Failed Emission / Aircare ?
07-21-2007, 02:18 PM
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Failed Emission / Aircare ?
OMG, I can't believe it... for the first time in my life (and with the shark), I failed the emissions test this morning! 
For some reason my NOX level was a bit higher than allowed... very odd... it has always passed with flying colours with little or no traces... everything else on the test pretty much showed no or trace emissions... so now here's the question... what could cause this?
Something popped into my mind that could be a brain lapse and I only remembered after I went through the test... could Swepco fuel system cleaner do this? If I recall, the tank of gas currently in my car atm has that stuff in it... if this is the case, then ugh <smacks head>
So, how's all you rennlisters this morning?
For some reason my NOX level was a bit higher than allowed... very odd... it has always passed with flying colours with little or no traces... everything else on the test pretty much showed no or trace emissions... so now here's the question... what could cause this?Something popped into my mind that could be a brain lapse and I only remembered after I went through the test... could Swepco fuel system cleaner do this? If I recall, the tank of gas currently in my car atm has that stuff in it... if this is the case, then ugh <smacks head>
So, how's all you rennlisters this morning?
07-21-2007, 02:25 PM
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Post your numbers or your chart so that we can see them.
What is the age of your 02 sensor? Your MAS? Have your injectors ever been cleaned?
If HC and CO were very low and only NOx was high then I would suspect either Cats or carbon buildup. We had a local auto 928 that could not pass emissions with all new everything (02, cats, etc.) until it was de-carb'd with the BG treatment. The de-carb cut the NOx in half. (And I suspect would have cut it further but (also a suspicion) I think only half if the engine was cleaned.)
What is the age of your 02 sensor? Your MAS? Have your injectors ever been cleaned?
If HC and CO were very low and only NOx was high then I would suspect either Cats or carbon buildup. We had a local auto 928 that could not pass emissions with all new everything (02, cats, etc.) until it was de-carb'd with the BG treatment. The de-carb cut the NOx in half. (And I suspect would have cut it further but (also a suspicion) I think only half if the engine was cleaned.)
07-21-2007, 02:48 PM
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What is the "BG treatment?" There's a radio show that comes on Saturdays and the guy is always talking about BG products. The white trash way to de-carb an engine is to run it up to normal operating temperature and then SLOWLY pour water into the intake. You have to pour it slow enough to keep the engine running.
07-21-2007, 04:13 PM
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My '87 S4 did the same thing some years back. I was told by my maintenance shop that they would have to "tweak" the engine to see if they could improve the Nox rating. If that didn't work they said I probably would need a new catalytic converter. By the way, it did work whatever they tweaked and I had to take it back afterwards so they could set everything back to factory specs. Good luck!
07-21-2007, 04:22 PM
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When mine did this I replaced the caps/ rotors/o2 sensor/plug wires and passed okay. I suspect cats will be required before the next one.
07-21-2007, 09:42 PM
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The chart shows the relationship of engine exhaust, converter efficiency and tailpipe emissions during testing. Both too rich or too lean can cause emission failures.
HC CO NOx Possible Cause or Recommended Action
High High High Replace converter and O2 sensor; verify tune-up and correct any faults
High Low High Replace converter, tune-up & check lean AFR, leaking exhaust valves
Low High High Replace converter and O2 sensor
High High Low Rich AFR, air injection
High Low Low Run-in converter, tune-up, oil change
Low Low High EGR, lean AFR, leaks, run-in converter, use larger converter
Low High Low O2 sensor, rich AFR
Low means less than the test fail point; high means near or above the test fail point.
It's also very important that your 928 is up to operating tempertures or better still HOT.
Jim Mayzurk
93 GTS 5-spd
HC CO NOx Possible Cause or Recommended Action
High High High Replace converter and O2 sensor; verify tune-up and correct any faults
High Low High Replace converter, tune-up & check lean AFR, leaking exhaust valves
Low High High Replace converter and O2 sensor
High High Low Rich AFR, air injection
High Low Low Run-in converter, tune-up, oil change
Low Low High EGR, lean AFR, leaks, run-in converter, use larger converter
Low High Low O2 sensor, rich AFR
Low means less than the test fail point; high means near or above the test fail point.
It's also very important that your 928 is up to operating tempertures or better still HOT.
Jim Mayzurk
93 GTS 5-spd
07-21-2007, 10:24 PM
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Originally Posted by JHowell37
What is the "BG treatment?" There's a radio show that comes on Saturdays and the guy is always talking about BG products.
https://rennlist.com/forums/showthre...6&page=2&pp=15
The white trash way to de-carb an engine is to run it up to normal operating temperature and then SLOWLY pour water into the intake. You have to pour it slow enough to keep the engine running.
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07-21-2007, 10:29 PM
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Originally Posted by Jim M.
HC CO NOx Possible Cause or Recommended Action
High Low High Replace converter, tune-up & check lean AFR, leaking exhaust valves
High Low High Replace converter, tune-up & check lean AFR, leaking exhaust valves
07-22-2007, 07:11 AM
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If everything else is in line then most likely the cat is working as it should. Take a look at the O2 sensor.
From inside the car disconnect the O2 sensor's big plug. With clip leads connect a VOM and set to the low voltage scale - probably 2 volts DC on most meters. The positive of the VOM goes to the lead from the O2 sensor. The negative from the VOM to ground. VOM (Volt Ohm Meter)
Start the car and let it idle. If the O2 sensor is working correctly then you will see the voltage on the VOM vary from a low of about 0.85 volts up to about 1.0 volt in a steady oscillation. The engine idle will probably chnage at the same rate - just a bit as the computer tries to hunt for the best mixture.
If the volts from the O2 sensor are low - about half a volt or you get nothing at all the sensor is bad. Change it out and I bet the car will pass.
When the O2 sensor is bad it will cause the car to run rich. The rich mixture will cause the cat to work over time and as a result you get a high NOX while the HC stays in line - although a little high.
Dan the Pod Guy
From inside the car disconnect the O2 sensor's big plug. With clip leads connect a VOM and set to the low voltage scale - probably 2 volts DC on most meters. The positive of the VOM goes to the lead from the O2 sensor. The negative from the VOM to ground. VOM (Volt Ohm Meter)
Start the car and let it idle. If the O2 sensor is working correctly then you will see the voltage on the VOM vary from a low of about 0.85 volts up to about 1.0 volt in a steady oscillation. The engine idle will probably chnage at the same rate - just a bit as the computer tries to hunt for the best mixture.
If the volts from the O2 sensor are low - about half a volt or you get nothing at all the sensor is bad. Change it out and I bet the car will pass.
When the O2 sensor is bad it will cause the car to run rich. The rich mixture will cause the cat to work over time and as a result you get a high NOX while the HC stays in line - although a little high.
Dan the Pod Guy
