out with the old, in with the, well, old... (6 Viewers)

[CreeperSleeper]

the visors are perfect with labels intact.

Your Mom is perfect with the labels intact...


Seriously, the Runner looked amazing. It makes me kinda sad that I have to give mine up... Very well done and it was good meeting you.

 

[2ndGenToyotaFan]

I'm so stealing that hood the first chance I get!

 

[gnob]

so the runner made it back in one piece.
nothing broke or fell off. the only code thrown in 250 miles is the po420 cat efficiency code.

thanks to jerod, i think i have a trans that works in all gears, just need time to swap.

so here are a few mcgrew pics that turned out good.

 

[2ndGenToyotaFan]

That thing is a monster! Full-on raging jealousy right here!

 

[gnob]

went ahead and made an o2 bypass from this link O2 sensor bypass

uses a 1 micro farad capasitor and a 1/2 watt 1 megaohm resistor in parallel.

appears to me that it is making the ECU actually not look for a second sensor.

the scan tool never showed a voltage for the second sensor, i ran a three trip drive and couldnt get a light yet. as much as i hate the light on, the po 420 code always amuses me.

on the truck, i unpinned the truck side of the sensor wires, connected to the terminals on the bypass, then heatshrinked over the connection. should be golden

Radio Shack part #
1 micro farad cap 272-1055
1 mega ohm resistors 271-1134

heres a couple pics

 

[2ndGenToyotaFan]

I don't know what you just said.... but it must be awesome if you bothered to take pics of it!

 

[Kief]

What- no 12 ohm resistor? did I miss that?

It looks like you just mimic a happy sensor basically?

I need to check my engine light code.. I am not spending $$$ on an O2 sensor.

 

[Ebag333]

I need to check my engine light code.. I am not spending $$$ on an O2 sensor.

On which truck? If it's the 80 series, the ECU actually uses it to adjust fuel trim.

 

[gnob]

no, the 12 ohm is for the heater side of the circuit. i left that in tact.

this mod is just for the secondary sensor, it is like i said, either making the ecu not look for it, or is providing a "good" signal to the ecu.

however, it wasnt showing voltage on the scan tool, so i think its kind of a delete.
i am going to put some more miles on the truck today and see what happens.


also just to be clear. the post cat o2 is NEVER used for fuel trim.
it cannot be used in that manner because the cat changes the chemistry of the gases going through it.

 

[Ebag333]

also just to be clear. the post cat o2 is NEVER used for fuel trim.
it cannot be used in that manner because the cat changes the chemistry of the gases going through it.

That's not my understanding of it, but everything I've read is 80 specific which may be different.

Rear O2 sensors monitor the ecu corrrection of STFT, LTFT and catalytic efficiency. In the 80 OBDII Toyota also uses the rear O2 signal input to trim Baseline Fuel Values by about 2%. This is minimal, and common to account for reduced catalyst efficiency over the life of the cat.

Yeah it's Sumotoy, but I've seen that referenced elsewhere by multiple sources (and in Toyota's technical docs for the 80 series).

Also IIRC Kief's 80 series are OBD-I, which means they have the left/right bank O2 setup, both pre-cat, rather than the pre/post cat setup of the OBD-II trucks.

 

[gnob]

with all due respect.

it is checking cat efficiency, which in a round about way is looking at the primary fuel adjustments.

for the sake of argument, if you go away from a toyota cat, or to a newly designed toyota cat. then its going to shoot the whole argument out of the water. i think what people dont really realize is the regular o2 sensors have a VERY limited line of sight. they are reading from about 14.6 to 14.8 ish.

so i think that any literature stating that the rear cat is doing anything other than giving the ecu a viewing window, is either wrong or has been misinterpreted.

 

[Ebag333]

with all due respect.

it is checking cat efficiency, which in a round about way is looking at the primary fuel adjustments.

for the sake of argument, if you go away from a toyota cat, or to a newly designed toyota cat. then its going to shoot the whole argument out of the water. i think what people dont really realize is the regular o2 sensors have a VERY limited line of sight. they are reading from about 14.6 to 14.8 ish.

so i think that any literature stating that the rear cat is doing anything other than giving the ecu a viewing window, is either wrong or has been misinterpreted.

