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Failed Smog Test

1989 Lincoln Town Car Failed Smog Test

Smog test was done and visual and functional tests had passed. But the emission test failed on my 1989 Lincoln Town Car failed at 15mph. It should be max 524 but it measured 863. At 25mph it should be 481 and measured 605. I had the catalytic converters checked and they are clean. I'm currently installing a new egr valve. What else can I look for to correct the emissions so I can pass the smog test? The car runs good, no smoke out the back and car has good power. Any suggestions?


Your Lincoln Town Car's EGR valve is a great start, in fact it might be all it needs to pass the smog check. NO is created when engine combustion temperature rise above 2500f. The EGR valve introduces inert gas to the intake manifold and dilutes the air/fuel mixture so the engine runs cooler. If the new EGR valve doesn't fix the problem you want to make sure the valve is getting manifold vacuum and opening properly.

Next check fuel mixture. Any condition which would cause a lean fuel mixture will cause high NO as well. Things to look into would be defective/damaged oxygen sensor/s, clogged fuel injector/s, high compression, defective MAP sensor.

A good indicator of a lean fuel mixture is low CO.

posted by SmogTips Support 04-03-2013 07:37 PM
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