For technical electronics guys and smog gurus. Failing smog again. Happens every two years for me here in Ca.

New o2 sensor. Engine hot. ox1 runs between .800 volts and 1 volt at 2500 rpm. It doesn’t show any switching.

VF1 however under the same conditions does show switching. Open it sits around 2.25 volts and flops down to something less about every 4 seconds, which seems slow. Closed or shorted with the e1 te1 jumped it sits at 5v and jumps down to something less every 4 seconds. The fluctuations are very slow but I don’t know if that is my cheap meter or an actual problem.

Why is the ox1 reading static while the vf1 is not? What is this telling me?

At idle vf1 open is 2.25v, closed is 5v

 

Here's the manual page for diagnosing the O2 sensor. http://web.archive.org/web/201003261...01heatedox.pdf Note that you should run the engine at 2500rpm for a bit to assure the sensor is heated.

VF1 is conditioned (0-5v) Ox1 only when TE1 is grounded. When TE1 is open, it's Learned Fuel Trim, 0-5v in 5 steps (nominal 2.5v).

What were your last smog test numbers? This may help: http://www.cygnusx1.net/Media/Supra/...taTech/h56.pdf

 

Hi scope, thanks for the response. I have run the o2 test you linked to many times, I have the factory manual I am referencing. I can run the engine at 2500 for 5 minutes and it does not make a difference. The OX1 reading never switches or changes.

Before I get into smog details I am trying to find out why my ox1 reading does not switch while vf1 readings do. Is this normal? I don't understand exactly what you mean by VF1 being conditioned vs learned fuel trim.

 

Meaning, 5v but jumps down to something less every 4 seconds? Sorry, I don't know if that blip means anything. Sure sounds like you're running way rich. Can I assume you failed smog with very high HC?

 

Sorry if I didn't explain clearly. What I am trying to say is that when we are checking to see if the o2 sensor is working or switching back and forth and working properly we are looking for a swing in voltage correct? Ox1 does not swing or change at all while Vf1 does. Is that normal?

My mechanic is saying that my o2 sensor is pegged rich at 1 volt and not moving or changing when measured at ox1.

Last smog failed at 15 and 25mph for High HC, it also failed NO at 15mph.

I definitely want to get into the smog part of this but I really want to understand the Ox1 and Vf1 readings first.

 

I agree with your mechanic; the O2 sensor is indicating too rich.

Vf is only conditioned Ox1 when TE1 is grounded. If I understand your post correctly, it then blips down "some" about every 4 seconds. I don't know why it is doing that, but since "almost all" of the time it is 5v, it's "agreeing" with Ox1.

You could use a 5-gas analyzer to confirm that you are too rich, but since you already have the smog test results, and your new O2 sensor is saying "too rich," and the ECU seems to be agreeing, I'd start my diagnosis trying to figure out why you are too rich. (The first thing I would look at is a miss. You can put the inductive pickup of your timing light on each plug wire; the one that seems erratic is probably missing.)

 

I agree it is rich. I'm sorry, I don't mean to keep asking the same question and I am not trying to be a pain but I think I am missing something and just trying to understand. I am not very electrically savvy so bear with me.

In the FSM you referenced where you ground TE1 and read a "conditioned" o2 reading. The manual says "Check the number of times the voltmeter needle fluctuates in 10 seconds" and it should be at least 8 times. Mine fluctuates 2 times in 10 seconds. Per the manual I should change the o2 sensor which I already did. So this is where I am stuck in this cycle where it just keeps coming back to "replace the o2 sensor". Now we know its Rich, does it being Rich not allow its voltage signal to fluctuate the way the manual suggests it should? A yes here would explain a lot to me in my head. Otherwise why is it not fluctuating 8 times like the manual says.

If we assume everything is working perfectly like a brand new off the showroom 4runner back in 1993.

At 2500 rpm:
1, VF1 should read what when grounded?
2 What should OX1 voltage read?
3 Should OX1 voltage fluctuate the same amount of times as VF1?

