Failed Smog due to high NOx at 15mph

[BeauJo]

I often come here looking for advise and I usually find what I'm looking for without ever posting. I'm not quite sure what to do with the information I'm finding so I wanted to ask some questions.

I had my 1996 4Runner SR5, V6, Manual, 280,000+ miles smoged here in Sacramento CA. It failed on Nitrous Monoxide at low speed 15 mph, and other measured values seem moderately high.

I know high NOx is from when the combustion is getting too hot.

The engine is old, but the people I bought it from had a huge binder full of maintenance records showing it was very well taken care of. Maybe there are carbon deposits in the cylinders? I have a can of Sea Foam... Would that help? I pulled out the spark plugs that were easy to get to to see what they looked like:

sorry the pictures are horrible. I think they look a little ashy? I have used Chevron injector cleaner fuel additive before, but only twice over the last 2 years. Anyway, I only looks at the 3 on the drivers side because they're easy to get to.

I want to say part of the problem may be the catalytic converter because of the other chemical values.

Here are the ASM Emission Test Results:
15 MPH
RPM: 1483
%CO2: 15.1
%O2: 0.1

HC(PPM)
MAX: 50
AVE: 7
MEAS: 39

CO(%)
MAX: 0.64
AVE: 0.03
MEAS: 0.12

NO(PPM)
MAX: 508
AVE: 90
MEAS: 907

25 MPH
RPM: 1687
%CO2: 15.0
%O2: 0.0

HC(PPM)
MAX: 34
AVE: 6
MEAS: 20

CO(%)
MAX: 0.78
AVE: 0.03
MEAS: 0.08

NO(PPM)
MAX: 761
AVE: 84
MEAS: 665


There are no codes reported.

I took a propane torch and ran gas all along the vacuum lines according to the diagram under the hood. There was no change in idle.

I have an extremely limited budget to get this working. CA has a repair assistance program that I should be able to get some help from. I just want to get an idea of what could be wrong before I have to work with a shop that's sponsored by the state's program. What do you think?

 

[BlackCat914]

The plug does look a bit white/lean. I'd throw some 105+ octane in the tank, drive it a bit, and then re-smog it. Race fuel burns cooler and slower, drastically reducing NOx output.

 

[fish0281]

It's hard to tell from the picture and I doubt it would contribute (definitely won't help) to your emissions issues, but that plug looks pretty worn. The seafoam won't hurt, BG-44K is another similar product to try...

Otherwise, at that mileage and (I assume) the original cat, it shouldn't surprise you to have higher emissions levels - things only work as designed for so long!

 

[bikerjosh]

Had the same issues, turned out it was the cat. After changing a cr%p load of stuff the smog tech diagnosed the cat. Bought a cheap CARB certified cat and it passed.

Also heard you can throw a mixture of denatured alcohol into the tank to clean up the numbers.
Josh

 

[JohnsD90]

I would take it out on the highway and really give it a good run, floor in in 2-3-4-5th and really just burn the extra crap out of the CAT, it should smell a little, sometimes it good to really put cars through there paces every once in a while. Then I would put that additive in that helps lowers emissions to help you pass, I really wouldn't worry about the nox emmisions being to high, as long as it passes just leave it as is.

 

[mikebontoft]

Oxides of Nitrogen (NOx) are formed at a temperature above. . ah I can't remember anymore. I think it's 3200*. Anyway, as you know... high combustion temps.

it appears both from your plug and what I believe is a little lower Hydrocarbon reading than a 4runner should have, that you're running lean. (39ppm is close to new economy car territory.)

When was the last time the fuel filter and the front oxygen sensor (s) were replaced?

Aside from that, it could very well be the cat getting more air than it should (from a lean engine!), crossing over that threshold and creating NOx. That would explain the lean looking plugs as well.

 

[stevec5000]

Like they said NOx is caused by high combustion temperatures. It is reduced by the EGR system which recirculates exhaust back into the combustion chambers to dilute the fuel mixture so it won't burn as hot. If you vehicle failed then your EGR wasn't working or wasn't working to it's full capacity. You can test it by using a hand operated vacuum pump connected to the EGR valve. When you apply vacuum it will kill the engine at idle when it kicks in! You could have carbon plugging up the passages inside the head but I suspect a cracked vacuum line or sticky valve is more likely.

