was geting frustrated because they refused to agree with each other.

Since I knew what the LC-1 was sending to both the MS and to the AFR meter, and the MS and Megatune were programmed to accept the output, the problem had to be the meter.

Today I made a simple rig to test the meter against various inputs. There's a AA battery, and a 10Kohm variable resistor from radio shack. And you need an accurate multimeter. In other words, not a meter from Radio Shack.

Wire it up like in the picture, and connect it, along with a multimeter, to your vehicle. The engine doesn't need to be running. Just turn the key on so that your meter powers up. Make sure that the wideband controller is disconnected from the meter, you don't want to be putting voltage throughit.

Now, you should see a voltage on the multimeter, and by adjusting the potentiometer, you can change that voltage and change the output of the AFR meter. Be careful, you can put 1.5 volts to your meter if you turn the knob all the way over. It didn't hurt mine, but yours may be more delicate.

By slowly adjusting the knob, you can find out what voltage will light a specific light on your meter. Take notes.

For extra fun, you can graph the results and come up with the best two pairs of values to enter into the LC-1 programmer.

I found with mine that in order to light up the Stochiometric light on the AFM, I needed 0.621 volts. That's far off from the .5 volts that I was expecting to see, and it acounts for the gauge being so far off.

With new output values in the LC-1, the gauge follows MegaTune's numbers perfectly.

One nice thing about this is that it's no longer of any importance to buy a high quality AFM gauge. Go ahead and get the cheapo one from the auto parts store. Since you can calibrate the LC-1 to it, it doesn't matter if it's not accurate!

Fred

[kanenas]

You might want to rethink your reading matching solution. If I understand your setup correctly, your self imposed bias on the O2 signal goes to both your ms box and your afr meter. That means that the ms gets the wrong mixture signal and tries to compensate using arbitrary values as a reference.
There is no easy way to branch one signal and change only one leg of it, the other side will be affected as well and more complication is needed to accomplish what you want.
d.

[fscott]

You might want to rethink your reading matching solution. If I understand your setup correctly, your self imposed bias on the O2 signal goes to both your ms box and your afr meter.

I see what you're saying, but it's not a problem with this setup.
I'm using an LC-1, which has two outputs. Output 1 is currently sending a wideband signal to the MS. Output 2 is simulating a narrowband sensor and is outputting to the AFR meter. The calibration that I did only affects Output 2. The result is that now the MS and the AFR meter are getting and displaying the same info. Before I did this calibration, my AFR meter was lying to me, which made tuning very hard.