Failed smog test...Any cheap quick fix ideas?

Dbiz

Dbiz

New member
So I took the truck in for a smog test today and it managed to barely not pass. Everything was better the average except my NO (PPM) measurements were just a bit high at 15 MPH. It passed at the 25 MPH mark but was way above the average. The max for the 15 MPH was stated to be 508 and my measurement came in at 566. So now my options are to either take it to a mechanic and have him run a diagnostic and figure out what is wrong or to try and fix little cheaper things in hope that it'll solve the problem.

So my main question is what could possibly be failing and are there any cheap options to fixing these things myself instead of paying a couple hundred to have a mechanic do it.

I know it could be the catalytic converter, or possibly the oxygen sensors. However, not exactly sure how to check those out myself.

Any help would be much appreciated.

Thanks in advance!
 
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Is it a tailpipe test? If so then disconnect the pipe from the muffler, and only let some of the exhaust through.

If not then just clean the MAF sensor, throttle body, and change the plugs and oil.
 
The plugs and wires shouldn't be the issue. Replaced them only a few months ago. I am about due for an oil change...Could also look into cleaning the MAF. It was the tailpipe test at 15 MPH that was failed.
 
maybe dump some Lucas fuel treatment in the gas tank next time you fill up?? im not sure if it's legit but i do it every 4 to 6 months or so and it seems to improve everyhing

other than that ive heard seafoam seems to fix things??
 
Low octane fuel helps. It is burned up much easier by the catalytic converters since it ignites at a lower temp than high octane.

New plugs do help (goes back to igniting as much fuel as possible).

Bringing in your car after it has been running for a while (converters are fully heated and working at max capacity).


From what I understand, the smog test is looking for unburned fuel which is comprised heavily of carbon-monoxide.
 
Jared Pabis said:
Bringing in your car after it has been running for a while (converters are fully heated and working at max capacity).
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+1 for making sure you have them cats nice and toasty and for cleaning the MAF.

Not bragging or anything but I just had to take my 4runner and my gf's protege in for the "Test Only gold shield" and my results were amazing! almost nothing showed up....I was even producing less than her 4cly protege.

I don't know about disconnecting the exhaust...im positive they will be able to hear the leak, plus if your failing that bad im sure not fixing the problem will only make the problem worse in the long run.
 
chad99 said:
+1 for making sure you have them cats nice and toasty and for cleaning the MAF.

Not bragging or anything but I just had to take my 4runner and my gf's protege in for the "Test Only gold shield" and my results were amazing! almost nothing showed up....I was even producing less than her 4cly protege.

I don't know about disconnecting the exhaust...im positive they will be able to hear the leak, plus if your failing that bad im sure not fixing the problem will only make the problem worse in the long run.
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They did thw sniff test on my tailpipe whenit was rusted through and mostly disconnect, they didnt notice a thing, it passed NY and CT test 2 days in a row like that. I dont think the NY test sniffed though. But mine wouldnt fail normally.
 
JohnsD90 said:
They did thw sniff test on my tailpipe whenit was rusted through and mostly disconnect, they didnt notice a thing, it passed NY and CT test 2 days in a row like that.
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Why did you have to pass in NY and CT?

To the OP,
Seafoam is still probably better, but I can say I've passed smog in my old '86 22R (after it failed badly) by pouring in a bottle of rubbing alcohol into about a 1/2 tank of gas.
 
brian2sun said:
Why did you have to pass in NY and CT?

To the OP,
Seafoam is still probably better, but I can say I've passed smog in my old '86 22R (after it failed badly) by pouring in a bottle of rubbing alcohol into about a 1/2 tank of gas.
Click to expand...

My dad's work bought it off auction for me and they are a registered dealer, in order for them to sell it to me it had to pass NY for them, so when my dad/me bought it had to pass CT cause thats where we live. My dad works in NY.
 
I have no proof but i read somewhere if you take a spray bottle of water and mist some into the intake it "steam" cleans the pistons and inside of the motor. I dont know if it works or the procedure, and it could be dangerous if you dont know what your doing. I would use seafoam for sure. In the motor, in the gas, in the oil.
 
I concur with getting your cats hot.

Fuel treatment wouldn't hurt.

Plugs/wires... Pretty much everything has been said..

Check and make sure your PCV valve is good.
 
Did your vehicle fail for NOx? Your EGR system controls NOx. If the valve is weak or plugged with carbon, these emissions will be high. And has been said before, make sure its been driven 10-15 miles before testing to get everything up to temp.
 
Plugs and wires were both replaced in Oct 2010 (Actually wires and plugs were replaced in Aug 2010, then plugs were replaced again in Oct because one was faulty). I'm going to go ahead get the oil changed and clean the MAF, and probably run some stuff through the gas lines and such. We'll see what happens.

Thanks everyone for the help!
 
same issue

I have the same exact issue, failed NO for the 15mph test, passed everything else great- although the 25mph NO test was kinda high. Odd that the rpm's are almost the same, around 1600, just slightly higher for the 15mph test. I guess it's testing different loads, at the same rpms. Anyway, anything worked for you? Did it pass? I love my 4runner, a 98 with 250k miles, and do most of the work myself. I'll probably change the plugs, egr valve, clean the MAP, perhaps change the O2 sensor (already did that once a long time ago), and of course, the oil.
 
My '97 barely passed the 2015 smog test on HC. Next test time(2 years later), right before the test I drove it 100 miles, at highway speed, on regular gas and it passed with lower HC's than 2 years previous, which had been done on about a 20 minute pre-test warm up drive.
Note: I always put new plugs in several weeks before the test.
 
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