reallifedog

Hey guys, I've been having a hell of a time trying to pass emissions and I'm really close just a little high on my CO numbers. My mechanic tested my current o2 sensor and it's not oscillating, put a new one in and same deal. Confirmed it had continuity so I don't think it's wiring. He retarded the timing for my second emissions test in hope that'd bring down CO levels and it made it worse. I'm not very well versed in combustion emissions but from what I've read I was able to go about 4 clicks lean on the vafm and adjust idle screw to smooth it out to 850 rpm warm(previous owner noted it'd die once warm and it seemed and smelled like it was running rich, now no longer an issue). PO also said the engine was rebuilt but has no records so may be a junkyard motor, regardless of was kinda a hack job. I'm considering replacing the ECM but not trying to waste unnecessary money. I hope this is sufficient info to at least get wheels turning but I will check whatever else or take pics of you guys can offer some insight.

Thanks guys.

RJR

If the O2 sensor isn't oscillating, your engine isn't running closed loop and consequently the mixture is wrong for the cat converter, most likely too rich since you're failing CO.

Get a voltmeter and measure the VF1 terminal on the diag connector while the engine is warmed up and idling. Also measure it while running at 2500 rpm, again, with it warmed up. The voltage should be between 1.25 and 3.75 volts. If it's stuck at or near 0, you're running rich and the ECU does not have enough range to correct it. If it's stuck near 5 volts, the ECU is getting bad data from one or more sensors and is trying to enrich the mixture even though it's already too rich.

Next jumper the TE1 to E1 and do the same tests on VF1. This will tell you what the ECU thinks the O2 sensor is doing. Since the engine is running rich, you would expect the VF1 terminal to be at or near 5 volts. If it's stuck at 0 instead, the O2 sensor is lying to the ECU, which is why you're running rich.

If you can make those measurements and report back, maybe we can give you a bit more guidance. Also check out the articles in the OBD1 section of this website.
http://www.autoshop101.com/techartic...cles.html#OBD1. Look especially at articles 24 through 27.

Oh, and BTW, mucking with timing to fix emissions is not the right approach. If the cat converter is working and the system is running in closed loop, the engine will easily pass emissions. If it doesn't pass, it's because something is wrong in the ECU/O2 sensor control loop, or your cat converter is shot.

RBX

Make sure it isn't a Bosch O2 sensor. They are know to cause issues.

Punchy

^^^^ What he said


Check that the EGR is not stuck open and that it is connected to the correct VSV (Green) correctly, The EGR modulator new?

reallifedog

Sounds like I will definitely need to bust out the multimeter when I get home. when checking the VF1 am I going to another port, grounding to frame or something else? and you're definitely right about screwing with the timing but I figured this guy might know something I didn't...

Is there branding/serial on a bosch sensor?

EGR definitely appears to be original, not sure if its stuck but I will find out how to check that.


Thanks for the direction guys, looks like I have some more stuff to research. Its crazy just coming from the forum and talking to the mechanic I feel like he either doesn't know toyotas(maybe this engine?) very well or is withholding information. Either way thanks for not making me sound like a complete noob in discussion

RBX

Download the FSM (field service manual).
Keep in mind most mechanics aren't on forums talking about brand specific or known issues. He is giving you information based on his knowledge with a variety of vehicles. But with the availability of the web, he should do some homework.

scope103

What RJR says. Here's a specific page at autoshop that will move you along in your understanding of emissions http://www.autoshop101.com/forms/h56.pdf Note that your elevated CO is almost certainly caused just by running rich. And as RJR says, your O2 sensor is not oscillating because no matter what your ecm tries, it can't lean out the mixture far enough (while you COULD have a bad O2 sensor, it's giving you the same answer as the smog-guy's fancy 5-gas analyzer, so I wouldn't bother with that yet.)

It's probably not the EGR; that would slightly lean the mixture if it were stuck open. As well as making it run badly.

