BT

I accidently posted this in the wrong forum, so I copied it here. I also forgot to list what truck I have. It's a 1991 Pickup, extended cab, 3.0 3vze, 4x4.

Ok, so like half of California, I failed smog. I failed at 15 miles per hour, passed at 25 miles per hour. HC's were at the borderline of failing, NO's double, making my truck a Gross Polluter.

I gave it a tune up (plugs, wires, cap, rotor) but didn't mess with the timing because the smog report says it at 10 degrees.

While replacing plugs, I found one of the emissions pipes , which connects to a vacuum solenoid, was not threaded into the header, it was loosely sitting in place. I fixed that and then noticed this threaded hole on a vacuum solenoid not connected to anything:


^Does anyone know what, if anything, should be here? ^

If you can see it in the photo, the nut connecting the rear pipe to the header is the part which was loose:


I also noticed this electrical connector without a plug nearby:


I don't know how to tell if my cat is bad, but this is what it looks like:


Also, there is only one O2 sensor. It is right in front of the cat. Should there be a 2nd sensor?

Lastly, I have Downey headers and a Downey cold air intake. Both are CARB approved.

Any input is appreciated.

Thanks.

Jay351

I have that same threaded hole with nothing there. Im pretty sure its normal.

Same with that electrical plug thats not plugged into anything. All the toyota trucks (in our generation at least) that I have looked at have it, and its not plugged into anything.

To check your cat you need to remove it. But since it appears to be welded, you are going to have to cut it out to check it.

Did you clean out your EGR valve? Check the EGR vacuum modulator. Mine is bad and caused my nox to slowly rise to a failure (over the years)

BT

I ran Seafoam through the brake lines twice, the gas twice, and the oil once. I'm pretty sure the Seafoam through the lines should have removed any carbon buildup.

As for the vacuum modulator, I'm not sure how to check it. I guess certain hoses should have suction at certain times, but I don't know the specifics. I have a repair manual I've looked through, but it isn't worth the paper it is printed on.

jason191918

There should only be 1 o2 sensor. Sounds like you already fixed the problem.

keithdphan

you have a non-california truck. so the egr does not have temp sensor. and only 1 o2 sensor.

Jay351

Look at the 93 FSM posted in the sticky in the forum. It shows you how to test the modulator.

seafoam won't clean out your EGR valve. You need to clean it by hand, the gunky crap is VERY hard to get rid of.

Make sure you don't have any vacuum leaks.

When was your o2 sensor replaced last?

BT

I've looked over the vacuum lines several times and haven't found any cracked hoses. I did the shadetree version of an EGR test (sucked on the hose and the truck stalled). Could it still be clogged enough to cause problems?

No idea on how old the O2 sensor is, at least a couple years probably. I priced one out at Kragen. They want $340. Will any 4-wire sensor work? I don't have any engine fault codes, so I don't want to spend that much if the sensor might be fine.

Also, could the PCV cause the failure? I tried to replace it but I couldn't free it from the valve cover. Seriously, could they have put it in a tier spot?

machabees

You can definitely get an O2 for less than that of you look around. I know that helped my truck alot. x2 on what jay said about that threaded hole very normal. PCV should also be replaced it's cheap insurance to know that it's good.
I don't know a whole lot about California emissions but there are certainly a couple good tricks to help get an engine to pass. One that I have used before is to run the tank down pretty low and then put in 4-5 bottles of dry-gas. the truck will run like crap but it should run. take it to the station have them test it ans it should pass with flying colors. then immediately take it to a station and fill it with gas otherwise that dry-gas will eat up your rubber lines.

BT

I'm thinking the loose pipe I tightened took care of the high NOx emissions, because now my truck gives a nasty, acrid smell. I'm guessing it is running rich now. Running rich is usually due to a bad O2 sensor, right?

jason191918

Can be. Check for CEL.

runethechamp

Just for your information, I had the fittings down to the header loose after my engine rebuild and I got a code 71 CEL out of it. Tightened it down and it went away. The CEL comes on if the temperatures aren't right, so I guess the air that was able to get in there or exhaust that could escape caused that to happen. Looking at my pictures I think that threaded hole is for the temp sensor, which is expensive by the way.

