Emissions issue 99 4 Runner

AustinSN

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My buddy's 4 runner keeps getting failed for high NOx. 3.4 v6, slushbox, 4x4, non-cali truck, 260k miles or so.

These don't have EGR, we looked on various forums and most people suggest a new front O2 and a MAF cleaning, we did both of those on Saturday and while the NOx lowered, it's still failing.

Any other suggestions? We spent a good 20 minutes going through the vacuum lines, one was suspect on the end but we added a clamp to it and feel it's not an issue.

Next move is to put seafoam in the tank, and do a proper seafoam procedure. He already tried throwing a bunch of HEET in the tank and getting it retested but failed that too lol.
 

2011 gtcs

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Is it setting a DCT or are they sniffing the tailpipe? They usually dont do that with OBD2 cars. Either way if you're getting high NOX I would probably start with replacing the front 02 sensors as well, cleaning the MAF and if anything mix some E85 into the tank, high NOX comes from high combustion temperatures, mix maybe 1 gallon in when you fill up.
 

AustinSN

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Is it setting a DCT or are they sniffing the tailpipe? They usually dont do that with OBD2 cars. Either way if you're getting high NOX I would probably start with replacing the front 02 sensors as well, cleaning the MAF and if anything mix some E85 into the tank, high NOX comes from high combustion temperatures, mix maybe 1 gallon in when you fill up.
Sniffer.

It's not pulling a light and the light functions.

They have 2 O2s, the first one is actually used, the after cat is to throw a CEL if it fails. I guess the logic was if they are both the same, they should both die at the same time.

We replaced the before-cat O2, no exhaust leaks either.
 

gt347mustang

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How high is HC and CO? If those are near the limit too then the cat is done. If they're super low its burning lean and could likely pass if you're able to richen it up.
 

wundrbird

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Since high NOx production is caused by high cylinder temps, try tuning up the cooling system.

Flush the cooling system to get rid of buildup, and make sure there are no clogs. Buildup can create hot spots around the cylinders.

Fill with the proper mix of distilled water and antifreeze. Too high a water concentration might allow for boiling and create hot spots. Too high a coolant concentration can cause a blanket effect and not take heat away from the cylinders.

Replace the coolant temp sensor. If it's weak or bad, it's sending poor or no signals to the computer.

Get a new thermostat, maybe one that opens at a lower temp. An old, worn thermostat might allow the engine to get too hot before opening.
 

AustinSN

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Original catalytic converter?

We think so. I banged on it from under the vehicle to see if it had broken loose inside, it could be partially clogged.

Check the catalytic converter temps hot if you have a temperature scope.

I don't have a temp scope, and my temp gun only goes to 640.

Is shooting them from the outside a reliable diag method? What should they be?

How high is HC and CO? If those are near the limit too then the cat is done. If they're super low its burning lean and could likely pass if you're able to richen it up.

Both within range but I don't know if it's actually high for these things. Looking at the paper:

HC: tested .6216 limit 1.2
CO: tested 11.1553 limit 15.0

Of course there are no units, so whatever the **** that means.

Since high NOx production is caused by high cylinder temps, try tuning up the cooling system.

Flush the cooling system to get rid of buildup, and make sure there are no clogs. Buildup can create hot spots around the cylinders.

Fill with the proper mix of distilled water and antifreeze. Too high a water concentration might allow for boiling and create hot spots. Too high a coolant concentration can cause a blanket effect and not take heat away from the cylinders.

Replace the coolant temp sensor. If it's weak or bad, it's sending poor or no signals to the computer.

Get a new thermostat, maybe one that opens at a lower temp. An old, worn thermostat might allow the engine to get too hot before opening.

The radiator is brand new, the old one had a small weep. I don't think it runs hot. No idea on the T-stat. I guess if we put in a colder one the car should try to richen the mixture which could drop the NOx...


Curious if it is the cat. I told him to Seafoam it, outside the city lol.
 

svtfocus2cobra

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I don't have a temp scope, and my temp gun only goes to 640.

Is shooting them from the outside a reliable diag method? What should they be?

640° should be high enough. You check the temperature on the pipe just pre-cat and then the temperature after cat and there should be at least 100° difference. At normal operating temp just idling you shouldn't see temps any higher than 400° really.
 

AustinSN

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640° should be high enough. You check the temperature on the pipe just pre-cat and then the temperature after cat and there should be at least 100° difference. At normal operating temp just idling you shouldn't see temps any higher than 400° really.
Awesome. Thank you.
 

Crimson2v

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Check your scanner, if the rear O2s are switching then the cat is done. It should also throw cat efficiency codes if they are failing. What are your st and lt trims?
 

kevinatfms

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We think so. I banged on it from under the vehicle to see if it had broken loose inside, it could be partially clogged.

Both within range but I don't know if it's actually high for these things. Looking at the paper:
HC: tested .6216 limit 1.2
CO: tested 11.1553 limit 15.0

Of course there are no units, so whatever the **** that means.

Curious if it is the cat. I told him to Seafoam it, outside the city lol.

Replace the converter.

And Hydrocarbons/Carbon Monoxide are measured in PPM.
 

kevinatfms

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I told him.

Since the NOx is rather close, we are going to try Seafoam first then it's going to get a cat if that doesn't work.

The issue with using Seafoam at this point is that everything its going to "steam clean" as it works through the engine is going to end up in the converter anyways.
 

nxhappy

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if hes gonna keep the turd for a while , might as well do the cats.
 

AustinSN

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if hes gonna keep the turd for a while , might as well do the cats.
That's the thing, he bought this as a temporary car for cheap(2 years), after his WRX was stolen.

But if it won't pass, it won't pass.
 

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