1988 Lincoln Town Car Failed emission test

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Engine problem
1988 Lincoln Town Car V8 Two Wheel Drive Automatic 117971 miles

This year: 25/25 Test 50/15 Test
Reading Allowed Reading Allowed
HC ppm 289 124 277 128
CO % 5.38 0.79 3.83 0.72
NO ppm 71 859 66 939
RPM 1137 2500 max 1429 2500 max
CO+CO2 % 16.8 6.0 min 16.2 min
Everything passed last yea with flying colors. Catalytic converter replaced last year. Ca coughs (or backfires) occasionally, not sure which but otherwise runs fine.
Money is short as with most I guess. Trying to understand what the problem might be and what I might be looking toward in the cost realm. Much Thanks in advance.

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Tuesday, February 12th, 2008 AT 11:47 AM

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  • 77,150 POSTS

HC ppm 289 124 277 128
CO % 5.38 0.79 3.83 0.72 This one don't look too! Good. Could be a catalytic converter or an air injection problem-its not scrubbing it-might want to check the 02 sensors switching activity-

Below is something to look at:

Engine and/or converter not at operating temperature. If a vehicle is only driven a short distance to the test facility, it may not be warm enough for the engine to be at normal operating temperature and/or the converter at light-off temperature. This will affect the emissions of the engine and may cause it to fail.

Excessive idling while waiting in a test lane may also cause the catalytic converter and/or oxygen sensor to cool down enough where they may not control emissions properly causing higher than normal readings.

Idle speed too high. A few hundred rpm can sometimes make the difference between passing and failing an emissions test if emissions are marginal.

Dirty air filter. A restricted air filter will choke off the engines air supply, causing higher than normal CO readings.

Worn or dirty spark plugs. Excessive plug gap and fouling deposits can create ignition misfire resulting in excessive HC emissions.

Dirty oil. The oil in the crankcase can become badly contaminated with gasoline if a vehicle has been subject to a lot of short trip driving, especially during cold weather. These vapors can siphon back through the PCV system and cause elevated CO readings.

Pattern failures. Some vehicles tend to be dirtier than others for a given model year because that is the way they were built. It may be the design of the engine, or the calibration of the fuel or engine control system. These kinds of problems may require special "fixes" that can only be found in factory technical service bulletins

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Tuesday, February 12th, 2008 AT 12:13 PM

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