Help!! Car won't pass smog for the 3rd time
02-02-2012, 11:21 AM
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Help!! Car won't pass smog for the 3rd time This is getting expensive and ridiculous. Quick back ground. I had long tubes on my 95 z28 all stock. It was time for smog so I took the off and put on some legal california mid length headers,
Took the car to get smogged and it didn't pass because of high HC (and nothing else everything else was perfect), I was told to give it a tune up, so I did. new plugs, wires, and o2 sensors.
Second time it didn't pass. I was told it needed a new opti and water pump. So I replaced those. With the second smog it was high HC again but it did drop.
Now I put in a new opti, water pump, and more new plugs because some of the plugs burned on the headers. Took it to the shop today and this time it was high NO. This was never a problem with the other smogs test.
At 15 mph max is 483 I had 784
At 25 mph max is 494 I had 742
With my other two smog test my NO was under 230 for both test. Now its so high, Im totally confused. Can anyone help out, what can cause a high HC all of a sudden??
Took the car to get smogged and it didn't pass because of high HC (and nothing else everything else was perfect), I was told to give it a tune up, so I did. new plugs, wires, and o2 sensors.
Second time it didn't pass. I was told it needed a new opti and water pump. So I replaced those. With the second smog it was high HC again but it did drop.
Now I put in a new opti, water pump, and more new plugs because some of the plugs burned on the headers. Took it to the shop today and this time it was high NO. This was never a problem with the other smogs test.
At 15 mph max is 483 I had 784
At 25 mph max is 494 I had 742
With my other two smog test my NO was under 230 for both test. Now its so high, Im totally confused. Can anyone help out, what can cause a high HC all of a sudden??
02-02-2012, 01:13 PM
#5
What were the O2, HC, CO and NOx readings?
O2 is unconsumed oxygen
HC is unburned fuel
CO is partially burned fuel
NOx is a byproduct of high combustion temperature
The levels of all four gasses taken together provide a snapshot of what is going on inside the combustion chamber. Taken individually, they really don't say much.
O2 is unconsumed oxygen
HC is unburned fuel
CO is partially burned fuel
NOx is a byproduct of high combustion temperature
The levels of all four gasses taken together provide a snapshot of what is going on inside the combustion chamber. Taken individually, they really don't say much.
02-02-2012, 01:41 PM
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02-02-2012, 01:49 PM
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As you can see here this was my previous smog test. the NO was fine but the HC didn't pass. Fast forward to new plugs, wires, opti, water pump, o2 sensors, CAT, and now I have a new EGR I'm about to put in...what else can I do??
02-02-2012, 02:01 PM
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If you consider a plugs, and wires a tune, then that all Ive done...but now that I think about it. When the car had LT headers a shop did do some kind of tune to it to make it run somewhat "better"...would the computer still think it has LT headers or something??
02-02-2012, 02:22 PM
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The cat is about 5 months old. With less than 100 miles on it. Im in cali and seems like smog shops won't look the other way anymore. everyone now is going by the book...lol.
02-02-2012, 05:41 PM
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Try new o2 sensors.
Add a gallon of e85 with several gallon of super unlead.
The alcohol will reduce combustion temps to bring down "NO" and the new o2 sensor will allow the ecu to adjust the parameter faster, reduce the "HC"
Cliff
369 CP Chevelle
Add a gallon of e85 with several gallon of super unlead.
The alcohol will reduce combustion temps to bring down "NO" and the new o2 sensor will allow the ecu to adjust the parameter faster, reduce the "HC"
Cliff
369 CP Chevelle
02-02-2012, 07:32 PM
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i have not personally done this as i just have to pass the idiot light test, but my buddy in his early model 5.0 mustang had to pass the sniffer test since it was earlier than 96. he dumpped 2 cans of denatured alcohol from depot in the tank when he filled it up and passed everytime. make sure the cats are good and hot too. go for a solid 30 minutes drive before you take it in. best of luck
02-02-2012, 07:39 PM
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02-02-2012, 08:06 PM
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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.
