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Discussion Starter #1
Car threw a code 26 a while back, went away after I changed the air filter. However it came back randomly while accelerating on to the freeway. If the car is running rich would just disconnecting battery "reset" and allow the ecu to normalize again? Also since the o2 sensor is a possible cause, does it mean a fault in the sensor, or could a bad wire cause it? I haven't thrown a code since I replaced the secondary o2 sensor so I'm thinking it might be that but I'm not sure.
But, I'm not sure if code 26 is referring to the sub or main o2 sensor since I have a California car.
 

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Secondary downstream O2-sensor makes zero contribution to air-fuel ratio, it's only there to monitor catalytic efficiency. Don't get cause & effect mixed up. The code and failed smog is just result of problems, fix those problems and the results will change. Clearing code is just sweeping things under rug, problems are still there and code will come back. You've got many problems:


1. fix your MIL light-bulb. Should light up when key is ON before cranking

2. fix your idle-speed, could be vacuum-leaks and/or idle-valve. Measure intake-manifold vacuum with warmed-up engine

3. check and measure your TPS. Make sure angles are correct and idle-switch working correctly. Otherwise, it'll send ECU wrong data and ECU will look up incorrect fuel & ignition values

4. Adjust your ignition-timing when engine's idling correctly. In CA, you're allowed +/- 3-degrees from number listed on bonnet decal.

5. test upstream O2-sensor output waveform. Need to determine if O2-sensor is sending correct data or if it's defective. If it's sending correct data, then you've got even more problems to deal with.

6. measure vacuum at FPR nipple (use vacuum-T). This control fuel-pressure in rail and is primary contributor to fuel-volumes being injected.

7. measure fuel-rail pressure with vacuum hose to FPR connected and disconnected. What are these two pressure readings?

8. measure vacuum at EGR valve when engine's revved above 3000rpms. Test EGR valve by applying vacuum to it. Does it stall engine? Two possible problems here, bad valve or no vacuum going to it.


If anything, smog-test data shows you're running LEAN due to high NOx. Or have too much ignition-advance. Or EGR system is faulty.
 

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Discussion Starter #4 (Edited)
Secondary downstream O2-sensor makes zero contribution to air-fuel ratio, it's only there to monitor catalytic efficiency. Don't get cause & effect mixed up. The code and failed smog is just result of problems, fix those problems and the results will change. Clearing code is just sweeping things under rug, problems are still there and code will come back. You've got many problems:


1. fix your MIL light-bulb. Should light up when key is ON before cranking

2. fix your idle-speed, could be vacuum-leaks and/or idle-valve. Measure intake-manifold vacuum with warmed-up engine

3. check and measure your TPS. Make sure angles are correct and idle-switch working correctly. Otherwise, it'll send ECU wrong data and ECU will look up incorrect fuel & ignition values

4. Adjust your ignition-timing when engine's idling correctly. In CA, you're allowed +/- 3-degrees from number listed on bonnet decal.

5. test upstream O2-sensor output waveform. Need to determine if O2-sensor is sending correct data or if it's defective. If it's sending correct data, then you've got even more problems to deal with.

6. measure vacuum at FPR nipple (use vacuum-T). This control fuel-pressure in rail and is primary contributor to fuel-volumes being injected.

7. measure fuel-rail pressure with vacuum hose to FPR connected and disconnected. What are these two pressure readings?

8. measure vacuum at EGR valve when engine's revved above 3000rpms. Test EGR valve by applying vacuum to it. Does it stall engine? Two possible problems here, bad valve or no vacuum going to it.


If anything, smog-test data shows you're running LEAN due to high NOx. Or have too much ignition-advance. Or EGR system is faulty.
What is a proper idle speed? I've read it's normal for the car to idle at around 600-700.
I'll have to check vacuum related stuff when I find vacuum guage though..
As for the egr valve, it actually just got replaced yesterday since it broke. The ignition timing should be fine too since it was recently serviced maybe a month or two ago (10° btdc when I recently checked).
Also, when smogging the older obd1 cars do you have to have the te1 and e1 terminals jumped? (I'm assuming it's the same procedure all the time)

Thanks for the in depth write up.
I'll update with the various readings and such at some point hopefully.
 

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Discussion Starter #5 (Edited)
-Tiny update- checked o2 sensor readings, giving a constant .1v reading. So I probably have to wait until I find my vacuum guage before further testing/ retesting? Since .1v is indicating a lean mix? Though I thought the range in the repair guide said .4v to .6v
 

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Was car fully warmed up? Takes about 5-10 minutes for engine to warm up and for O2-sensor to start working.

Really need oscilloscope to plot waveform. Should swing between 0.85 to 0.10v and do at least 8 cycles in 10-seconds.



Might be possible to monitor this with analogue voltmeter and count the needle swings.
 

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Discussion Starter #7
I idled the car for about 2-3 minutes then held the rpm at about 1600-2000 for 2 minutes before checking. I'm probably going to retest tomorrow though.

As far as equipment I only have a multimeter (Fluke 21 series ii I think). I'd been using it on the DC setting (following the Chilton's/ Haynes procedure for checking).
 

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The ignition timing failed because the idle speed was wrong, not because the timing itself was set wrong. There is a sticker in the engine bay that tells you how to set/test the ignition timing and the tech has to follow those conditions. Also, make sure when you set the timing that the jumper is set in the check connector in the engine bay.

Otherwise, the smog results show high NO readings, which points to a problem in the EGR system.

Code 26 could be a problem with the main or sub oxygen sensor, or an actual problem with the motor (leaking cold start injector, etc.).

-Charlie
 

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Discussion Starter #9 (Edited)
Ok thanks for the response Charlie.

