Lean burn: making it visible

[TRI]

We've too much traffic over here to concentrate on the gauge all the time. That's why I'd like a LED to show me if the engine is operating in lean burn modus. The LED will be placed somewhere in the dash. The signal would be the first o2-sensor going to zero voltage. The signal should be found somewhere in the ECM pins. I'm no electronic developer. The circuit should be fairly easy. The simplest thing I can think of is a transistor acting as a switch.
Any ideas? Thanks in advance!

[RobertSmalls]

I agree, there is a need for a fast-responding lean burn indicator and predictor. I want a gauge that tells you whether you're in lean burn with a big green LED, and if so, how much harder you can squeeze the throttle while holding LB. I picture this in the form of a needle on a large dial, and it must respond very fast so you can dial in the maximum amount of lean burn in a second.

There already is a lean burn indicator, in that a ScanGauge can read your O2 sensor voltage and display a "0" if you're in lean burn, or some number higher than 50 if you're not. Oxygen sensor voltage should be the basis for the LB LED.

The threshold of lean burn happens at a certain fuel injector pulsewidth. That corresponds to a certain instantaneous mpg in each gear. How to display a pulsewidth on a big analog dial? I have no idea.

[TRI]

Again, I'm no electroengineer but maybe someone can join in. This is the schematic it COULD look like, very simple indeed. The o2 sensor voltage would be on the left side giving the input. On the right side the LED will take place with a resistor, either between the C and GND or E and GND depending on how the transistor should work. If it's closed voltage between C and GND would be good for the LED to light it up.
BUT AGAIN I'm just guessing here. Please help me out here.

[Mike Dabrowski 2000]

Set PIMA to activate assist below 100 MPG, and there is your indicator.

A simple buffer/comparator circuit is used on my dual rate grid charger, which would work nicely.
http://99mpg.com/Data/resources/down...d_charger1.pdf
The O2 sensor output is probably high impedance, so your circuit may skew the sensor output,and mess up the O2 detection, so one would want a high impedance op amp buffer to read the voltage without loading it, then an op amp comparator circuit to turn on the LED when the O2 voltage crosses the lean burn threshold.
U1C and U1D are buffer amps.
U1B is a comparator.
The target voltage is set with Vset potentiometer connected to U1C.
The O2 sensor signal would feed right into U1D
The output of U1B would go to the lean burn led through a limiting resistor instead of the relay shown.

The circuit is set up to turn off the relay when the battery volts gets larger than the setpoint, to make it turn on when the voltage is less than the setpoint, simply reverse the input connections on the comparator U1B

[TRI]

Thanks, Mike. I perhaps understand what you mean.

In the manual I've seen that the primary O2 sensor connectors are D4 and D10 of Connector D of the ECM in the pass. footroom. I'd get the signal there and feed Pin 12 of the OP with it after that series of two resistors and one potentiometer?

[Mike Dabrowski 2000]

Where you mount the circuit, and where you get the power and ground for the circuit, and how the circuit power and signal is filtered will be very important when trying to measure that analog voltage in the middle of all of the electrical noise at the ECM.


Determine range of analog voltage from O2 sensor.
Determine signal when in lean burn.

Get an op amp,reference regulator, pot, and a small plug in prototyping board and test and adjust your circuit on the bench.
Use a second pot to represent the O2 sensor signal on your breadboard.

The precision reference diodes across the threshold pot make the circuit threshold stable under varying power supply voltages.An LM7805 voltage regulator will also work.

[uhtrinity]

Here you go, it was posted here over a year ago:

Monitoring Factory Oxygen Sensors, Part 1

Monitoring Factory Oxygen Sensors, Part 2

I have a kit, just haven't put it together or installed it.

[TRI]

Thanks very much! Just what I was looking for.

[Mike Dabrowski 2000]

Cool
I missed that one

[retepsnikrep]

I prefer the pic project approach in either of two ways.

1) Use a pic analog input to measure the O2 sensor voltage at the ecm and drive a display/leds or whatever based on the voltage. very easy.

2) Use a pic plugged into the odbII port sending the scangauge codes and displaying the received data on a screen or again driving leds. More difficult. But we know the codes reqd from the scangauge data. plus you could just plug this in like a mini scangauge.

I might have a go at a pic version of No 2 above when i have finished the A123 install and my multisubpack cycler.

If we get an accurate voltage reading via this then it might be able to corelate the voltage with the lean burn activation point so we could then have a display which showed how much throttle you could get away with before lean burn would drop out. i don't quite understand the relationship but certainly room for some experimenting.