Honda Accord (1990 - 2002) Includes 1997 - 1999 Acura CL

Accord 93 Failed Smog Test High HC & NO

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Old Jul 2, 2012 | 04:02 PM
  #1  
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Default Accord 93 Failed Smog Test High HC & NO

Need help please.

here are my readings
15mph co2 14.9 o2 0.1 HC max 61 meas 107 CO max 0.51 meas 0.26 NO max 490 meas1137

25mph co2 15.3 o2 0.0 HC max 36 meas 53 CO max 0.49 meas 0.05 NO max 730 meas 316

Anyone please help!!!!!!!!!!!!!!
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Old Jul 2, 2012 | 06:53 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Originally Posted by rigoi

Anyone please help!!!!!!!!!!!!!!
Toyota 4-5 gas pdf

This is a great PDF for anyone who has to smog. Read it, Learn it, Love it.

Originally Posted by rigoi
15mph
co2 14.9
o2 0.1
HC max 61 meas 107
CO max 0.51 meas 0.26
NO max 490 meas1137

25mph
co2 15.3
o2 0.0
HC max 36 meas 53
CO max 0.49 meas 0.05
NO max 730 meas 316

Last edited by MAD_MIKE; Jul 2, 2012 at 07:14 PM. Reason: for easy reading
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Old Jul 2, 2012 | 07:19 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

When was the last time the car had a full on tuneup?
Plugs, wires, O2(not beer can bosch type) yadda yadda?
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Old Jul 2, 2012 | 08:52 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Before I tested the car I change the plugs and change the oil. Today I bought new wires, dist.cap and new rotor. I have never chaged the O2 sensor.
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Old Jul 3, 2012 | 12:35 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

That link Mike posted looks great. I will add that normally high NOX and high HC is a result of an EGR valve and EGR passages that need to be cleaned out.
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Old Jul 3, 2012 | 12:38 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

ive seen this on several cars too. and the owners go doing tunes up o2 etc. when ive found it was a stuck open thermostat failing them and giving them high hc & no.
Originally Posted by rigoi
Before I tested the car I change the plugs and change the oil. Today I bought new wires, dist.cap and new rotor. I have never chaged the O2 sensor.
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Old Jul 3, 2012 | 07:09 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

I clean out the passages yesterday and they look good. Change the thermostat before doing the smog check. How could I check to see if it's stuck?
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Old Jul 3, 2012 | 07:51 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

IF ITS NEW I DONT THINK IT WOULD OF FAILED. ONLY WAY IS TO TAKE IT BACK OUT AND WARM IT UP A COUPLE OF TIMES IN IN A POT AND SEE IF IT EVER GETS STUCK OPEN
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Old Jul 3, 2012 | 10:35 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Originally Posted by jdmcertified909
ive seen this on several cars too. and the owners go doing tunes up o2 etc. when ive found it was a stuck open thermostat failing them and giving them high hc & no.
A stuck open thermostat will not increase NOx or HC
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Old Jul 3, 2012 | 10:37 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Is the car misfiring?? If I remember running lean can cause both high HC and high NOx
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Old Jul 3, 2012 | 10:40 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Originally Posted by rigoi
Need help please.

here are my readings
15mph co2 14.9 o2 0.1 HC max 61 meas 107 CO max 0.51 meas 0.26 NO max 490 meas1137

25mph co2 15.3 o2 0.0 HC max 36 meas 53 CO max 0.49 meas 0.05 NO max 730 meas 316

Anyone please help!!!!!!!!!!!!!!
Looks like a bad cat.
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Old Jul 3, 2012 | 11:50 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

yeah, I would replace the cat now.
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Old Jul 3, 2012 | 11:51 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

yes it does a cold non normal operating temperature car will burn more gas thats what the ect is for. it reads the coolant temp and send data to the ecu for rich or lean conditions. not only have i seen this on hondas but specially on muscle. like a camaro i worked on. it wasnt passing smog and i seen that the stat was open all the time not allowing motor to get hot enough i told him to change the stat he didnt believe me that it was that. so he took it payed $500 for each cat this camaro had two cats plus labor total he said he paid $1700. and it still didnt pass. and the cats were original. it had the same high hc & no the new cats didnt help at ALL. so HE bought the thermostat changed it him self and took it back in and it passed right away
Originally Posted by DCFIVER
Looks like a bad cat.
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Old Jul 3, 2012 | 11:53 PM
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Default Re: Accord 93 Failed Smog Test High HC & NO

