Van failed emissions twice


Old 05-20-13, 06:03 PM
Thread Starter
Join Date: May 2013
Posts: 3
Van failed emissions twice

Just bought this van, 1995 GMC Vandura 2500 5.7L. The guy I bought from didn't have to do emissions. Failed 1st time I changed air filter, plugs, wires, cap, rotor. All of which were in need of changing. I'm actually amazed it ran. Wife took it back in & it failed worse than the first time. That was a huge shocker. What caused it to fail worse? It failed with the HC & NOx both times. CO passed both times but got worse like everything else. HC went from 2.0270 to 2.3228, NOx went from 4.5541 to 4.9837, CO went from 14.4306 to 18.5541. I live in Denver, CO, so that tells you my environment. The two tests were only 3 days apart. Except for the air filter I thought I was upgrading the other components. Nothing crazy, just next level. I plan on doing light towing with it. Any help greatly appreciated. I'm at a loss.
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Old 05-21-13, 03:22 AM
Join Date: Feb 2013
Location: United States
Posts: 197

Do a scan for error codes, and post any codes you find.

Hydrocarbon failures mean unburned gasoline is passing through the engine and entering the exhaust. The three most common causes include ignition misfire, lean misfire and low compression (typically a burned exhaust valve). Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires or a weak coil. Lean misfire results where there is too much air and not enough fuel, so check for vacuum leaks, dirty injectors or a fuel delivery problem. In addition to these, hydrocarbon failures can also be caused by oil burning due to worn valve guides, valve guide seals and/or rings. Carbon monoxide failures indicate an overly rich fuel mixture. The system may not be going into closed loop because of a bad coolant or oxygen sensor. When both HC and CO are high, the vehicle may have a bad catalytic converter or an air pump problem. NOX failures are usually EGR-related, since the EGR system is primarily responsible for reducing oxides of nitrogen. But NOX emissions can also be caused by a bad three-way converter or a computer control system that remains in open loop.

Thank You

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