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Need voltage output from 02 sensors.

3903 Views 11 Replies 3 Participants Last post by  87frankenstang
Wideband O2 to AFR controller to ECU

Hey guys.

I installed my MXT-L AFR controller along with a bosch style wide band in my driver side bank. I need to know the voltage output from my o2 sensor that my ECU needs to read lamda (or shall I say lean/rich) as I can define this in my controller.

I found this: Oxygen sensors | Mustang Forums at StangNet . It stated that at lean it will read less than 400 milivolts and at rich it will read over 600 milivolts with an overall range of .1 to .9 volts. So I did the math and this is what I got:

.1 to .4 volts is lean
.5 volts is lamba
.6 to .9 volts is rich

I included a screen shot of the factory defined analog output voltages for the MXT-L. By FACTORY DEFAULT it's allocating 1 volt as lamda, .5 volt at full lean and 1.5 volts at full rich. I will change this to the aforementioned calculations. Do my calculations look and seem right? Can anyone confirm this information? I just want to make sure I have the right info and only need to program my controller once...


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.45 volts is the crossover point and lambda (~14.7 AFR) in a fully-warm early Ford EGO sensor.

Lean is less than 450 millivolts (.45 volts), and rich is more than .45 volts.

My HEGO's tend to stay below .4 when even slightly lean, and above .6 even when just slightly rich.

The problem is the narrow EGO sensors are not linear, they behave partly like switches. I built a warning system for my car that samples the HEGO's. My home made system looks at the HEGO's and other things just to give me a warning idiot light. It considers any fully open throttle voltage below .55 as lean, because I want things on the rich side at WOT. It inhibits giving a warning on any closing throttle movement.

I did this because my Innovate LM2 with wideband was so unreliable, and I wanted fail safe warning lights. When the LM2 locks up, and it does at times, it can lock with good mixture.
I'm wondering if I should just install the other bung now and do my original plan of running both factory narrow bands, and leaving the wideband completely standalone.

All this talk of them "locking up" kind of has me worried. I don't want my car to start running like **** at 70mph on the highway, have to pull over and cycle the key just to keep on going because a GUAGE decided to malfunction.

Old man, what is your homemade setup? Are you even using a wideband?
I have a LM2 wideband, but it is somewhat unreliable. It is not the Bosch wideband sensor that is trouble, it is in the design of the LM2. I absolutely use the wideband, but the LM2 occasionally locks up when logging. I'd say 1 out of 3 or 4 times it locks and I don't log an O2 reading through a full run.

My homemade system is a series of voltage sensors that can be programmed to any voltage as an alarm. The alarm can be excluded by RPM or by throttle position.

The alarms can be programmed as a caution or as a stop. I did this because I had a couple lean outs where I lost a piston. One was from a hose cracking loose from the SC inlet, and one was from loss of fuel pressure. Even though nothing gets hurt besides a piston, a piston is expensive to replace. Now I watch oil pressure, fuel pressure voltage, the wideband sensor, the narrow band sensors, engine knock, and water temperature and assign throttle positions and RPM where they take effect.

I have gone back to a warning light system instead of gauges (gauges still there), because I never can watch gauges when going down the track.
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