Emissions fail: high NOx getting higher? (2 Viewers)

[imhighlander]

My new-to-me JDM hundo isn't clearing emissions. When I first tested at emissions, I got the following values:

• HC GPM 0.0903 (state limit is 0.8000)
• CO GPM 5.7097 (state limit is 15.0000)
• CO2 GPM 646.6110
• NOx GPM 3.443 (state limit is 1.5000) This is what failed me.

The vehicle was running a bit rough and has very low miles (73k) for a 1998 model, so I had assumed bad plugs and bad fuel/clogged injectors. I ordered and installed new plugs (NGK Iridium) and have cycled a bunch of injector cleaner through the vehicle over the course of about 8 weeks. When I changed the plugs I also checked the coil packs and all of them appeared to be in perfect condition. I've probably put 10 full tanks of 91 octane gas (plus various additives like Seafoam, LiquiMoly, etc.) through the vehicle since I installed the plugs. The vehicle has run a fair bit better, but I still don't think it feels "right."

I took it to a local "Toyota specialist," who seems to be generally useless. They hooked it up to "their computer" and found no misfires and couldn't otherwise find a problem with the rig. They told me that the high NOx was likely due to bad gas and that my efforts in running higher octane fuel, my spark plug switch, and various OTC fuel injector cleaner concentrates through the system would solve the problem.

Last week I went back to our emissions testing center and got the following results:

• HC GPM 0.1687 (higher than before)
• CO GPM 5.6311 (roughly the same, slightly lower than before)
• CO2 GPM 612.2163 (a bit lower than before)
• NOx GPM 5.6147 (actually HIGHER (e.g., WORSE) than before)

So I failed again, and my NOx is moving in the wrong direction. I'm looking for a more competent Toyota diagnostician/mechanic in the Denver metro but as I continue my learning, what should I be checking for next? I have not had any CELs at all.

I have replaced the plugs, I have checked and verified (visually) the condition of the coil packs, I've been running at least 10 tanks of high octane gas, and I've run half a dozen applications of R22, LiquiMoly, or Seafoam through the gas to try and clean the injectors. Is there anything other than a catalytic converter I should be thinking about?

I can't imagine that a 73k mile rig might neet a new catalyst, but I don't know enough about the emissions system to think about what else might be causing high NOx.

Any help is greatly appreciated.

 

[J1000]

Low HC shows that you are getting good combustion so the engine is likely running fine.

I would recommend cleaning the MAF if you haven't yet.

Most likely the catalytic converters are bad. Low miles means the truck has been sitting for most of its life. Sitting is bad for cats. Low miles also indicative of driving short distances without allowing the truck to fully warm up, also bad for cats. In Japan it could have also been sitting somewhere humid so failed cats are not out of the question.

 

[Wadepat2]

Just a guess from me but I would run regular octane fuel and stop the additives. Clean maf.
Let it run a full tank without all the additives . Take a with a few hour long highway drives. OD off to keep rpms up to burn off anything in cats. A few hard pulls through the gears. Retest.

 

[imhighlander]

Thanks for these replies. This weekend I'll clean the MAF and replace the air filter; hadn't checked those yet. I'm also thinking EGR based on the wave values from the emissions report. I've included that image below.

From a video I watched last evening, the high NOx readings under acceleration at at "cruising speed" may indicate that the EGR is not opening. For you guys with more experience than me, does this data suggest anything further to you?

(Also note crazy low VIN!)

 

[J1000]

Worth cleaning the EGR, definitely.

 

[kerrye]

The EGR is designed to lower NOX readings. A bad vacuum modulator or EGR valve can cause high NOX. Urban Car Care on East Evans has gotten my NOX readings down low enough on our 80 series to pass the test. I've found no direct connection between octane levels or ethanol/non-ethanol fuels and lower NOX. When I looked at my graphs it looked to me as though NOX was highest just after upshifting. So, I've turned off overdrive and set the transmission on 'Power'. to raise the rpm's when shifting and theoretically lower NOX on the upshift. I'm also of the opinion that how the vehicle is driven on the dyne can have an effect on emission levels. I've taken two tests within 20 miniutes of each other (gas cap was bad) and the results were way different even though nothing had been done to the vehicle in the meantime.

 

[imhighlander]

Following up with what feels like a dumb question, but Google searches and review of the FSM and I don't see the EGR referenced for the 100 series. Surely there IS one, and I suspect I can find it lurking near the throttle body. But if anyone has a step-by-step on the 100 series EGR, I'd be grateful for the link. All the links I'm finding reference the 80 series, even when I add "100 series", "1998," and "2UZ-FE" in my search string.

 

[saucebox]

LC100 Workshop Manual - https://lc100e.github.io, then Engine Repair Manual, then Emission Control System to see everything connected.

It starts like this, then goes through each of the systems

 

[J1000]

Following up with what feels like a dumb question, but Google searches and review of the FSM and I don't see the EGR referenced for the 100 series. Surely there IS one, and I suspect I can find it lurking near the throttle body. But if anyone has a step-by-step on the 100 series EGR, I'd be grateful for the link. All the links I'm finding reference the 80 series, even when I add "100 series", "1998," and "2UZ-FE" in my search string.

