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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

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Old 11-02-2007, 10:28 AM   #1
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Failed Emissions Inspection. Causes of high NOx?

1995 3VZE, 139519 miles.

I failed my emissions inspection for the fourth time today. Each time it has been because of high NOx. I've already checked my EGR and can't find anything wrong. I cleaned the EGR valve after failing the third time, and I can hear the valve activating when I apply vacuum to it. All of the vacuum lines are connected properly and all appear fine after visual inspection. What are other causes of high NOx I need to be checking into?

Here are the last two inspection reports, just FYI.

10-18-07
High Speed Results (25mph)
Standard: 956
Current: 1268

Low Speed Results (15mph)
Standard: 1046
Current: 1250


11-02-07
High Speed Results (25mph)
Standard: 956
Current: 1419

Low Speed Results (15mph)
Standard: 1046
Current: 1400


Looking at the numbers, the NOx has actually gone up after cleaning the EGR valve. HELP!!! This is pissing me off to no end.
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Old 11-02-2007, 11:50 AM   #2
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Aren't the Texas Emissions test a PITA. I have had problems getting my Jeep to pass lately and though I don't know if this will help you might the the following.

I think NOX is related to the Cat but I am not sure...anyway, try this.

1) If the Plugs are old, change them.

2) Change the oil

3) Get some GTP..."guaranteed to pass" and put it in the gas tank...(if possible, fill up with Chevron gas.

4) Drive on the freeway for 20 or 30 miles to get the Cat hot, get the GTP in the intake, and blow all the crap out.

5) Then take it in for inspection...make sure the engine is hot...don't let it sit and cool down.

This may help alot...especially if you do a lot of stop and go driving...however if the CAT is real bad, it may not help.

Good luck....

I just converted my Jeep to MPI (multiport fuel injection) after it continued to fail...high CO and CO2. I am going to replace the tailpipe this weekend and try the inspection again. Like yours, mine got continually worse...I am thinking it was building up hydrocarbons in the oil.
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Old 11-02-2007, 12:18 PM   #3
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How old is your cat? If its original you might want to take this as the time to upgrade your exhaust.
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Old 11-02-2007, 01:40 PM   #4
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My truck failed on Nox due to malfunctioning PCV valve you might try that...
note- I already had a new cat before the test, you may need to change that also...
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Old 11-02-2007, 04:29 PM   #5
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I know theres arlready a Seafoam thread, but I can't help but think that would hlep clean up the emissions.

I think high NOx is caused by excessive combustion temp. Could be carbon deposites (Seafoam it).

Hope this helps.
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Old 11-02-2007, 04:37 PM   #6
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check for vacume leakes also. it woud make you run lean and bring your cylinder temps up to 2500f to cause nox.
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Old 11-02-2007, 04:53 PM   #7
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oh crap, im up for a smog too! i gota 95 and live in cali... god speed to me.

waiting on seafoam.
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Old 11-02-2007, 04:55 PM   #8
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What were your other readings at the time?

Have you done an integrity check of the rest of the systems?
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Old 11-02-2007, 05:04 PM   #9
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Try dropping your fuel level to 1/2 tank and then adding 2 gallons of E85 fuel. The ethanol will reduce NOx and HC values.
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Old 11-02-2007, 05:06 PM   #10
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Running lean will do this everytime.
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Old 11-14-2007, 05:06 PM   #11
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To add to the problem, I now have a CEL code 26. AIR/FUEL RATIO RICH INDICATOR.

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Any suggestions?
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Old 11-15-2007, 05:23 AM   #12
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I had a code 26 once and it ended up being my fuel regulator. when i applied vacuum to the port it didnt hold. regulator was leaking from somewhere. Check your vac hoses leading to the regulator and check the vsv as well.
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Old 11-15-2007, 05:55 AM   #13
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looks like you and i are in the same boat my "no" readings got higher also did the seafaom thing checked egr and pcv both working fine i did repace the exhaust from the cat back ( not including the cat) and my readings are getting worse plugs and wires are fine ugggggggggg im going to buya cat today!!!!!!!!!!!!
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Old 11-15-2007, 09:26 AM   #14
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I may have already asked in another thread, did you change the O2 sensor?

Changing the cat is a good idea.
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Old 11-15-2007, 03:38 PM   #15
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connect a vacuum guage to the EGR vacuum hose and goose the throttle with the engine running at normal operating temperature. you should see about 5-10" vacuum. pump the egr valve up with 10" vacuum with the engine idling. it's should stall or run bad enough that you think it will stall.

check the ignition timing.

Make sure it is not running too hot.
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Old 11-15-2007, 04:00 PM   #16
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Yep, EGR controls NOx, make sure it is working 100%, all lines unplugged, exhaust gas passages open, modulator working, etc. Then new cat can help, retarding timing 3-5 degrees can help, premium gas can help.
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Old 11-15-2007, 04:36 PM   #17
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ill let everyone know but after the egr check the pcv check seafoam and a new muffler i just put a new cat on i know its not my thread but im in the same boat i have new cat installed today so we will see what happens tomarrow thank gawd ohio doesnt charge for emissions test
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Old 11-21-2007, 03:36 PM   #18
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emissions problem

Had the same problem, after a new cat, seafoam, throtle body cleaning and cleaning the EGR, it still didn't pass, it turned out to be a cracked vaccum line, replaced it and passed with no problems.
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Old 11-21-2007, 03:36 PM
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