Urban Business

k many people hook up the blue wire on the safc or vafc to the o2 sensor to read air and fuel mixtures. this works absolutly great, its just as accurate as a wide band o2 scanner. ive searched and havent seen any of the following information about how this all works together with in the *afc's

hook up the blue wire to the o2 sensor signal wire. you can do it anywhere on the line itself or at the ecu (pin C15 or 16 i believe). its a signle white wire at the o2 side and the ecu side. you can find it easily (ecu side) buy cutting back part of the harness loom. look for a really thick brown insulator. in that insulator is the white wire to and from the o2 sensor. *be sure to use a larger guage (thinner) wire when hooking it up* (super low amounts of current pass thur this wire, too thick of a wire the ecu ***** up and throws codes for the o2 sensor) once the blue wire to the afc is hooked up start the car. goto the main menu, arrow down to "etc". once in the "etc" menu goto sensor check. voltage off the o2 sensor will be listed under "input 2" or "in 2". it mesaures up to one thousanth of a volt. when you first start the car you will only get a reading in the hundreths of a volt. this is because the o2 sensor is only usefull once heated.

how to tune.
o2 voltages rage from 0 to 1. 0 being lean as hell and 1 being rich as hell
.500 - .600 volts corresponds to a stoichiometric (14.7:1) air fuel ratio. this is a dead nutz air fuel ratio. not rich not lean. anything higher than that correcponds to a more rich mixture. anything less than .500 volts translates to a lean mixture. anything over .600 trans lates to a more rich mixture. optimum performance during WOT is a slightly rich mixture.

now the crappy part:

all of the normal monitoring functions of the afc are completely useless when you are runnig the sensor check, ie you cant see wtf their doing. this hurts in 3 ways: rpms are not known, throttle position is not known and percentage of correction is not known. also you cant record any data

ways around that:
rpms, watch an external (not stock) tach
throttle position, watch your throttle voltage in the sensor check menu. i dont know what the voltage to percentage conversion is, hasnt affected me b/c my "high throttle" is set to 30 % (relitavily low)
% of correction: no clue havent figured that one out yet.

basicly you want to watch your voltage and keep an eye on your tach. note where the voltage is at what rpm, i tune per 1000 rpms so its quite easy to tell what range i need to adjust with in the rpm based settings.


why the blue wire does that it does:
the blue wire is put on the afc's as another pressure signal for sr26 (or is it rb26?)motors (skylines). since its not in use for us it can be hooked up to another sensor in which its voltage fluctuates based on sate of the engine. you can hook it up to sonething beside the o2 sensor if you want to monitor that sensors or devices performance. its quite cool because its considered a seccond input by the afc and the afc itself does a great job or monitoring its voltage.

any other info of use tag it on. i ddint find much info on how the o2 sensor and afc could be used in conjunction besides the obviouse, external a/f meter (monitor) afc (tune) combo.





[Modified by TorteX, 2:34 PM 8/26/2002]

Urban Business

this help anyone?

FUP23

Im to poor to buy one os those ;(

FredoTheChimp

me

matt_sb2000

Pretty cool, we will have to try that on the neon. Thanks.

dogpile5

that trick only works on the SAFC. the VAFC uses the blue wire to keep VTM voltage to the ecu so node CEL shows up. i originally learned that trick from DSM owners who rely on o2 readings a lot more than we do. never posted it though, to you my friend!

Urban Business

. i actually rely heavily on my o2 readings. i didnt find any info on it w/ the safc so i just figured it out =P

DOHCtorJT

You are a god. Thanks a lot! I've been wondering how in the hell I get to that reading. I hooked up the blue wire to my o2, and never have been able to check the voltage. I'll have to check it out when my car runs again (tonight!). I also plan on dynoing after the new motor is broken in, so I can verify the S-AFC readings vs. the wideband o2 readings.

Motor swapping is not all the fun it's cracked up to be Especially in a Neon

Urban Business

thermal

Too bad that this mod does not apply to VAFC.......

Jockobo

i tried that before and it makes my car run funny like the idle fluctuates a lot and sometimes the engine cuts off because it drops really low on the idle.

kpt4321

WRONG! The Factory O2 sensor is not NEARLY as accurate as a wideband O2 sensor. If you look here:

http://www.cmperformance.com/techinfo_oxygen.html

You will be able to see the difference in the curves of a normal and WB O2 sensor, with the axes representing output voltage and air/fuel ratio. The regular factory O2 sensor is the first type, which is designed to show stoich., lean, and rich, but it has no finer resolution than that.



