abecedarian

Something to keep in mind is how the ECU determines when to throw a code for emissions related things. Code 25 is thrown after 90 seconds has passed and the O2 output voltage has been less than 0.45 volts during those 90 seconds. Besides the possibility of your mixture actually being lean, it can also be caused by a faulty O2 sensor, or by the heater circuit in the O2. If the heater circuit is not getting proper voltage from the ECU, the O2 sensor won't work properly and can cause a false lean trouble code. Since you're not getting a code 21, I wouldn't suspect the sensor not getting voltage, but I can't rule out excessive resistance in the circuit. Solution: check for 12V at the plug to the O2, on what I remember being the black and brown wires in the plug... I think the other two, pink/green and white/red are the actual O2 signal.... Having a brain fart.

A couple other things you can check:
- Exhaust leaks-
- - these can allow air to enter the exhaust and cause a false "lean" condition.-
Vacuum leaks in the intake or broken, cracked or otherwise damaged boots in the intake between the throttle and air flow meter / air filter housing-
- - these can allow unmetered air into the system and lean the mixture.
- Fuel filter-
- - this can cause low fuel pressure in the fuel rail, and thus not enough fuel being injected.

EGR could be a problem too.

But with over 100K miles on it, I would be willing to bet the catalytic converter is failing. These are a 3-way converter and can produce passing HC and CO2 results and fail NOx.
Magnaflow has a good offering and they're only around 250 or so installed.

ChefYota4x4

iTrader: (5)

^^^^ ..........

My 2 year old CATCO cat failed, no doubt.(I think I have other issues CAUSING it to die maybe 30% sooner... but I've been told they're junk by most exhaust guys.. Including the one who installed my Magnaflow for 225$/along with some other stuff he did). Seeing as you are SO CLOSE, Lankan.... it might very well be PART of what's going on(surely you would pass the sniff with a new CAT...BUT, would that eliminate the code?)

Lankan

ChefYota4x4, I did not test the coolant temperature sensor across the whole temperature band. There's an acceptable range shown in the FSM, and at the temperature I tested (taken by a thermocouple I touched against the CTS housing) it read 120*F. At that temperature, the resistance I read (.68) was right on the money! About installing a new cat... as you say, it may pass, but I'm sure it won't take care of it spitting out code 25.

abecedarian, I have checked for vacuum leaks and found none, and also installed a fuel filter prior to my 2nd test. I'm going to look into this heater circuit in the O2. Can anyone point me in the right direction? In the mean time I will check for 12V on the plug to the O2. I DO have a leaking muffler (which is right after the cat). Can this be what's causing the issue?? Another possibility just popped into my head... my truck originally came with 225x75x15 and it now has 31x10.5x15. Knowing that I'm passing the 25mph test with no problem (higher rpm), is there a possibility that I'm failing the 15mph test because of the lower engine rpm due to the larger tires??

Soul_keeper

My truck just failed smog today in CA

they said it's running too rich ...
CO(%) was high

ChefYota4x4

iTrader: (5)

Ahhh, ok, gotcha! I would start a 'repeating P.O.E.(Process-Of-Elimination) that you post each post as you eliminate stuff, even if it's b4/after the post of your findings each time.

Ie;

* List all the things the FSM is saying you could be having a problem with...

* Then, post the answers in red, thereafter each line...

* Then explain what/how you tested and the findings...

It keeps NEW VISITORS(especially the Smog-Guru's) from having to read back at all. You could even use "QUOTE" and enhance it each time from the original... That way it would be clear its YOU quoting YOU, lol.

************************************************** **********

Far as the Heated 02... I KNOW there's a section for troubleshooting codes in 3 different sections of the FSM... HAS to be the full P.O.E. in at least 2 of them for the 02(or 2 different test procedures for the 02 in 2 places).

* Has to be a test for that heated circuit AT the ECU and AT the connector... It's in there, keep fishing, you'll find it

abecedarian

Lankan- yeah, the code 25 is something to deal with. That is a direct code from the ECU saying for whatever reason, you're running lean. The lean condition would likely contribute to your fail of NOx tests, and considering the cause could reflect why NOx gets better at higher RPMs.

One or two cylinders running rich could cause the other cylinders to lean out since the O2 reads all cylinders' emissions added together. As a "group", this could make the O2 see lean.

Pull your spark plugs and look for plugs that don't look like the rest: i.e. some have reddish to white "ash" like deposits and others are dark brown to black to even looking wet.

There's a chance that new plugs and maybe new ignition coil could bring your mixture back in, but if you do have plugs that are grossly different than the others there's another issue going on like with injectors or maybe even piston rings.

ChefYota4x4

iTrader: (5)

Another heheheh.... BTW; SUP ABECEDARIAN? lol...

Also, aren't the 95 still fired at the injectors off a Y-connector in the harness? IF NOT, nevermind... But if so, plugs one and 3 or 2 and 4, in pairs, showing rich or lean at the plugs could indicate an issue in that Y-connection of Power to 1 wire into 2 injectors(buddy had this problem, and it read lean, so the ECU signaled to dump more fuel... Not sure this would relate to your issue, either :>/ hehehe.)

Compression test is cheap and very telling, too.

Lankan

Will be going to visit a friend in Scottsdale, AZ tomorrow morning, so no time to fix/investigate much more. I will monitor the fuel consumption on the highway and get back to you guys with the numbers.

Off to check the voltage at the O2 and tripple check that I have no vacuum leaks!

ChefYota4x4

iTrader: (5)

Hey Lankan... I don't want to download your year FSM just to find it, lol... But I KNOW it's in there; Testing procedure for the "heated wire"/therein the "02" portion. It should also be in the troubleshooting section in "Emissions", next to the codes, right? Usually, in the tree-break down it shows "which section" you check for each code/troubled area where the 'tree' takes you to the left, "If NOT ok, test>>>" type stuff, ya know? You probably test at the ECU and 02, then can determine if it's a wiring issue or ground issue or whatever, ya know?