The first thing I would do is to undo whatever "adjustment" was made to the VAF. As RJR says, these trucks will pass smog every time if they are working half-way properly. And since you are never supposed to mess with the VAF, your adjustment is just moving away from the point where it will eventually work.

reallifedog

Thanks Scope, that makes sense- too many bandaids, I need to start fixing stuff.


I really appreciate all the info guys, faith is slowly but surely being restored in me that this thing is going to pass.

EDIT: Im not sure if this is at all helpful but here's the emissions tests numbers right now:

#1


#2

Punchy

Negative!
The EGR is letting in inert atmosphere which lacks O2 and makes the fuel burn cooler (More HC and less NOX), When stuck open it boggs the engine and produces a lot of unburnt fuel and that cycles back around redundantly making it worst.

RJR

Check VF1 against the E1 terminal of the diag port. However, E1 is just the ECU's version of ground, so for this measurement grounding your meter to the frame or the negative terminal of the battery is just fine.

Punchy

By your test and you mentioning the last owner rebuilt, If it was a HG problem then the O2 sensor and CAT are contaminated by coolent.
Since all your readings are really high and improve through a RPM increase which sends more heat to the CAT, Bad CAT.

RJR

There could be a bad cat involved, but that wouldn't keep the O2 sensor from oscillating, since it's upstream of the cat. Something is still wrong in the air/fuel control loop that needs to be fixed, or even a brand new cat converter won't get the job done.

reallifedog

Also, just ordered a replacement ECU(88-92) from ebay so Im gonna throw that variable into the mix this weekend. I'd sure be glad if that was the culprit but we will see...

reallifedog

Alright so @RJR I tested how you suggested and it consistently read 0.04v without budging once except for a second down to 0.02v during idle. I'm still reading up but any hints would sure make my day.

RJR

OK, I'm assuming that measurement you just did was the VF1 pin without TE1 connected to E1. That tells us the ECU thinks the mixture is too rich and is trying to lean it out, but has run out of range to do so.

Make that same measurement with TE1 connected to E1. That'll tell us what the O2 sensor is doing. When working properly, it should be oscillating about once/second, but in your case will likely be stuck at 5 volts, indicating that the O2 sensor also thinks the mixture is too rich. If that is the case, the O2 sensor is giving good data, and something else is causing a rich mixture. As has been said, it could be the EGR valve stuck open.

You could try plugging the EGR to see if the O2 sensor starts working properly. If so, you'll have found your problem. Meanwhile, we'll try to think of other areas to look at.

reallifedog

It was reading 0.04 with and without the jumper. Now to figure out how to plug the egr...


EDIT: OK not sure how i missed this but....



i cant seem to find any loose connectors but I can dig more.

RJR

I may have misled you a bit in my first post. If the throttle is completely closed so that the idle switch is closed on the TPS, you'll get 0V for both of those measurements. The throttle has to be slightly open so the TPS switch is open. That's why I suggested also doing the measurement at 2500 rpm, where you're sure to get valid readings on VF1.

If you truly are getting 0V both with and without TE1 shorted, and the throttle off idle, you have a confused control loop. The O2 sensor is telling the ECU to enrich the mixture, and the ECU is doing its best to lean it out, and it's still too rich. You might want to check continuity from the O2 sensor and the diag port back to the ECU.

reallifedog

If I do need to re-run wire to O2 sensor from ECU, how sophisticated does it need to be? can I just cut and solder into the harness or will I need to replace the entire harness?

thanks

scope103

Re-check continuity, however you did it, before you start replacing wiring. As far as how "special" the wiring is, the OX1 lead (Black) is inside shielded wire (according to my wiring diagrams).

I assume you have a heated (4-wire) O2 sensor. You should get a code if the wiring to the heater (R-G, B-R) opens, but I guess you could have just opened the sensor wire. If your voltage measurements are approximately correct, an open sensor wire would make sense.

oldblue

an air flow meter that hasn't been tampered with would be nice to try. maybe a cold start injector thats dripping a little. an egr that is not fully closing could cause it. i doubt its a bad cat, usually nox is high with that. check your air filter and make sure it isn't clogged. emissions are a pain for sure.