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-   -   MAP/MAF/O2 remapper? (

tangomar 11-11-2008 06:00 PM

MAP/MAF/O2 remapper?
Some time ago I saw a thread on Jaycar Electronics.
It seems to me that it should be relatively easy to make it using a microcontroller that takes MAP/MAF/O2/EGR sensor and remap them.

There are some super-cheap parts with DA/AD and microcontrollers like this ( The only problem is what is the range needed?

What do you guys think?

Funny 11-11-2008 08:13 PM

Sorry I am of no help here, but I am interested in the concept. Making a vehicle burn less fuel (aka De-tuning like the XFi) would allow us all to conserve quite a bit of fuel. Checked out the links and the controller for it is about $60 and the Fuel re-mapper is about $80... $140 isn't all that had to recoup with and increase of 5 MPG.

I am anxious for this thread to blossom into a spring project. :D

tangomar 11-11-2008 11:12 PM

The microcontroller + AD / DA isn't that expensive (MCU AVR 128K FLASH 1.6V 44-QFN - ATXMEGA128A4-MU).
$7 + some basic PCB + voltage regulator, maybe one op-amp to amplify the DA signal... I would guess ~$20. But I don't know too much about PCB pricing.

Duffman 11-11-2008 11:34 PM

If you can program the amtel, you wont need the jaycar kit.

I dont have a car right now that I could use this on but I am still interested in the project. Does anybody have a good link on a wideband o2 sensor wrt to its outputs?

tangomar 11-12-2008 02:02 PM

Clearly you don't need the jaycar.

My questions are:
1. what is the bandwidth requirements for MAP/MAF and O2 sensors?
2. how many channels are really needed? On some cars we have 4 O2 sensors. MAF or MAP are 2 other analog signals. That would bring the number of required DAC to 6. Is this all (note, there aren't microcontrollers with 6 D/A channels, probably we need to use PWMs or something like that).


drivenByNothing 11-14-2008 05:57 PM

From what I understand, you want to intercept the signals before they reach the ECU and then send the ECU the altered output in order to trick it into running different timing and fuel values based on the faked parameters.

As far as the O2 sensor goes, I'm working on some code right now to intercept the true signal and then generate an altered signal that the ECU will believe is from the O2 sensor. Narrowband O2 sensors are pretty simple in the way they're used by the ECU. The ECU only really cares if the O2 voltage is high (~0.8V) or low (~0.2V). The sensor itself outputs voltages along a sinusoidal wave pattern, but the ECU only checks to see if the value is high or low. If the value is above .5V, the ECU believes the engine is running rich. Below .5V, the ECU thinks the engine is running lean. It basically just keeps adding fuel until it sees a rich value from the O2 sensor and then starts cutting fuel until it sees a lean value.

In theory, this allows for control of the fuel system in closed loop. Taking in other parameters to determine load could allow one to run super lean under highway driving conditions.

Voltage output from a microcontroller is most often in the form of PWM, but this can be corrected with a low-pass filter (basically just a resistor and capacitor). The filter will turn the digital PWM into an analog voltage that the ECU is looking for.

Basically, my setup is taking in O2 voltage and referencing a cutoff value. The output will be relatively the same as the input, but anything above the cutoff value will be put out as ~0.8V. The lower the cutoff value/voltage, the richer the ECU will believe the engine is running. As it reduces fuel, the input from the O2 sensor will report a lean condition. Once the frequencies of high and low voltages reach a predetermined point, the microcontroller will output a stoich wave pattern.


jtgh 12-02-2008 03:51 AM

this is called piggy backing.

or a liar box. (some commercial boxs , lie on inputs and to the actuators (injectors)

why do this, ?
you will trip up and cause the ECU to go to limphome when it discovers your messing with the inputs. (each is different and you'd have to learn yours the hard way)

course you can do small changes, as many have done.

but any change will be altered by the O2, unless you have this remapped it,as you say.
in analog electronics this is just offsetting. (gain)

if you really want to do it right, just buy a Megasquirt and tune it.
one path , all solutions and no surprises.

I have one on my sidekick and was doing lean burn. (i designed a PNP harness and it uses a stock sensors and a wide band O2)

it does work but there are lots of down side. Nox for one . Ping is the other.

i am now running a special cam shaft . I am retuning the car for this new low end torque mod. ( i can enter 5th gear sooner and this is great around town)
no data, got lots of work tuning it.

One trick i have learned and not seen here is adding a R/C (resistor cap ) filter on the
TPS output, (pot adjusable) to limit the fast foot Enrich mode.
this will for sure save gas, but car will be slugish off the line or passing,etc.
(a delayed slugishness)

thanks for the post. dont let me detract you. Just wanted to point out other options.


dcb 12-02-2008 09:32 AM

Sure it is doable, a basic arduino or clone can handle it if you want to make it easier to get started. You will get the most bang for your buck by focusing on the O2 sensor IMHO, see also EFIE. Some folks have just added (subtracted?) an offset voltage to lean out the mixture, even on the narrow band sensors, but you could also hold the high signal longer or the low signal longer with the microprocessor if you wanted more precise control.

your o2 sensor cannot handle much current (an analog voltmeter used to measure its output can fry it) and is somewhat expensive though, so proceed with caution. And you already know (or will research) all the caveats of running your engine too lean.

drivenByNothing 12-02-2008 11:50 AM

to jthg:
I'd love to do the megasquirt setup, but I just don't have the resources right now (ie time and money).

to dcb:
I bought the EFIE manual a while back and built the circuit. I don't think I ever got it to work, but I'm pretty sure that all it does is add an offset to the voltage generated by the O2 sensor. This would mean that the computer would never see a lean value and would most likely go into open loop to eliminate the faulty O2 signal it's seeing. Using a microcontroller, low and high values can be generated based on the output of the sensor and their duration can also be controlled.

I'm fully aware of the consequences of running lean, and will be taking some extra precautions to prevent adverse effects. At least this is what I'm hoping to do.

In the meantime, I'm trying to get as much data about the Saturn PCM as I can. I have an extra OBDII PCM now and I'd like to find the map tables and eventually change some values.

jtgh 12-02-2008 03:41 PM

sure you can. it's easy.
but i bet the time and money spent , modeling an O2 sensor will vastly exceed
just the one parameter box setting on MSquit that sets where you want.
Where you want the cruise stoich to be. (wide band sensor is best)

consider this:

the factory O2 is 14.7:1 ,
it is non linear, to the point of acting like a switch. <<< a serious limit.
it literally says, I'm too rich, not now,, Im too lean.

The stock ecu is coded to swing around stoich. (only the O2 know it)
the swing is for 2 reasons.
1: the O2 is a switch and the ECU can not calc. the next point (nonlinear)
2: the ECU is coded to waste fuel to keep the cat lit off. (sad huh)

a wide band sensor cures that.
one can calc. 16:1 and come close , then fine tune it on the fly.

I know people make O2 offset boxs (scalers) .
I do know they are very unreliable . (try it )
the reason is because the O2 was never ment or designed to do anything other than stoich.

Just hate seeing people pound their heads on a factory 02.

then comes the 02 monitors, that all new cars have and are all different.
the EPA spec. is a constant ,the application of the monitors are totally unpredictable.


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