Failing smog checks


Old 03-21-11, 07:49 PM
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Join Date: Mar 2011
Location: USA
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Question Failing smog checks

This is the best information I found on the web so far. Im tired of finding the same answers that are not clear. Im failing smog miserably. Replaced spark plugs, spark plug wires, O2 sensor, Catalytic Converter, ECT sensor, thermostat and new coolant. Failed smog 3 times now and only passing the 25 mph test. My car is a 1995 Honda Prelude Si Vtec. I took apart the intake manifold, cleaned it up with the EGR valve and the ports. My timing is dead on at the factory specs. Fans are working also. What is a DSO and where can i get one to check lean/rich fuel mixture. I had a check engine light code also, it was the EGR Valve, once it cleaned it and replaced the EGR solenoid and EGR vacuum control unit, it went away. My MAX at 15 mph test for NOx is 493 and im measuring 822. what else can i do to get it to pass smog?


Last edited by the_tow_guy; 03-22-11 at 07:58 AM.
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Old 03-22-11, 07:58 AM
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Moved you out of that 7 year old thread to a fresh thread.
Old 03-22-11, 01:52 PM
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I can help you. There are a number of reasons why your NOx numbers are so high. I need you to take your time reading what I’m about to write. I’m letting you know ahead of time that this is going to be a long answer. Please take your time reading and understanding my response. You will have to answer a number of questions. If you don’t understand the question or terminology being used, then let me know. I’m going to keep it basic and fundamental. Does your car?

Have an aftermarket, non vehicle specific, universal, fresh air intake installed?
Have aftermarket, non vehicle specific, universal headers installed?
Have aftermarket non vehicle specific universal nitrous oxide installed?

Next is the misconception that the timing on your car is adjustable. The timing on your car is not adjustable. The “PCM” sets, adjusts, and re-adjusts the timing according to engine and vacuum load. The bolts you see holding down the distributor are there only to loosen if the distributor if it needs to be replaced. If you loosened those bolts, and readjusted the distributor’s normal resting position, that could be the reason why the engine is failing the smog test.

Next are all the parts you replaced. Why did you replace them in the first place? Did you check them first, or did you just replace them? Did you know that you must use “OE” emission parts for your particular vehicle and engine? Items like universal catalytic converters and oxygen sensors will cause issues in your particular vehicle and engine. Has the fuel filter been changed recently?

Have you ruled out engine misfires?
Engine vacuum leaks?
Exhaust system leaks?
Ambient air issues?
Old 12-22-11, 01:11 PM
Join Date: Dec 2011
Location: USA
Posts: 1
" universal catalytic converters and oxygen sensors will cause issues in your particular vehicle and engine"

This is a huge issue, especially if you live in CA . What would be super helpful, is if there was a specific numeric rating system, that could somehow tell you ahead of time at what levels it functions in regards to all 3 gases. Any one with helpful information on this would greatly be appreciated.
The idea of a catalytic converter being CA Legal still eludes me, if I am looking at a catalytic conveter how can I tell?
Old 01-03-12, 12:59 PM
Join Date: Jul 2009
Location: Ca
Posts: 191
How about listing the other gases you passed on. HC, CO, CO2, O2. that might help with diagnois's.

Your cat should have a number stamped on it that can be looked up to see if it it CARB compliant.


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