some drunk guy

1991 4runner 3.0 5 speed.
Runs great. (as far as I can tell, Ill try to be as descriptive as I can)
NO Check Engine lights, but yet Failed smog miserably in California, running Rich.

So , I did a New O2 sensor, swapped out AFMeter with another factory one I have on another 4runner
I adjusted the TPS to spec, and set timing at 10*btdc
Installed a New Water Temp sensor, and..
OH and a brand New CAT

Smog results are: HC max 62 Measures 184 CO% max 0.45 measures 1.49 NO max 356 Measures 3 FAILED for HC and CO

So Ive been pulling my hair out this last week trying to chase down the issue. I did a compression test to rule out bad valves and I have 155+ across all 6

I read an older thread about running open circut but it was alittle vague in details, and no solution.

So my question is I may have some faulty wiring, ON the diagnostic port, I dont have any reading on the OX1 , or I should say it reads 0.0

on VF1 I read. .12

If Im reading 0 on the ox1 port and I believe Im supposed to be reading .1-.9v, what wire is that? Or any other suggestions.??

Scope you have always helped me in the past, any thoughts?

scope103

"Open loop" Open circuit is something else.

Yeah, Ox1 should go directly to the O2 sensor. If you're getting 0.0v to ground, I would suspect a wiring issue. Start by "ohming out" Ox1 to the black wire on the O2 sensor plug (you should have Blk, Gr-B, Br, and W-R) A disconnected O2 sensor would definitely fail you. (Hmmm. Maybe that's what you meant by open circuit ...) (You should get about 0.1 swapping back and forth with 0.9, 8 times in 10 seconds. But the sensor has to be heated up to do that. You have a heater in the sensor for just that purpose, and a failure of the heater should throw a code.)

BUT, I can't understand why, then, you're not getting a code. So actually check it; you need to see that 2/second flash on the combination meter. (And, you could have a stored code, but the smog check is supposed to pick that up.)

High HC and CO can be caused by misfire. While you ought to be able to hear it, you could try propping open the throttle to get it to run about 2000 rpm, then pull the plug wires one at a time. If the rpm doesn't drop as much on one, it may not be firing.

some drunk guy

Scope thanks for the reply, so from OX1 port on diagnose box, to black wire to O2 sensor I get 1.7 ohm.

some drunk guy

but with the truck running, I get 0 voltage at OX1

some drunk guy

Just more info,.. As per FSM trouble shooting flow chart for Inspection of O2 sensor..

The brand New O2 sensor registers a Resistance of 5.2 (so its with in spec)

Next it tells me to warm up the engine and connect via Voltmeter VF1 to E1 on the Diagnose port
Check
It also says to put in diagnose mode via TE1 and E1
Check

The FSM doesnt say anthing about testing the Ox1 port?

scope103

Vf is "conditioned" Ox1; it's after it went through the amplification circuitry. It should swap back and forth in time with Ox1, but going from 0v to about 5v (the FSM accepts anything "more than zero:") http://web.archive.org/web/201503060...42oxygense.pdf

But you're not even getting Ox1. You could have a completely bad O2 sensor (not too likely). Maybe you have a broken ground wire? (BR. W-R is B+ for the heater, and Gr-B is grounded by the ECU to turn the heater on.) Check BR to ground would be easy enough.

Next you could try checking the O2 sensor, but this will be harder. It's a voltage source; it will put out voltage even with the it disconnected from the truck harness. But it has to be hot. So you'd need to hook it up to a voltmeter and then you'd race the engine for 30 seconds to make sure it's hot enough. Since the engine will be in Open Loop the signal from the sensor won't flip, but you should be able to get at least 0.1 v (and at most 0.9v).

Just to ask the obvious question, are you sure your in a voltage range that will distinguish 0.0 from 0.1? If you're in the 199 volt range, you have no decimal digits.

some drunk guy

Ill check back on it tomorrow morning for the ground signal at the O2 plug connector.

The o2 sensor is brand new, (I know means nothing but) it ohms in spec.

When TE1 /E1 is connected, and then I use my volteter to measure VF -E1 at Idle I get 0.1v and then at 2500rpm I get 5.1v. At idle back down to 0.1v, but I have yet to see any fluctuation in numbers , and still 0.0 reading at OX1

Hmm, Ill check ground and report back

some drunk guy

Also, if im getting 1.7ohm at OX1 port to Black wire at O2 plug connector, does that mean the black wire is good?

scope103

The ohms test on the sensor just checks the heater; it doesn't have anything to do with the sensor. But I'm really skeptical of claims that new parts are bad out of the box. Particularly when 1/2 (the heater) is good.