This is NOT a good idea. When you tap the O2 sensor wire, you will effect the voltage, even you don't realize it, even if it may only be by a little bit. If you were to take a multitester, and read the voltage both before and after, you would see the discrepancy. This voltage drop will change the fuel trims within the ECU, and the car will not run with the air/fuel mixture it is supposed to.

Luckily, there is a way to fix this! A friend of mine has shown the proper method (he's an electrical engineer), and I mirrored it to here:

http://home.attbi.com/~tarryo/kyle/bluewiremod.html

All this does it take the input voltage (directly from the O2 sensor) and then outputs exactly that to the ECU and to the SAFC. That way, you are guaranteed to get the correct voltage.


Hope this Helps!

kpt4321

Bzzzz, wrong!

DSM'ers don't really care about O2's, at least the ones who know how to properly tune do not. Like I said in my above post, a regular O2 sensor is not very accurate at all, and does not do a whole lot for information.. It can vary depending on tons of other conditions, such as temperature, etc....

We all tune using fuel trims, knock sum, and timing advance. Much much better....

platinum00

why not just hook a volt metter up to the white wire from the sensor and get a reading that way. then you can still see the monitored items on your afc and still have the a/f , is there a reason this would not work

it's my understanding that all the afc is display the voltage from 0-1v.

platinum.

Blaze45

Could you just run a seperate 02 for this? Or does it have to be hooked up the to the ECU?

Blaze

ScottEK

I have a switch hooked up to switch to the O2 sensor on my VAFC, that way I can switch it back and not throw a code.

nigel

I kinda want an answer on the "can I just use a voltmeter to monitor?

ScottEK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Urban Business &raquo;</TD></TR><TR><TD CLASS="quote">
how to tune.
o2 voltages rage from 0 to 1. 0 being lean as hell and 1 being rich as hell
.500 - .600 volts corresponds to a stoichiometric (14.7:1) air fuel ratio. this is a dead nutz air fuel ratio. not rich not lean. anything higher than that correcponds to a more rich mixture. anything less than .500 volts translates to a lean mixture. anything over .600 trans lates to a more rich mixture. optimum performance during WOT is a slightly rich mixture.
</TD></TR></TABLE>

Why does thedropshop.tv say to tune to .90 - .92 volts?

xci_ed6

For the VAFC I am trying a new method.

I am going to hook the O2 into the TPS input. Then use the Throttle/RPM map to record a couple WOT runs adjusting both the high and low maps (set both to exact same thing) until perfect. Write down those settings and do a couple low throttle runs, adjusting both maps (set both to exact same thing) till close (the ECU can correct it by itself for low throttle). Then put the WOT maps back in the high throttle map. and hook the TPS input back to the TPS wire

I havn't tried this yet but I think it will work.

-Dustin

TravSi

i just hooked a digital volt meter to my o2 wire to see the readings...... .8 and up is rich anything below .8 is lean...because the vafc wont do the blue wire mod...but 17.99 for the volt meter at walmart isnt a bad price for a digital a/f guage.....works for me! and is very very accurate compared with wideband readings on dyno...i was almost dead nuts on the very first pull and had to make 1 small change.....

Trav

paz

no method using the standard o2 is going to be as accurate as a wideband o2.

also.....voltage wise this is how it should be-
you shoudl get a reading cycling between 250mv and 900mv. the average should be 450mv which would represent the perfect stoichiometric ratio.
that stuff is farily complicated.
if anyone is interested there is a very good thread on the g2ic board.
so tune your best to find a cycling in which the average is 450mv

ImAcracker

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by krustindumm &raquo;</TD></TR><TR><TD CLASS="quote">For the VAFC I am trying a new method.

I am going to hook the O2 into the TPS input. Then use the Throttle/RPM map to record a couple WOT runs adjusting both the high and low maps (set both to exact same thing) until perfect. Write down those settings and do a couple low throttle runs, adjusting both maps (set both to exact same thing) till close (the ECU can correct it by itself for low throttle). Then put the WOT maps back in the high throttle map. and hook the TPS input back to the TPS wire

I havn't tried this yet but I think it will work.

-Dustin</TD></TR></TABLE>
That sounds like a kick *** idea. I think Ill try it if I dont get a wideband first.

xci_ed6

better try it, I won't be. car is for sale and 200 miles away right now.

-Dustin