I really appreciate your input.

 

Don't ground VF1.

Ox1 is the straight output from the O2 sensor. It is telling you, almost certainly truthfully, that you are TOO rich. While I, too, would expect Vf1 to be stuck at 5v with TE1 grounded, I can't explain why it "jumps down to something less every 4 seconds." It certainly doesn't suggest to me that there is any problem with the O2 sensor.

So I'm pretty sure (as your mechanic was) that you have no problem with your sensor. Your problem is that your engine is running too rich. That is why you are failing with high HC. (It doesn't explain the high NOx, which is most likely a separate EGR problem.)

I would expect that once you get your exhaust within range, the Vf1 signal (with TE1 grounded) will fluctuate pretty much in time with Ox1. But since Ox1 is completely pegged, I wouldn't worry yet about Vf1.

After all this, I wonder why you didn't mention codes. You seem savvy enough to have checked there first. With a pegged O2 sensor, I would expect 26 (and probably 71).

 

I am mechanical savvy but not with electronics. I will start going throw the systems again to figure out why I am rich.

I have never had any codes ever since I rebuilt the motor 6 years ago but it has failed smog every time. And yes the check engine light does function and I have tested it.

I will post up my last three smog tries when I get inside and what I did in between each one. The results are all over the place.

 

Smog 1


After smog 1 I replaced my catalytic converter which was damaged from off-roading per my mechanics advice.

Smog 2



After smog 2 I think my mechanic was scratching his head as to why everything went to ˟˟˟˟. He did a smoke test and found I had multiple leaks around the egr and all around the cat and o2 sensor. So I pulled the exhaust from the cat back and re-welded everything and installed a new o2 sensor and gasket. I have welded many times on my vehicle and he was concerned it did something to the sensor because I have never disconnected the battery. I also made some custom bushings to seal out the egr connections to my header(smog legal). I checked the basic function of the egr by applying vaccum and the engine dies.

Smog 3



After smog three he checked the ox1 port again and found it showing full rich. He had checked this previously along with all the other sensors that one would check and this was a new issue.

So since the first smog
new cat
new o2
new plugs, cap, rotor
new TPS
Plug wires replaced 20k miles ago with factory toyota

This engine is not stock and though I have smog issues every time it has passed with a little tinkering.

I have Doug Thorley headers and upgraded fuel injectors that I was told would flow well within the computers capability. My cylinder heads have had considerable port work.

So with all this. If I can’t find something wrong then I will slowly start working on putting everything back to stock.

 

A few random questions and observations: (I wrote these to you privately, but thought I'd mention them here as well. Scope has covered most of this.)
- An O2 sensor stuck high (.9V) indicates the engine is running rich (all the O2 in the exhaust has been being burned up).
- When you say "Vf1 closed" or "Vf1 open" I assume you're talking about TE1 being shorted or open. VF1 is an output and should never be shorted to anything.
- The fact that VF1 shows 2.25 volts with TE1 open (I assume) indicates the ECU thinks the engine mixture is more or less correct, so that doesn't correlate with the O2 reading.
- How fast is VF1 cycling with TE1 shorted? It should be about once/second, from 0V to 5V and back.
- What kind of meter are you using to measure the O2 sensor? The sensor is very high impedance and won't measure correctly with a cheap analog meter. A digital multimeter should give you usable readings.

 

Yes, my bad, I meant grounding or jumping TE1

This also was confusing to me but I don't know what the heck I am doing.

It is very slow, about once every 3-4 seconds. This is a concern of mine especially since my mechanic is worried about frying electronics while welding on my vehicle which I have done a ton.

I am using a Home depot $40 digital meter. The specs say >10Mega ohms and has a sample rate of 3 times per second.

 

Print the OX sensor diagnostics pages (197-198?), pencil in your test results and use a highlight pen to chart your path through the flow chart.. You might find it helpful in explaining where you're at in the process.