 

[Buckaroo]

Agree with stevec.....something is restricting you exhaust gas recycling system. As he said, if you manually pull a vacuum on the EGR valve, it should open. At idle, the introduction of exhaust gas will cause the engine to stumble and likely die. If that happens, your valve and the pathway through the head are likely OK...look for a leak in the vacuum system. If the engine does not die, look at replacing the EGR valve. Also look for carbon deposits in the pathways through the head. You may need to carefully ream them - you can use thin, metal springy steel (like the spine from an old windshield washer). Careful not to drop anything down the holes.

Good luck and keep us posted.

 

[kball]

3rd gen 4runners with the V6 don't have EGR's.

 

[bikerjosh]

3rd gen 4runners with the V6 don't have EGR's.

Oh yeah, there is that.

 

[mikebontoft]

That is true JDM then... I believe most domestic (IN Japan) Japanese engines do not have EGRs. Surprised this one doesn't though.

 

[BeauJo]

Yeah, no EGR valve on this one. I looked back through the records I have from the previous owners and this is what I found:

Fuel filter replaced 9/2009 244581 miles Probably a good time to replace this again
Side note, they also replaced the spark plugs at this time. I cleaned up the three easily accessible plugs, and I'll get to the other side this weekend.

Thermostat replaced 4/2007 211217 miles (the rubber seal has detached from the radiator cap, but it's still there. I think it still works alright.) Am I mistaken to think that the coolant system would not significantly effect the combustion temperatures?

O2 sensor replaced 5/2003 133930 miles (part number 89465-39895 looks like the up-stream) Would the O2 sensor be an issue even if it's not generating a code?

No record of the cat converter ever being replaced.

I filled up with Chevron 91 octane yesterday. I usually run mid grade 89.

Also I'm wondering if tire pressure might have an effect. I imagine if the tires have more less pressure they would create more resistance and put more of a load on the engine. My thinking is this would require more throttle which would create a richer mixture. Not sure if that last assumption is correct. Something lowers the NOx at higher speed/RPM. Maybe the cat is just getting hotter.

 

[fish0281]

Yeah, no EGR valve on this one. I looked back through the records I have from the previous owners and this is what I found:

Fuel filter replaced 9/2009 244581 miles Probably a good time to replace this again
Side note, they also replaced the spark plugs at this time. I cleaned up the three easily accessible plugs, and I'll get to the other side this weekend.

Thermostat replaced 4/2007 211217 miles (the rubber seal has detached from the radiator cap, but it's still there. I think it still works alright.) Am I mistaken to think that the coolant system would not significantly effect the combustion temperatures?

O2 sensor replaced 5/2003 133930 miles (part number 89465-39895 looks like the up-stream) Would the O2 sensor be an issue even if it's not generating a code?

No record of the cat converter ever being replaced.

I filled up with Chevron 91 octane yesterday. I usually run mid grade 89.

Also I'm wondering if tire pressure might have an effect. I imagine if the tires have more less pressure they would create more resistance and put more of a load on the engine. My thinking is this would require more throttle which would create a richer mixture. Not sure if that last assumption is correct. Something lowers the NOx at higher speed/RPM. Maybe the cat is just getting hotter.

Why not replace the plugs while you've got them out?

You will not change anything with higher octane unless you have reason to believe the low octane (87) is dirty.

I don't believe your O2 sensor would cause an issue without throwing a code. Just to be clear, the downstream (relative to the CC) sensor is the O2 sensor and only detects emissions. The sensor upstream is actually an Air-Fuel sensor and is what the engine uses to maintain a stoichiometric condition (proper balance between fuel and air for complete combustion).

I really doubt tire pressure would lead to these issues - lower pressure (like 10psi or lower) would cause a heavier load and thus a more rich condition, but at cruise speed (not accelerating), the engine is trying to maintain a stoichiometric condition.

I am willing to bet that it's only a matter of time before your engine throws a P0420 code. The cat has a finite life and durability, it's probably hanging on by a thread right now and the emission sniffer machine is more sensitive (and detects a wider range of emissions) than the O2 sensor... Just for $hits and giggles, have you made sure your air filter is seated correctly, intake is not loose, and your throttle body is positioning correctly?

 

[chadsy]

O2 sensors can get lazy without throwing a code.

I've read to replace them every 100K miles.

 

[BeauJo]

Update: Replaced Fuel Injector and Fuel Filter

I have a big update but I want to make some replies first

Why not replace the plugs while you've got them out?