ChefYota4x4

iTrader: (5)

PS> OH YEAH, ... traveling mercies

SCToy

Well I failed smog today in CA with my 81. It wasn't even getting enough exhaust to the sniffer to do a test, plus the EGR apparently isn't getting vacuum. I fixed the exhaust, but still need to tackle the EGR before I can go back to retest

abecedarian

Not much up here. Had to sell my '89 Celica GT and '72 Firebird... got 700 for both. Guess that's better than homeless, no?

You mean "batch fired"? Yep, mostly. In mid-94 Toyota started implementing OBDII. Hence some rumors of 94 1/2 Tacomas (actually true, if you can prove it ) and that let them isolate issue to a particular cylinder. However, that was given to the 2R/3R/5VZ engines... and I think they do sequential injection instead of batch fired. I cannot verify that unless you send me those vehicles.

On the 22RE and 3VZE, all injectors fire once per engine revolution.

Even then, it's possible for either one of 2 or 4, or 1 or 3, to show rich. If one cylinder shows rich, it will make the other cylinders run lean.

At what point a cylinder (or two) runs rich causes the other cylinders to run lean... I don't know.

Compression test is cheap and very telling.

Sorry if I seem to be jumping around; dealing with lots of things here.

ChefYota4x4

iTrader: (5)

SC-TOY! WUTTUP, BRUDDA?????? Lonnnnnnnnng time no talkage! lol.

Sorry to hear, bud.... sux! I went through all of this on my CA smog failure thread, ... most of it's in my build, too. Not sure if you wanna read through all that, but I did post a lot about the EGR and Modulator in there. Testing procedures, etc. HOPE YOU GET IT SUSSED, ASAP! Seems REALLY common and SO MUCH more often in CA than anywhere else! Most aftermarket CAT's are CRAP, but magnaflow seems to be one of the better ones for aftermarket. However, yes, ...you gotta get the EGR stuff's sussed, first, before all else, lol.

abecedarian

barring other tests, if the ECU pops a 25- fuel mix lean.... the ECU has tried to adjust fuel mix and has no more room for adjustment.
Hence, the code being thrown.

SCToy

Hey chef! Yea, I haven't been working on the yota much lately, been doing a bunch of fabrication. I will definitely look over your thread if I can't get it figured out quick.

It does sound a whole lot better with my patched up muffler though.

ChefYota4x4

iTrader: (5)

Yeah, that's why I was hesitantly but curiously mentioning "MECHANICAL".... I HATE when that's the result for me, cuz it has meant, 4 of 5 times, TEARING THIS WHOLE FREAKING THING DOWN...... again, .... for as many times in HALF the years! LOL. ... But yeah, sounds as if something is wonky between either the Mechanical/EFI or IGN portions that the ECU just can't compensate for, .....hmmmm. Interesting and FRUSTRATING, I'm sure! lol.


I bet! No more "PUPPITYPUPPITY" OR "PFFFFRRRRRRRRRRT" SOUNDS! LOL.

Glad you're ok, man!

Maybe do some of the tests I did through the vacuum ports of the EGR to see if flow is actually getting TOO and FROM the EGR... I know the modulator is notorious for causing this.... If it doesn't gate the vacuum from the plenum right, I think it can cause the EGR to stick shut... But, if you're unable to cause a 'stall simulation' by applying vacuum via pump to the EGR inlet on top... then I'd say it's really clogged up somewhere in there or the EGR has failed(has too much of a hole or compromise in it to be closed(or is it open?) by vacuum pump. )

Lankan

Still checking stuff. Here's the link to tho online FSM.

http://www.ncttora.com/fsm/1990-1995...5/contents.htm

Can oone of you please help me find the "heater circuit" link and paste it on here?? I've been going through it and just cant seem to find it!!

rworegon

Is Page EG2-199 whatyou are looking for:
http://www.ncttora.com/fsm/1990-1995...e/troubles.pdf

http://www.ncttora.com/fsm/1990-1995...emci/eng3r.pdf

854x4

I just had a 95 toyota with a 3.0 come into the shop with code 25 and 26 after checking a few things we decide to do a compression test all was good except for cylinder number 3 it was 75psi and its in the valve train we havent tore it down yet. I think you might have misunderstood what I meant by a vacuum drop test when you apply vacuum to the egr valve engine should stall but it could be part restricted so you hook your vacuum gauge to manifold vacuum and then rev engine to 2500rpms and apply vacuum to the egr valve with the engine reved up watch your vacuum gauge and it should drop 6-8 in of vacuum if not it has a restriction. As for the heater wiring of the o2 sensor if its a 4wire then you have
heater+
heater ground
sensor signal
sensor ground
To test the heater circuit unplug o2 sensor hook multimeter to the heater + and ground wires and turn key on. You might have to start the vehicle but your meter should rear battery voltage. The heater wires for the o2 sensor are usually the same color so both will be either white or black.
As for exhaust leaks they only matter if its before the cat and if you do have one HC will be low and nox will be high because the cat uses oxygen to lower HC but it works the opposit for NOX. You might not have one because your reading shows 0. Hope this helps.

Lankan

rworegon, thanks a lot for the links! For the life of me I couldn't find these! Got a lot of reading and testing to do!!

854x4. Thanks for the clarification... I did misunderstand you the last time, so I'll do it the what you've mentioned reagarding the vacuum test. I'm hoping mine's not a compression issue! I checked the voltage coming to the O2 sensor with the ignition key switched on, and it was showing the battery voltage.