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Emission question

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Old January 17th, 2016 | 07:54 AM
  #1  
Funkwagon455's Avatar
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From: Aledo, Texas
Emission question

I've driven my TBI 5.7liter 1992 Olds Custom Cruiser back and forth to work for over twelve years. It has 255,000 miles on the clock with Amsoil synthetic since acquisition at 50,000 miles. It runs well, cool, holds good oil pressure and has passed every state required emission test with flying colors every time. I took it in this week to get an annual inspection, ironically the last emission test that this car will be required to pass based on its age. It read high on HC,CO as well as NOx, and failed the test miserably. Based on my research and the information in my factory service manual, the HC and CO are indicative of a rich condition and the NOx is an indication of an excessively lean condition. Iv'e checked my codes and only show the standard 1-2 code, but no emission codes. How can this be? I've checked my timing,function of the egr, the cat was replaced maybe two years ago. I did replace my air cleaner as it was old and dirty. Does anyone have any experience or advise to help me effectively troubleshoot this puzzling issue?
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Old January 17th, 2016 | 08:28 AM
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Hmmm. I wonder if you have a vacuum leak somewhere. I had a vacuum leak on my Cutlass once and it caused high HC and CO due to a lean misfire in one cylinder. My car doesn't get checked for NOx so I don't have any data on how the vacuum leak would affect that.
Old January 17th, 2016 | 09:53 AM
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Of course, your 92 uses a 350 Chebby motor...

Did you follow the normal pre-test process? Complete tune up? New filters? Clean the injectors? Verify EGR function? IAC cleaning? Also, verify proper converter function. There are high-temp thermometers for checking the converter. Outlet temp should actually be about 100 deg higher than inlet temp on a properly functioning converter.
Old January 17th, 2016 | 03:29 PM
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Well, the plot thickens... I was not able to dedicate the day to this project, but did manage to pull the plugs for reference. As you can see, the #1-#4 are very clean whereas the #5-#8 are dirty and smell of gas. I will acquire a compression tester and run it through to make sure my numbers will support combustion.
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Old January 17th, 2016 | 04:08 PM
  #5  
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Originally Posted by Funkwagon455
Well, the plot thickens... I was not able to dedicate the day to this project, but did manage to pull the plugs for reference. As you can see, the #1-#4 are very clean whereas the #5-#8 are dirty and smell of gas. I will acquire a compression tester and run it through to make sure my numbers will support combustion.
Which plugs came from which cylinders. If the four plugs from one plane of the intake are all fouled, that would indicate an injector stuck open, or at least dirty. Cylinders 1-4-6-7 are on one plane and 2-3-5-6 on the other.

Old January 17th, 2016 | 07:29 PM
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As I had mentioned, 5-8 on the aft four cylinders were running cold. I managed to squeak a compression test on the aft four tonight after dinner. Thankfully all four tested above 180#. I ordered wires,cap,plugs and rotor today for install tomorrow. Once these are changed, I'll run it and use my infra red thermometer to check the catalytic converter temps.

Last edited by Funkwagon455; January 17th, 2016 at 07:36 PM.
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