88 Honda Acord did not pass knox for smog?

Question

Can anyone help me Ca kills everyone with an older car to pass smog. I passed everything except knox by just a little, any suggestions on what to do

Answer 1

Honda Guy's answer is 100% dead on!

Knox is created by heat in the combustion chamber so check the EGR operation first.



What I want to add is...The other cause of higher combustion chamber temperatures is compression ratio. Where I'm going with this is there could be an excessive amount of carbon buildup on top of your piston's. If there's a build up of carbon it will actually increase the compression ratio since the carbon ultimately takes up space in the combustion chamber which squeezes the air/fuel harder which creates a harder explosion which creates more heat.

So if the EGR system is operating, try a product called Sea Foam or go to a good shop and get an 'Air Induction Service'. Both will clean out the carbon in the Intake and combustion chamber.

Here's another problem and I dont want to discourage you. You could do all of this and the knox could hit near zero but then the HC or Co2 could go way up because you could have 2 problems. Like a rich running engine masked by a non operating EGR system.

It happens!

When the U.S. EPA started measuring Knox in exhaust emissions in 1972 it killed the Muscle Car era because the higher the knox the lower the HC and Co2.

Detroit was pumping out high compression engines because they thought knox were good because it lowered HC and Co2. Enter EGR systems, lower compression ratio's and smaller/leaner carbs.............    

Answer 2

If its carburated, get a few bottles of heat(alcohol) and pour into an almost empty tank of gas, Drive the car hard(get it hot) to the test site, this should allow you to pass assuming you missed by a few PPM... You can try this if it is fuel injected too, but the results wont be the same as with a carb.

Answer 3

I have to take issue with the other response as it is high combustion temperatures that cause NoX to form.

the usual cause of high NoX is an inoperative EGR valve.  The EGR routes inert exhaust gas into the intake manifold to be mixed in with the incoming air.  Inert means they won't burn; the exhaust gas basically takes up space that oxygen rich air would otherwise fill.  because there is less oxygen available for combustion the cylinder temperature will be reduced and NoX will not form.

find out why your EGR isn't working.  it could be that the passage that the exhaust gasses pass through is choked with carbon (like soot in a chimney or plaque on an artery).  I could be that the valve doesn't work at all because of a vacuum leak to the valve or that the valve is simply dead after 20 years.

regardless, if you passed the other tests and just failed NoX its typically the EGR valve thats at fault.  the only other item would be a diminished or deteriorated catalytic converter.  the catalytic converter is a possibility if all readings are high but i'd find out about the EGR first as the reduction of NoX is the only reason that valve is on the engine.

also check anything that would cause the engine to run hot--low coolant level, over-advanced ignition timing etc. as they could also cause excessive emissions

hope that helps