Help!! Car won't pass smog for the 3rd time
02-02-2012, 08:23 PM
#21
I keep reading that brand new coated headers can foul the O2 sensors as the coating burns off or cures inside the pipes. You're supposed to use old O2 sensors for a while then switch to new sensors with new coated headers. Are your new emissions legal headers coated?
Don't they give you a 'pass' after you've spent a certain amount of dollars on trying to get it to pass? I think in the old days that's what they did.
Don't they give you a 'pass' after you've spent a certain amount of dollars on trying to get it to pass? I think in the old days that's what they did.
Last edited by guppymech; 02-02-2012 at 08:28 PM.
02-02-2012, 10:14 PM
#22
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I keep reading that brand new coated headers can foul the O2 sensors as the coating burns off or cures inside the pipes. You're supposed to use old O2 sensors for a while then switch to new sensors with new coated headers. Are your new emissions legal headers coated?
Don't they give you a 'pass' after you've spent a certain amount of dollars on trying to get it to pass? I think in the old days that's what they did.
Don't they give you a 'pass' after you've spent a certain amount of dollars on trying to get it to pass? I think in the old days that's what they did.
02-03-2012, 08:14 AM
#23
It looks like high NOx with nothing else out of the ordinary. High combustion temp while not running lean points to too much timing advance or non-functional EGR. The valve is new so, is the EGR solenoid working right and getting proper manifold vacuum? Are the passages clear of carbon buildup? If all of that checks out, I'd head after the pcm programming.
Some alcohol in the fuel tank would bring the combustion temps (and NOx readings) down some for sure, if that is all you are after. Beat the **** out of it for 10 minutes before you line up for the test. The higher the cat temp, the better.
Some alcohol in the fuel tank would bring the combustion temps (and NOx readings) down some for sure, if that is all you are after. Beat the **** out of it for 10 minutes before you line up for the test. The higher the cat temp, the better.
02-03-2012, 12:05 PM
#24
When HC are high it helps cool the combustion chamber bringing Nox down. You fixed the HC problem but now have high Nox because there isn't the extra fuel cooling the combustion chamber. When my car had headers and stock motor I always failed on Nox too. The EGR system is back pressure sensing and does not function properly with headers. Put all the vacuum in the world to the valve without back pressure it will not open. I used to manually lift the EGR valve open during the test because I had a friendly inspector!
02-03-2012, 06:43 PM
#25
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When HC are high it helps cool the combustion chamber bringing Nox down. You fixed the HC problem but now have high Nox because there isn't the extra fuel cooling the combustion chamber. When my car had headers and stock motor I always failed on Nox too. The EGR system is back pressure sensing and does not function properly with headers. Put all the vacuum in the world to the valve without back pressure it will not open. I used to manually lift the EGR valve open during the test because I had a friendly inspector!
02-03-2012, 06:54 PM
#26
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we have similar setups and I just failed for too high of CO at idle and 2500rpm. I just had a full tune up done also, injectors,plugs,wires,opti,fuel filter. car has a cat, i dont know wtf to do next.
02-06-2012, 09:02 AM
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Does that top end cleaner actually work? Also, I get fairly strong exhaust smell in the cabin. When I did my emissions testing, it was cold out and they closed the bay doors. I pretty much stunk out the place with exhaust fumes.
02-06-2012, 11:53 AM
#32
02-06-2012, 12:13 PM
#34
Here is a decent tech article about them (mostly covers negative backpressure) - http://www.tomco-inc.com/Tech_Tips/ttt27.pdf
Another (more basic but touches on negative and positive) - http://www.howstuffinmycarworks.com/EGR_valve.html
If the valve has an "N" on it it is a negative backpressure. If it has a "P" on it, it is positive backpressure. Oddly, I have seen both on different LT1s.
02-06-2012, 12:37 PM
#37
The specific recollection I was referring to was an instance where GM tech assist had me switch an Impala SS from a negative backpressure valve to positive. I then started looking at them on cars I serviced and didn't find a rhyme or reason as to what car had what valve on it.
02-06-2012, 12:58 PM
#38
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Yep, sure does.
Here is a decent tech article about them (mostly covers negative backpressure) - http://www.tomco-inc.com/Tech_Tips/ttt27.pdf
Another (more basic but touches on negative and positive) - http://www.howstuffinmycarworks.com/EGR_valve.html
If the valve has an "N" on it it is a negative backpressure. If it has a "P" on it, it is positive backpressure. Oddly, I have seen both on different LT1s.
Here is a decent tech article about them (mostly covers negative backpressure) - http://www.tomco-inc.com/Tech_Tips/ttt27.pdf
Another (more basic but touches on negative and positive) - http://www.howstuffinmycarworks.com/EGR_valve.html
If the valve has an "N" on it it is a negative backpressure. If it has a "P" on it, it is positive backpressure. Oddly, I have seen both on different LT1s.
Well according to shoebox the negative BP EGR does indeed use exhaust back pressure to aid in its correct operation. Looks like we're both wrong:
http://shbox.com/1/4th_gen_EGR.html
Oopsie. You were a tech?
02-06-2012, 01:46 PM
#39
Well according to shoebox the negative BP EGR does indeed use exhaust back pressure to aid in its correct operation. Looks like we're both wrong:
http://shbox.com/1/4th_gen_EGR.html
Oopsie. You were a tech?
http://shbox.com/1/4th_gen_EGR.html
Oopsie. You were a tech?