I think a lot of it depends on if you're talking about the old narrow band, or the new wide band O2 sensors. I agree that the narrow band is a very limited look into the system, especially compared to wide bands.

I also agree that the primary job is for cat efficiency.

Obviously Mr. T has a way of disabling the rear O2 sensor, as many overseas trucks do not run them. The big question would be if that's a simple disable (such as what you've done) or requires an ECU change (in the 80 series overseas trucks do run a different ECU) to be done "correctly." I know of several cases where people have replaced their rear O2 sensor and corrected a rich or lean running condition, not all of those situations had the O2 throwing codes. For pre-OBD-II, fooling the post-cat sensor shouldn't be a big deal at all. Post OBD-II...maybe more of an issue.

Running with the ECU fooled for the rear O2 is not likely to cause any significant problems, to me it seems more of a last line of defense for the ECU. Say there's a lean condition (caused by a vacuum leak, front O2 sensor not operating properly, etc), then the rear O2 can catch that and correct it (a small amount). The amount of correct the rear O2 does seems to be small, but at least in the 80 series it does seem to have an effect.

I know that I'm running rich right now. I did not understand why my fuel mileage dropped by about 2 MPG, finally figured it out a 6 months later when the rear O2 sensor finally failed enough to throw a code (and I put two and two together). Which is somewhat frustrating as I replaced/checked a lot of other parts trying to track it down. Oh well, at least I have a bunch of other new parts on the truck.....


(All the above is for the 80 series. I'll bow to your expertise on other vehicles. )

 

[CreeperSleeper]

gnob's correct. The second O2 sensor (even on my 80) is just making sure the cat is doing what it is supposed to. All of the fueling adjustments are the pre-cat O2 sensor. I haven't been running a post-cat O2 sensor on my 80 for 3 or 4 years.

 

[gnob]

i think what your missing gabe is that a cat is not always going to mix the gas the same.
sometimes its bonding every oxygen molecule to every carbon monoxide molecule.
sometimes its bonding every other molecule.

to play devils advocate, i can see it being used as a secondary eye if the ECU KNOWS the front sensor is failing. the front sensor is monitored with some sort of algorithm based on load, temp, pulse width etc.

so if for some reason the ecu is using problem X+Y+Z=xyz
and its seeing X+Y+Z= xxy

it may look elsewhere, but in most cases its going to fuel trim out and throw a light

 

[2ndGenToyotaFan]

Soooooo....... is the CEL on or not?

 

[gnob]

no light so far, went to medford and back today.
i have prob close to 60 miles without the lite yet.

i do show the other readiness tests arent completing though, per the scan tool.
the o2, cat, and evap are not completed. so in a real smogging situation this could be a concern.

 

[D3fiant]

I think the CEL mileage to turn on for toyotas for your 3.4 is 25 miles IIRC. so you should be good

Secondary O2 is only to let the ECU know that the cat is working correctly. thats all it does.

I actually smogged back in december in my 96 OBD2 80 and passed even though with a scan tool it said "not ready" when they plugged into my port it even said not ready on his screen but the 80 passed the test anyways. maybe I just got lucky not sure.

 

[Ebag333]

I actually smogged back in december in my 96 OBD2 80 and passed even though with a scan tool it said "not ready" when they plugged into my port it even said not ready on his screen but the 80 passed the test anyways. maybe I just got lucky not sure.

Oregon allows one or two not ready codes (two IIRC). It's better to reset the ECU and get tested with not ready codes, then to get tested with a failed code. If you do not pass with a failed EGR or O2 code, then you have to be in a ready/good status in order to pass. (Ask me how I know.... )

 

[D3fiant]

thats good info to know, i"ll have to remember that.

 

[gnob]

i finally got around to getting the tranny swapped. started yesterday morn with pulling the trans/cases.

had to lower the truck because the jack didnt reach, didnt feel like wrestling the tires to swap to the skinnys

made a makeshift "path"