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Discussion Starter #1
A month ago I took my truck to get it smoged and failed miserably. In fact, my truck was considered a "gross polluter".

I replaced a few things (one VSV, EGR valve and modulator, vaccum hoses) and at least the check engine light went away. I did complete tune-up and headed to the smog station again and failed again at 15mph only. I asked them to do a diagnosis but couldn't find anything wrong.

But the guy suggested replacing the Cat which I probably will do (its been 4 years since it was replaced) and about 99K miles.

I have an aftermarket air intake which the mechanic said could be a problem. Not because it is an aftermarket system, but because it sits pointing down and sideways. He thinks the flapper in the Air Flow Meter may not be moving freely.

I am gonna try to post a picture of the emissions report to see if anyone has any idea what could be wrong.

Any help would be appreciated.
 

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Discussion Starter #3
emissions

That is my plan. I will adjust the air meter first and re-test since the test shop is one of those "pass or re-test free". If it doesn't pass then I'll move on to replace the cat.

Thanks for the advice.
 

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Supafly
1991 toyota pickup
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4,401 Posts
If you can, post up your results for all the feilds. Usually if say your o2 sensor is bad, it will effect your results in the other sections. Mine failed with high nox, all other sections VERY low. Thus the EGR valve is the culprit.

But say your HC are pretty high, an o2 sensor might be causing some trouble.

Also if you can, unbolt the cat (if its an oem style) or remove it and check the screens. If they are damaged get a 80 dollar highflow magnaflow.
 

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Discussion Starter #5
emissions

I don't see an option to post pictures anymore, so I don't know how to go about it.

But yes, I got high readings on the nox. Based on what you are saying the culprit is the EGR valve. The guys doing the diagnostics said it was ok, but they could be wrong. I checked it myself as indicated in the service manual and does what it is supposed to do.

If you know how to post a pix let me know.
 

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Discussion Starter #8
results

Here is what the report spitted out:

--------------HC(PPM)------ CO(%)------NO(PPM)
Test---RPM max ave mea max ave mea max ave mea
15mph 1655 127 34 180 0.78 0.11 0.61 1031 260 1795 FAIL
25mph 2685 108 23 79 0.99 0.10 0.36 891 217 788 PASS

A second person told me today it is the EGR and that many times testing it according to the service manual doesn't really tell you if it is damaged or not.

What do you think?
 

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YOTA Master
'93 2wd P/U
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2,434 Posts
Make sure your ignition timing is correct.

The High NOx could be attributed to advanced timing as well as EGR problems.

The egr valve may be working but the passage in the head could be restricted

a lazy O2 could also cause problems like that. at lower speeds it may not be hot enough then later in ther test at a higher rpm it may work better.

really you need to test these systems to find the culprit.
 

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Surfing TN via iPhone
05 Tacoma DC 4x4 TRD
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Try to stick with Denso. Some Toyotas don't like Bosch sensors.
 

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Discussion Starter #16
emissions

Thanks for your feedback.

I just cleaned the EGR and will replace the O2 sensor this week to get it retest it. I'll keep the posting updated.
 
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