and would you also plz explain why your calling me a liar? when its from my own experience? from what i have seen. from what i have actually fixed. and seen them pass after the new t stat was put in?
Originally Posted by DCFIVER
A stuck open thermostat will not increase NOx or HC
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Old Jul 4, 2012 | 12:00 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Originally Posted by DCFIVER
Looks like a bad cat.
Originally Posted by holmesnmanny
yeah, I would replace the cat now.
cats really dont go bad by themselves...they usually go bad because something makes them go bad...so it would be best to fix what made it go bad in the first place
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Old Jul 4, 2012 | 12:21 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

he's got an old car, dude. Cats do eventually wear out.
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Old Jul 4, 2012 | 09:20 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Originally Posted by jdmcertified909
yes it does a cold non normal operating temperature car will burn more gas thats what the ect is for. it reads the coolant temp and send data to the ecu for rich or lean conditions. not only have i seen this on hondas but specially on muscle. like a camaro i worked on. it wasnt passing smog and i seen that the stat was open all the time not allowing motor to get hot enough i told him to change the stat he didnt believe me that it was that. so he took it payed $500 for each cat this camaro had two cats plus labor total he said he paid $1700. and it still didnt pass. and the cats were original. it had the same high hc & no the new cats didnt help at ALL. so HE bought the thermostat changed it him self and took it back in and it passed right away
Still wrong...
Originally Posted by jdmcertified909
and would you also plz explain why your calling me a liar? when its from my own experience? from what i have seen. from what i have actually fixed. and seen them pass after the new t stat was put in?
I did not call you a liar. I said you were wrong. You have minimal to no understanding of exhaust gas analysis and you simply connected the dots during an event you did not comprehend. Many "mechanics" do it all the time.You are wrong. Period.


The exhaust gas readings that the OP put up speak for themselves. It quite obviously needs a cat. But you do not understand what you are reading and are incapable of making the proper interpretation, same way you think a stuck open thermostat will raise NOx...
Originally Posted by wolfy47
cats really dont go bad by themselves...they usually go bad because something makes them go bad...so it would be best to fix what made it go bad in the first place
The noble metals in cats do actually degrade as a natural progression. Particularly in substandard after market cats.
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Old Jul 4, 2012 | 11:42 AM
  #18  
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Default Re: Accord 93 Failed Smog Test High HC & NO

One of the wires on the temp. sensor on the upper radiator hose had broken off. Could that of cause the car to run lean?
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Old Jul 4, 2012 | 10:30 PM
  #19  
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Default Re: Accord 93 Failed Smog Test High HC & NO

so your saying that the camaro after a FULL tune up and two brand spanking new cat and still not passing is just me? but after the thermostat change it passed thats still just me? so when an engine is cold it doesnt throw more gas becuz its telling the ecu its cold so its running rich? and gas getting passed thru cats and unburnt fuel? so thats not the reaon of high hc & no? mmmmmmmmmm interesting. wish i still had that print out he gave me after the brand new cats were installed. the numbers of high hc & no decreased by a hair. but when the thermostat was changed it passed. with flying colors. unburnt fuel is hc but ok. i believe proof more then i believe people especially if i seen it with my own eyes.... but w/e not going to argue with you.
Originally Posted by DCFIVER
Still wrong...

I did not call you a liar. I said you were wrong. You have minimal to no understanding of exhaust gas analysis and you simply connected the dots during an event you did not comprehend. Many "mechanics" do it all the time.You are wrong. Period.


The exhaust gas readings that the OP put up speak for themselves. It quite obviously needs a cat. But you do not understand what you are reading and are incapable of making the proper interpretation, same way you think a stuck open thermostat will raise NOx...

The noble metals in cats do actually degrade as a natural progression. Particularly in substandard after market cats.
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Old Jul 4, 2012 | 10:35 PM
  #20  
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Default Re: Accord 93 Failed Smog Test High HC & NO

the one thats on the housing right?? if correct thats your ect sensor *engine coolant temp sensor* thats what tells your computer what temp the coolant is. and it either makes it rich or lean. but i cant remember which it is if its not completing a circuit. i would say yes im not in shop right now to look it up im at home. but i believe that yes a non complete circuit would be lean condition.
Originally Posted by rigoi
One of the wires on the temp. sensor on the upper radiator hose had broken off. Could that of cause the car to run lean?
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Old Jul 6, 2012 | 03:28 AM
  #21  
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Default Re: Accord 93 Failed Smog Test High HC & NO

I believe when the car is cold it runs rich. That's why you get excessive HC when the thermostat is stuck in open position.
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Old Jul 6, 2012 | 03:29 AM
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Default Re: Accord 93 Failed Smog Test High HC & NO

Originally Posted by rigoi
One of the wires on the temp. sensor on the upper radiator hose had broken off. Could that of cause the car to run lean?
That switch only controls the fans when it's really hot and the car is turned off.
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