For the idle speed not being correct I'm still a tad bit unclear on where the issue, other than the idle speed being wrong. My car idles at 6-700 rpm when in gear at a stop unless the a/c is on then it's at ~1200 and when in nuetral/ park it idles at around 8-900rpm. I personally did not end up taking the car for smog it was another family member so I have no clue if the tech was being careless in some form but I doubt that's it.

I just replaced the egr valve since it ended up breaking unfortunately..

As for the O2 sensors I'm going to recheck them after I finally get around to checking various vacuum readings (finally found the guage, a 1987 snap-on guage though!). However, is it ok to test the O2 sensor when it's not plugged in (connect multimeter to sensor plug and battery ground), I saw a few videos/ demos doing it this way, and I can't get a good back probe so it seems much easier

Tiny update, I only got around to checking intake manifold vacuum, which im not too sure if I did right but the reading was 20in. I don't have a t fitting and I'm not too sure how to check the other areas brought up. (First time using the vacuum gauge lol!)

Another small update, rechecked the o2 sensor after driving around running errands and it gave me .5v to .6v flux every few seconds then it dropped down to .1v which I'm thinking isnt right? Maybe I'm just testing it wrong lol..
 

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There is an "O2" connection in the diagnostic port - use that with the multimeter to get the voltage on the multimeter. That way, it can be left plugged in. The "Vf" pin will tell you the fuel trim that the ECU is applying to the motor at the current rpm/load (2.5V = no trim, lower or higher 0-5V = richer or leaner, though I can't remember which way is which).

I believe the idle should be right around 700-750 in Park/Neutral. The acceptable range will also be on the sticker.

You can adjust the idle RPM with AC on by turning the large screw on the AC bypass valve (opposite end of the manifold from the throttle body). You want it around 900-1000 in gear at idle. I adjusted my (manual transmission) to idle around 1000rpm with AC on, my non-adjustable 3s-gte is in the 900-1000 range with AC on. That's not an issue for the smog check though...

~20 in of vacuum is about right, but you could still have a small vacuum leak or something causing a problem that won't show up with a vacuum gauge.

-Charlie
 

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Discussion Starter #11 (Edited)
Wait what, really? Dang it that would've saved me some time LOL. I'll recheck everything again once I drive around again sometime. Do I still ground to battery terminal when testing the O2 port and vf? Not sure which ports to use either for vf, 1 or 2? I'm assuming the o2 sensor upstream is oxy1 though.

My car is idling at 900 steady now in park with no ac. Not sure why, it honestly is usually about 6-7 or was before. With AC in park it's about 1200 still. In gear I'm at about 500-600 idle no ac and 1000 with ac.

As for leaks I looked at ever line/ hose I could get to and felt the ones I couldn't see but that might not be enough if it's a small leak? But as far as I can tell it seems fine. Hoses look like they were changed not too long ago as well (sometime before I got the car). The only area I can think of would be the pcv but I thought people vented those to the atmosphere sometimes so I'm not sure it would be a problem.

Small update, went to the dlc1 port and I'm assuming I'm checking e1 & ox1 and e1 & vf1. Readings were .06v and 3.6v respectively.
 

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Discussion Starter #12
Tested the O2 sensor after I replaced it (wire broke on old one..) it was going between .5 and .4 ish slowly at idle so not sure what else.

Vf1 read at 3.5 at idle and it goes to 2.5v with ac, so guessing in gear it's different vs idle.

Adjusted idle speed to 750 for the time being until I test for vacuum leaks.
What's the preferred method for finding vacuum leaks? Propane? I dug up some old propane from camping supplies so I might try it tomorrow.

Fixed an apparent exhaust leak on the manifold due to a broken stud and put a fuel cleaner in the gas for good measure.
So

Overall got a few things done at least. Not sure what else I should be checking for after vacuum leaks.
 

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Fixed an apparent exhaust leak on the manifold due to a broken stud
Exhaust manifold leaks can lead to incorrect readings at the O2 sensors... so this is a good part of the fix, hopefully. The exhaust pulses leak out and also suck fresh air back in to the exhaust (depending on exhaust pulsing) - the fresh air reads on the O2 sensor as no enough fuel and more gets dumped in the engine (that would explain engine rich codes).

-Charlie
 

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Discussion Starter #14
Well after each small fix Im clearing the codes to try and see so hopefully this time after a few drove cycles they stay off. Still going to have to check for vac leaks though.
 

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Discussion Starter #15 (Edited)
Shot propane over every vacuum line and nothing happened so I'm going to guess that I should be okay as far as vacuum leaks go.
So it the light comes back on I'm going to be at a loss haha.

The car feels a bit bogged down but I think that's my fuel filter since I just ran a cleaner through and the filter is pretty old.
Not sure if it matters but I have an a/t.

Anyways
Thanks for all the help y'all.
 

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Good job! Hopefully all that fixed the problems.

Way I like to test for leaks is to plug exhaust pipe. Then pressurize intake to 2-3psi. Then squirt soapy water at all joints and clamps of intake-tract all way to block. Bubbles fizz out where there's leak.
 

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Discussion Starter #17
Hopefully! Just made my weekly commute to Pasadena and back so hopefully I'm good for now.

As for the air I might try that since I at least have an air compressor haha.
 

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Discussion Starter #19
Pasadena and the surrounding cities seem to be a hot spot for Toyotas. Ive seen more gen 1s in Pasadena, Arcadia, and rosemead than anywhere else! Could've just been luck though haha.
Nice area over there, Pasadena has a small robot comics convention bi-annually too. Fun place
 

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I make near daily trips to Pasadena! Or, rather, out of Pasadena. :grin:

-Charlie
 
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