BT

So, my truck isn't a CA model, which the smog shop says doesn't matter as info is dug up by VIN.

But I failed again. I actually failed worse than before. So far I've changed the O2 sensor, Cat, plugs, wires, cap, rotor, PCV, all vacuum lines, and the EGR system passes a vacuum check.

Can oversize wheels cause a failure? I have 31/10.5R15 on but it was 225/75/15 stock, which is about 3" taller and 1.5" wider than stock, on 10" wide rims.

Could the wheel size have thrown off the gearing enough to cause a failure?

Also, the timing is at 7*BTDC (spec is 10)

BT

Ok, well even if no one has ideas of problems I'll keep updating to hopefully provide a reference to someone in the future with a similar problem.

I at least found a symptom: previously I only checked for proper function of the EGR valve, but not the circuit leading to it. It seems vacuum isn't making it to the valve.

Can anyone lead me on troubleshooting? The Chiltons manual I have isn't worth the paper it's printed on. I want to pull the filter out of the vacuum modulator to clean it, but I'm not sure if the top just pulls off. It's on tight and I don't want to break anything.

I also want to check the electrical switch controlling EGR vacuum. Does anyone know that procedure?

BT

Alright, vacuum is present at the top hose going into the green switch here, but it doesn't come out at the bottom. From here, it looks like it goes up to the EGR. Does anyone know how to check this? I think it is the VSV, is that right? Are they adjustable in some way? The black cylinder on the bottom can be rotated.

BT

So the VSV checks out, but that is as far as vacuum gets. Anyone have an idea?

SoCal4Running

I would remove and clean the EGR tubes, it is what cools your combustion chamber down to reduce Nox. The toyota egr system fully opens at too high of a rpm to be fully functional during the smog test.

If you havent re-geared for the 33's then a smaller tire would also help.

BT

Already pulled and cleaned the EGR (it didn't appear very dirty).

It seems to me that a signal is supposed to turn off to allow vacuum to pass through the VSV, but that it isn't happening.

Does anyone have a wiring diagram?

BT

Ok, so I bypassed the VSV because it it only is supposed to be closed when the truck is cold or at near full throttle.

And I failed smog again, but at least not due to NOx this time, although I only passed on NOx by about 50ppm. And I failed on HC's by about 25ppm.

I tested the PAIR system and found that VSV to not be opening either.

I want to bypass this also. The FSM says it is only supposed to be closed below 1000 rpm. Does anyone know if bad things will happen by allowing the PAIR to always work? The only thing I can think of is that I may have a miss at idle, although I just test drove with it bypassed and it seemed fine.

As for two VSV's being bad at the same time, I don't know... Perhaps the computer is not functioning properly, or the previous owner did something to disable the smog stuff?

js9924

dude you are missing your egr temp sensor they are about $109 without that the egr is not going to open. You should have a 71 CEL. If you want you can test the VSV's I think they are supposed to be around 40 ohms. If you want to get rid of the CEL and not replace the egr temp sensor just push a 10k resistor into the connector you said was just hanging there. but again the egr valve wont open without the sensor.

The pair just pulses outside air into your exhaust pipe to lower emissions. dont know what would happen as a side effect but I would say you need to be going to the junkyard with an ohm meter and getting some vsv's and an egr temp sensor.

Btw make sure all connections are clean and making good contact

BT

My truck isn't a CA model, it didn't come with an EGR temp sensor (nor a second O2 sensor). The EGR temp sensor doesn't control function, it just lets you know if it isn't functioning. I don't have a CEL nor any codes in the ECU.

Both VSV's ohm'd out fine, both ~37 ohms.

The previous owner put a cold air intake, Downey headers, and a stainless free flow exhaust on the truck. I'm thinking he may have also put in an aftermarket ECU that disables smog equipment.