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The HC and NO emission are very High and fail the smog test on a 1998 dodge ram what can I do to pass.

I replace O2 sensors .

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  • 74 Answers

Sounds like the cat

Posted on Dec 06, 2012

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  • 2 Answers

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Posted on Jan 02, 2017

  • 491 Answers

SOURCE: fails idle emissions test hc

High HC?
****** ignition timing....this will lower HC but raise other values during test.
Do you have room to increase other values?
After test return timing to the most advanced position without spark knock under load for best MPG.

Posted on Aug 11, 2009

  • 834 Answers

SOURCE: failed smog check

How well does the vehicle run?

Assuming that the engine did pass the EGR function test on the emission test results, and the MIL (Malfunction Indicator Light) or check engine light is not on when the engine is running, and if you are not sure when the last time it was that the engine had a complete tune-up, with distributor cap, ignition rotor, spark plugs, spark plug wires, air and fuel filters, then a complete tune-up would certainly help, and if the engine oil and oil filter have not been changed in a while, then they should also be changed before an emission test because long used engine oil traps carbon and it will show up as higher CO on the emission test because the emission analyzer will be able detect the higher CO from the engine oil through the PCV valve.

However, it would seem from those HC readings that there is a vacuum leak, and carefully inspect all of the vacuum lines for any cracks or damage, (especially the vacuum line to the fuel pressure regulator) because cracks in the vacuum lines seem to like to hide underneath the lines.

The emission label under the hood should have the vacuum line routing diagram printed on it, and the vacuum lines should all be checked to be certain that they are all connected correctly.

Here is the firing order diagram for that vehicle to help assist you tune-up the vehicle.


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Posted on Jul 10, 2010

  • 2309 Answers

SOURCE: 93 civic failing emissions test... tested 3 times,

check for any vacuum leaks, run some injector and combustion cleaner through it, check the pcv valve and the egr valve, and fresh oil, can't think of anything else

Posted on Nov 17, 2010

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alicantecoli
  • 22114 Answers

SOURCE: 1993 S10 Chevrolet Blazer DID

what about the air filter is it clean ,silly question i know but you would be surprissed ,does this vehicle have one O2 sensor or two one after the cat as well or is it too old for two O2 sensors ,i know most europeon market vehicles didnt have cats till 1992 and most didnt have two sensors till around 2000 ,also check the two white or two black wires on sensor for 12v these are the heater feed wires for the sensors

Posted on Jan 03, 2011

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Fail smog test


fist i would like you to post the year make and model of the truck along with the HC ppms and NOX ppm it would be very helpful but high hc and nox can be attributed to a faulty EGR system nox is produced when the combustion chamber temperature gets too high so a small amount of exhaust is cycled back into the air stream to help cool them there are other causes but without looking at the levels its much harder to say

Dec 06, 2012 | Cars & Trucks

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I'm barely failing smog due to high hydrocarbons.


Hi Larry, I your position I believe I would take the vehicle for a diagnostic scan and then check the read outs. There could be a problem with any one of a number of sensors but I believe you'll end up with all odds pointing at the cat. Regards John

Aug 25, 2012 | Cars & Trucks

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Failed smog test


Most modern vehicles have 2 catalytic converters, there may be one located at the exhaust manifold, or be what's called a resonator. The resonator will look almost like a cherry bomb muffler, this is a crucial part of exhaust emissions.

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My 1997 Honda Civic failed it's Emissions Test. See below the ASM Emission Test Results. What do you suggest I do to get the car to pass the smog test? ASM Emission Test Results: 15mph - RPM = 1587...


Jose, I don't know if this will give you the answer you are looking for because there are many things to consider here. The exhaust gas recirculation valve (EGR) is one of the main things involved in reducing NO emissions. This valve is controled by the power control module. (PCM) This is your vehicles computer. The PCM monitors the vehicles speed and will command the EGR to open when the vehicle attains a certain speed, which is why the ASM test being done is recorded at two different speeds. At 25 MPH your vehicle failed the hydrocarbon (HC) emissions limit and this could be for a number of reasons. When is the last time you car was tuned up? Old spark plugs, wires, clogged air filters, oxygen sensors, leaking injectors (personal experience) or the PCV valve could be contributing to the results of the test. I guess that the easiest way to go is to tune up the engine replacing the spark plugs, wires, air filter and the PCV valve and don't forget to have the oil changed at the same time. Only then should have the vehicle retested and see what the results are. Should it fail again you may have to consider having the EGR or the catalytic converter replaced depending on what portion of the test fails. If the NO fails I would consider the EGR. If the HC fails then I would consider the catalytic converter. Good luck with this.

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1 Answer

1991 Honda Accord LX failed emission test on smog test. High CO and HC on 25mph


not enough info. Typically, CO and HC together can be the result of poor fuel control or misfire, or worn components such as O2 sensor or catalytic converter, but without more data, repair recommendations are likely to waste money and not achieve success.

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