Passing Emissions
07-31-2004, 12:41 PM
#1
Passing Emissions
A couple of months ago I posted a thread concerning a failed emissions test for my car. It's taken me this long to respond because not a week after the test the clutch went out.
The car failed due to high NOX levels which meant high combustion chamber temperatures. CO % was 0. The guy told me the car did not have any unburned gases in the exhaust; it was runing too clean!
I considered all the suggestions I received both on this forum and on Pelican and decided to go with a suggestion from FRWilk. He said that disconecting the Hall Sensor basically retards the car's timing by 5 degrees.
I went to the inspection station, unplugged the sensor, and it passed with flying colors!
Just wanted to throw this out in case anyone with the Hall sensor cars needs this info.
The car failed due to high NOX levels which meant high combustion chamber temperatures. CO % was 0. The guy told me the car did not have any unburned gases in the exhaust; it was runing too clean!
I considered all the suggestions I received both on this forum and on Pelican and decided to go with a suggestion from FRWilk. He said that disconecting the Hall Sensor basically retards the car's timing by 5 degrees.
I went to the inspection station, unplugged the sensor, and it passed with flying colors!
Just wanted to throw this out in case anyone with the Hall sensor cars needs this info.
07-31-2004, 10:54 PM
#4
Three Wheelin'
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Thanks for posting the results. FRWilk knows the 944s, doesn't he.
And I'm glad you got it through. But if you re-install the Hall sensor, the car will still be running lean. That's not good. Hopefully, you can find the problem and fix it. Good Luck.
And I'm glad you got it through. But if you re-install the Hall sensor, the car will still be running lean. That's not good. Hopefully, you can find the problem and fix it. Good Luck.
08-01-2004, 03:17 PM
#6
Drifting
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Mine JUST didn't pass last week with high NOX level. SO, I went over and pulled my spark plugs to take a look, they have a yellow/brown color! Plus they are only 10 months old, Beru ones. So then I thought, with Guru 15psi chip set, new Tial 38mm wastegate, I am really close to pushing 50 extra hp. I have heard that about 75hp increase one should change the plug with a colder one, so that is what I did and now I am just waiting until tomorrow to go test it.
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08-02-2004, 01:05 PM
#8
Burning Brakes
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If it failed nox only It is probably the converter. Mine passes even with a chip in it. Pulling the hall sensor backs off the timing thus cooling the combustion temps which reduces nox.
08-02-2004, 10:18 PM
#11
Three Wheelin'
For Jscottie:
Shoot your mechanic. When an O2 sensor fails the DME defaults to a rich mixture to prevent the engine from running lean. A "normal" mixture will give an O2 sensor output of about 0.50 volts DC. A higher output is rich, a lower output is lean. If you disconnet the O2 sensor with the engine running and use a digital volt meter to read the DME side of the sensor connector, you should read 0.45 volts. So, with a bad or disconnected sensor, the DME "thinks" the mixture is lean, and to compensate the DME legnthens the injector duty cycle to richen the mixture.
I would start looking for vacuum/intake leaks. Check your plugs. Lean running plugs will be bright yellow to white. Leaking injector seals will cause the affected cylinder to run lean.
Shoot your mechanic. When an O2 sensor fails the DME defaults to a rich mixture to prevent the engine from running lean. A "normal" mixture will give an O2 sensor output of about 0.50 volts DC. A higher output is rich, a lower output is lean. If you disconnet the O2 sensor with the engine running and use a digital volt meter to read the DME side of the sensor connector, you should read 0.45 volts. So, with a bad or disconnected sensor, the DME "thinks" the mixture is lean, and to compensate the DME legnthens the injector duty cycle to richen the mixture.
I would start looking for vacuum/intake leaks. Check your plugs. Lean running plugs will be bright yellow to white. Leaking injector seals will cause the affected cylinder to run lean.
08-03-2004, 10:36 AM
#12
8th Gear
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Funny to read this thread...I too just went through this ordeal and figured I would share. I had a 3" high-flow cat installed several years ago and thought it would still be good. I went to MD emissions for the test and failed miserably. The car ran excellent, plugs were perfect everything mechanically is in top shape. My NOx were high though and my fuel trim was a bit rich. I took out the chip and replaced it with the stock one and ran it again but I took it to VA instead to get readings. I'd rather pay VA the $20 for two tries vs. MD's higher rate. The fuel trim leveled out but my NOx was still high. I was convinced that I had a bad cat or a hollowed out cat more like it.
I went to my exhaust shop and asked them to rip out the high-flow and inspect it. They took it off and it was hollowed out. Luckily I saved my stock one which was iin great shape and replaced it. Placed the AutoThority chip back in it and crossed my fingers. Took it back to MVA and got the car to pass with Honda like ULEV colors. The operator was impressed at how clean this Porsche had passed.
If you have a high NOx count (as mentioned earlier) inspect/suspect the plugs, fuel psi regulators, O2 sensor and possibly a bad cat. A weak coil can also lend to not providing a full combustion.
Here are my readings from MVA-
Hydrocarbons-
state allowed-1.8000 GPM
inspection read- 0.1472 GPM
Carbon Monoxide-
state allowed- 30.0000 GPM
inspection read- 0.8582 GPM
NOx-
state allowed- 2.8000 GPM
inspection read- 0.0982 GPM
I'm not going to mess with the high-flwo cat again, it did provide more power but it is a hassle to replace and remove.
I went to my exhaust shop and asked them to rip out the high-flow and inspect it. They took it off and it was hollowed out. Luckily I saved my stock one which was iin great shape and replaced it. Placed the AutoThority chip back in it and crossed my fingers. Took it back to MVA and got the car to pass with Honda like ULEV colors. The operator was impressed at how clean this Porsche had passed.
If you have a high NOx count (as mentioned earlier) inspect/suspect the plugs, fuel psi regulators, O2 sensor and possibly a bad cat. A weak coil can also lend to not providing a full combustion.
Here are my readings from MVA-
Hydrocarbons-
state allowed-1.8000 GPM
inspection read- 0.1472 GPM
Carbon Monoxide-
state allowed- 30.0000 GPM
inspection read- 0.8582 GPM
NOx-
state allowed- 2.8000 GPM
inspection read- 0.0982 GPM
I'm not going to mess with the high-flwo cat again, it did provide more power but it is a hassle to replace and remove.
08-03-2004, 02:21 PM
#13
Drifting
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I am going to just get collor plates for my car soon so I don't EVER have to worry about emissions with the Porsche again. After that, a test pipe is going in. Like to see the performace difference.