I was gonna say, I don't think there is an EGR. At least I know there is not EGR on the VVTI engine but unsure on the earlier engines.

 

[imhighlander]

LC100 Workshop Manual - https://lc100e.github.io, then Engine Repair Manual, then Emission Control System to see everything connected.

It starts like this, then goes through each of the systems
View attachment 3581437

Thanks much!!

 

[imhighlander]

I was gonna say, I don't think there is an EGR. At least I know there is not EGR on the VVTI engine but unsure on the earlier engines.

This would explain my lack of any hits. Thanks

 

[imhighlander]

Back to this thread and still chasing high NOx. I pulled the OEM cats and they were clearly perished. They rattled like a set of large maracas full of gravel. I replaced them with new Magnaflow CARB-compliant cats and did notice a little improvement in acceleration up hills. But when I took it for emissions testing, I again failed for high NOx. By now, i have done the following:

• New spark plugs (NGK Iridium)
• Cleaned throttle body
• Cleaned MAF
• Replaced air filter
• Replaced catalytsts
• Run several full tanks of high octane fuel with a variety of in-tank engine cleaners (Seafoam, 44k, etc.)

I believe I'm at the end of my DIY rope and haven't yet found a good shop in the Colorado Front Range/Denver area who seem to be able to diagnose my problem. The vehicle still doesn't feel like it accelerates as smoothly or evenly as it should, almost like a misfire while accelerating under load (e.g., uphill pulls). It's subtle, but I definitely notice it.

I have shown no CEL and one shop that claims to specialize in Toyotas said they found no error codes with their computers. Here are my emissions readings in chronological order, all from the same emissions control facility in Littleton, CO:

Test 1:

• HC GPM 0.0903 (state limit is 0.8000)
• CO GPM 5.7097 (state limit is 15.0000)
• CO2 GPM 646.6110
• NOx GPM 3.443 (state limit is 1.5000) This is what failed me.

Test 2, after spark plugs and a few tanks of high octane fuel & cleaners:

• HC GPM 0.1687 (higher than before)
• CO GPM 5.6311 (roughly the same, slightly lower than before)
• CO2 GPM 612.2163 (a bit lower than before)
• NOx GPM 5.6147 (actually HIGHER (e.g., WORSE) than before)

Test 3, after cleaning the throttle body, the MAF, replacing the air filter, and replacing the failed OEM cats:

• HC GPM 0.2717 (higher than both prior values)
• CO GPM 2.4435 (less than half of test 2 value)
• CO2 GPM 649.3360 (slightly higher than both prior values)
• NOx GPM 4.6953 (higher than test 1 value, slightly lower than test 2 value. Still much higher than max limit of 1.5000)

I could certainly replace the MAF and the O2 sensors, but I'm chasing a mystery. Is there anything else I'm missing? If anyone has an excellent emissions service specialist in Denver area, I'd be grateful for the referral. Some folks have told me they work on such an old vehicle (ridiculous! It's a 1998!) or they want to keep it for 4-5 hours of diagnostic work at around $120 per hour.

Grateful for any guidance.

 

[kerrye]

Urban Auto Car on East Evans has resolved emissions problems on my 80 series a few times. Can't directly speak to their expertise on 100 Series. I think they charge around $200 minimum diagnostic fee.

 

[J1000]

Have you been pulling the battery terminal for 30 seconds or so in between all the changes to reset the ECU? Definitely reset the ECU and put some miles on it in between tests. I would reiterate what @Wadepat2 said and stop using fuel additives and run the truck on mid-grade 87 octane instead of premium.

The vehicle still doesn't feel like it accelerates as smoothly or evenly as it should, almost like a misfire while accelerating under load (e.g., uphill pulls). It's subtle, but I definitely notice it.

To me, this sounds like the fuel pump is weak. These trucks have multiple speed fuel pumps so light acceleration up a hill uses the low speed, then changes to full speed when you floor it. So if it feels good at wide-open-throttle but stumbles during partial throttle that points to fuel pump. Lean combustion will result in high NOx. When it does this it will not throw a CEL either.

 

[Wadepat2]

Have you been pulling the battery terminal for 30 seconds or so in between all the changes to reset the ECU? Definitely reset the ECU and put some miles on it in between tests. I would reiterate what @Wadepat2 said and stop using fuel additives and run the truck on mid-grade 87 octane instead of premium.


To me, this sounds like the fuel pump is weak. These trucks have multiple speed fuel pumps so light acceleration up a hill uses the low speed, then changes to full speed when you floor it. So if it feels good at wide-open-throttle but stumbles during partial throttle that points to fuel pump. Lean combustion will result in high NOx. When it does this it will not throw a CEL either.

Maybe a little lean also? Wouldn't hurt to check vacuum pressure and for any small leaks? Lean will have it run hot, feel sluggish at part throttle and I believe causes high nox. Just a guess really. Always good to double check all the old vac lines with the maintenance already done.