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O2 sensor and MAP sensor voltage questions

Old 11-05-2003, 04:50 PM
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Default O2 sensor and MAP sensor voltage questions

on an O2 sensor (civic O2 sensor) what voltage levels correspond to what what A/F ratio?

on a MAP sensor what is relationship between output voltage and psi in the manifold?

on an oil pressur sensor what is the relationship between voltage and oil pressur?

same questions with the TPS (Throttle position sensor)

To control the injectors does the ECU increase the frequency of the pulse or does it modulate the duration of the pulse, or is it combination of both? What kind of modulation is used on the pulse (square, sinusoidal, etc..)?

what I want to do is to hookup my laptop to read from these sensors and control my injectors. the techy stuff I already know and have done before, but the automotive side i have no idea. In the end what I am planning to do is have the computer optimize the fuel injected into the car for the most HP, basically I will implement a digital control system that will automatically to implement the optimal A/F ratio under all circumstances, either that or i will just plot out my stock fuel maps by reading the injector pulse widths and frequency and manually adjust them. the whole things seems doable.
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Old 11-05-2003, 05:20 PM
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Default Re:O2 sensor and MAP sensor voltage questions

Interesting questions... got something special planned?

O2 sensor:
1v=17:1, .3v=16:1, .5v=14.9, .7v=13.8:1, .9v=12.7:1.

TPS:
This is a derrived percent. Basically, it would need to be calibrated with an offset. Then it's a percent 0-100% between that an 4.49 volts, if I remember correctly.

Oil: I Dunno..
MAP: I dunno (veyr secret information from what I'm gathering.. No one wants to share this because it's being used in datalogging applications..)

Injectors:
Moderates duration, don't know the moderation off the top of my head. I'll update this post when I get home..

Your Project:
Very doable, very interesting. Depending on your OBD setup, your difficulty in application will be great.

I'm, personally, working on OBD0 (pre-OBD) setups, and have a datalogger written to access some of the sensors you're looking for.

Also, if you haven't heard, you should check out www.PGMFI.org. That is where all the ECU hacking takes place. The seniors PGMFI are very knowledgebale, and have gotten the Honda ECU hacking world to the point that we're at. They deserve a huge applause.. check 'em out.


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Old 11-05-2003, 07:55 PM
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Default Re:O2 sensor and MAP sensor voltage questions

damn thanks for the info man, you are a fountain of knowledge. I am not reprogramming the ecu so weather it is ODB0 of ODB69 it does not matter. My plan is to intercept the signal coming form the ECU to the injectors and override them with mine. I think I can do a decent job by just reading the RPM, O2, and MAP sensor for now. BTW when you look at fuel maps what are axises (RPM,O2 and pressure)?
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Old 11-05-2003, 09:57 PM
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Default Re:O2 sensor and MAP sensor voltage questions

Honda maps are 2 demensional. RPM vs MAP. The newer i-VTEC OBDII ECUs are 3 demensional with RPM vs MAP vs Cam position.

But anyway.. there is also Low Cam/High Cam on the VTEC ECUs. Which are two different maps that engage at different points based on VTEC oil pressure, RPM, speed, and engine load. Crazy, eh?

Oh, hey, I uploaded some documents for you that a buddy of mine collected. Maybe they'll help you out. ::shrugs::

http://www.DriftKids.com/HondaDocs
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Old 11-05-2003, 11:14 PM
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Default Re:O2 sensor and MAP sensor voltage questions

humm thanks again,

Upon doing more reading, I might go the easier route and make more of an AFC kind of setup. basically let the ECU do all the work and have my laptop "massage" the input form the sensors to trick the ecu. that would be simplier but less satifying and less flexible. thanks man if you can think up of more info please tell me.
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Old 11-06-2003, 06:09 AM
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Default Re:O2 sensor and MAP sensor voltage questions

i'm trying to set up datalogging with a techedge. i need to know how the map voltage coresponds to actual pressure values. please, someone has to know this.
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Old 11-06-2003, 09:24 AM
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Default Re:O2 sensor and MAP sensor voltage questions

You'll just have to figure it out. Creating formulas is part of the game...
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Old 11-06-2003, 02:27 PM
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Default Re:O2 sensor and MAP sensor voltage questions

it is close enough to the truth that honda map sensors are 1.7bar absolute.

so... 1.7bar absolute = 5v 0bar absolute = 0v and there is a more or less linear curve in between.

See PGMFI's wiki for more info on absolute pressure.
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Old 11-06-2003, 02:46 PM
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Default Re:O2 sensor and MAP sensor voltage questions

Assuming OBD0 datalogging output for the TPS is the same as OBDI, 9E = 3.1V which = about when boost starts.


figure the rest out from there

9E is what I have my alochol/water injection code set to turn on the AC clutch for the electric pump.... assuming I ever get sold a working turbocharger.
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Old 11-07-2003, 09:39 AM
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Default Re:O2 sensor and MAP sensor voltage questions

O2 sensor: 14.7:1 AFR at 0.45 volts, anything higher is richer and anything lower is leaner - but noone can tellyou by how much. Stock O2 is calibrated for one thing and one thing only - stiochiometric.

MAP sensor: It is a 1.8 bar absolute sensor, not 1.7. It is linear for pressure:voltage, so graph it out via these two points: 1.6xx volts with key on engine off and 4.5xx volts at 10.6 psi. Due to physical construction, which limits MAP sensor diaphragm travel so that the full 5 volt referrence voltage return is never acheived, you never read past 9.25 psi OBD0 and 10.65 psi OBD1.

Oil pressure: It's a simple switch, you hit about 15 psig oil pressure and it opens the circuit with the warning light on the dash.

TPS: easy ----. Reads .5 volts at idle, and 4.5 at WOT. Simple potentiometer. Everything inbetween falls where it may. Honda service literature claims anything over 4 volts TPS triggers open loop, but it seems to me that happens before that point.

Injectors are always a square wave, and frequency is a function of engine rpm. From there pulsewidth/duty cycle is manipulated as required.
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