You will not change anything with higher octane unless you have reason to believe the low octane (87) is dirty.

I don't believe your O2 sensor would cause an issue without throwing a code. Just to be clear, the downstream (relative to the CC) sensor is the O2 sensor and only detects emissions. The sensor upstream is actually an Air-Fuel sensor and is what the engine uses to maintain a stoichiometric condition (proper balance between fuel and air for complete combustion).

I really doubt tire pressure would lead to these issues - lower pressure (like 10psi or lower) would cause a heavier load and thus a more rich condition, but at cruise speed (not accelerating), the engine is trying to maintain a stoichiometric condition.

I am willing to bet that it's only a matter of time before your engine throws a P0420 code. The cat has a finite life and durability, it's probably hanging on by a thread right now and the emission sniffer machine is more sensitive (and detects a wider range of emissions) than the O2 sensor... Just for $hits and giggles, have you made sure your air filter is seated correctly, intake is not loose, and your throttle body is positioning correctly?

Thanks Fish for the detailed reply. I do need to change the spark plugs. I'm just trying to fit it into my budget.

After all of the varying comments on grades of gasoline, I did some searching and found from some reliable sources that you're right about octane. Higher octane only makes a difference on vehicles designed to use it. As far as a lower grade being dirty, at least here in CA the quality of gas is tightly regulated among all grades of gas.

As far as the O2 sensor. From what I've found online and on the forums one of the main causes of high combustion temperatures causing high NOx is a lean air/fuel mixture. So changing the upstream O2 sensor would hopefully help even it out a little more. It has been 150,000 miles since it was replaced.

The cat is no doubt lacking. The air filter is good, and seated correctly. I'm not sure what you mean by if the throttle body is positioning correctly. As far as the intake I've just re-installed it. This leads right into the latest news.

So I decided to do a sea foam treatment to try to clean up carbon deposits in the cylinders which I've read increase temperatures. I really baby the gas pedal normally so I decided to rev it up to 3500 4000 rpms a few times while it was burning off the sea foam out of the cylinders. (Side note: I don't know if I should have done it but I did two treatments... The second time after putting the sea foam in the pcv vacuum line, when I shut off the engine it dieseled for around 5-10 seconds.) I thought everything went pretty well, until later that day when I was driving some surface streets, it started running really rough and the check engine light came on. The code said cylinder 4 misfire. Did some research and found some info on WhichHunter that brought me to the conclusion it was the injector because I've also heard faint pinging noises when the engine's cold under moderate acceleration. When I got at the injector it was reading around 140 ohms where all of the others were reading 15.5-15.2 ohms. Replaced it along with o-rings on all the other injectors using these guides and other info I found here and there:
Autozone Repair Guide: Fuel Injection
Autozone Repair Guide: Intake Manifold

I also replaced the fuel filter.

There was a noticeable performance increase, and my time for a free retest was up that day so I went to take it in. It was pretty close to passing:
NOx
Max: 508
Meas: 550

All other emissions were below average now which was awesome. The guy at the test station said that if it's been running dirty on most of the emissions for a while it's probably burned up the catalytic converter.

So to me some of the probable suspects are most likely the upstream O2 sensor, and now that I'm thinking about it the remaining fuel injectors probably really need cleaning. These two things might help get a richer air/fuel mixture which I understand cools things down reducing NOx. And of course the cat... I guess I'm going to be living on beans and rice for a while, and I'll shut the power off (good thing it's starting to get warm out). Got to get this thing fixed!

 

[k2damfc]

Also what I’ve done in the past is get tank to about 1/4 tank then put $20 of e-85 in. Some tech at Toyota taught me that trick. Brought my emissions down a lot but in the end I ended up having to replace my O2 sensor anyways. Now I usually always consider that option

 

[BeauJo]

Solved

Hate it when the OP never post if they ever figured out what was wrong and how it was fixed.

Anyway I replaced the catalytic converter, cat, and the emissions were better than the best reference values given on the report!

Thanks everyone!

 

[MountainBiker]

Hate it when the OP never post if they ever figured out what was wrong and how it was fixed.

Anyway I replaced the catalytic converter, cat, and the emissions were better than the best reference values given on the report!

Thanks everyone!

Glad you got it fixed, and thanks for posting what it took to fix it!