1.7ohms is close enough to 0 ohms. Your test leads by themselves are probably close to 0.7, and who knows how good your connection to the wire was.

But if you get "zero" on Vf at idle and 5v at 2500rpm, that sounds like it is working (putting Ox1 aside for now). If I understand this page correctly, http://web.archive.org/web/201003261...01heatedox.pdf
0v is "rich" and 5v is "lean." (on the O2 sensor, 0.1v is lean, and 0.9v is rich). This could be lots of things (a leaky injector, leading to too rich at idle but overwhelmed at 2500rpm)

Have you checked for stored codes? This could help a lot.

some drunk guy

Scope, when I first fired it up I was getting code 22, I replaced the water temp sensor, and still was getting code 22, I ran new wires from a donor harness, with a good connector plug and wires directly to wires at ecm plug, cut about 2' away from plug and soldered the connections, No more code 22 , and after about 30 miles, no more stored codes. (thats the most frustrating part, I have no Idea where to start next)


Just to recap my wire colors are different at O2 sensor being a 1991
I have
-Black shielded wire
-Brown
-Pink with green
-White with Red

Testing with my power probe,With the Ign on and off, I defiantly have ground signal on the Brown wire a the O2 sensor plug under the truck.
With Ign on I have 12v power at white/red,
With Ign on I have 3.3v on Pink with green
With Ign on I have a ground signal on black?

Other things to mention, that I forgot, it has a hard time starting when cold or first startup of the day
-some of the brown wires at the ecm seem like they are ground powered by ecm and lose ground with Ign is off? (water temp sensor for example)
Do they need a true constant ground?

some drunk guy

Update: I repaired the plug connector at the O2 sensor.Old one was questionable.
Now I get the same reading on OX1 as VF1 which is basically 5v to .1v

Im still wondering if I have my test set up correct?

With TE1 and E1 jumped, With my Volt meter in the Volts position, I put my red lead on VF1 and black lead on E1 I get the reading. Is that correct?
With the Red lead on VF1 and I move the Black lead to OX1, I get the same reading, is that correct?
Not sure how to connect what to what to correctly read the fluctuation in 10 seconds that the fsm talks about..??

scope103

Ow.

The direct output of the O2 sensor is about 0.1v when there is oxygen in the exhaust, which flips (pretty quickly) to about 0.9v when there is no oxygen in the exhaust. That is what you should see on Ox1. But all these "abouts" are hard for digital circuitry to think about, so the first thing the ECU does is convert anything under 0.5v to 5v, and anything over to 0v. That's what you see on Vf. They should NOT be the same.

Your test setup is correct; E1 is ground so you can read either Vf or Ox1 to E1.

So what's (supposed to be) going on? The ECU wants to set the amount of fuel (by setting the injector on-time) to exactly the right amount, so that all the fuel and all the oxygen are burned up. It can measure (in a yes/no fashion) the oxygen in the exhaust, but it has no way to tell (once all the oxygen is gone) if there is fuel left in the exhaust. So what the ECU does is constantly shift the amount of fuel back and forth; it adds fuel until the oxygen is gone, then backs it up until the oxygen just starts to reappear. (If you know how to sail, this will sound familiar.) It does this "about" 8 times in 10 seconds, so both Vf and Ox1 should be shifting back and forth (between their own respective voltages) 8 times in 10 seconds.

If either Vf or Ox1 are stuck on one side, that means the ECU is doing it's best but can't get the mixture right. For instance, if you have a big vacuum leak (adding much more oxygen than expected), the ECU just can't add enough fuel to get the O2 sensor to say "okay, now the oxygen is gone." Then the ECU throws code 25.

So what is puzzling me is how you can get such obviously bad numbers on Vf and Ox1, WITHOUT a code.

some drunk guy

Correct No stored codes.

So I just again , did the FSM test, same as in the link you sent.

1)Warmed up the engine for 90 seconds at 2500 rpm.
2)connected Te1 and E1 with sst (piece of wire)
3)check number of times Volt meter fluctuates in 10 seconds from VF1 to E1....0 times
4)repeat.....0 times
5) Read Diagnostic codes....NO Codes
6)Remove SST from Te1 and E1
7)Measure Voltage Vf and E1 I get .....0.10 V
8)Replace O2 sensor...(the one I just bought, I called to warrenty it out, So Ill go pickup the replacement tommow and report

some drunk guy

I replaced the O2 sensor again. SAME RESULT. Soo frustrating, I just want to run this 4runner off the cliff. LOL

Its running rich, No way around that. Im still not getting any codes, and honestly if it wastn for failing the smog test, I would have no clue because the 4runner rips.

I may try to Modify the AFM to move as Much air as possible and try and Lean it out.

Any other suggestions?