90 Merc Wagon failed emission test


Old 12-05-05, 09:57 AM
Thread Starter
Join Date: Apr 2002
Location: USA
Posts: 110
90 Merc Wagon failed emission test

2 years ago, you were most helpful in assisting with the diagnosis of a bad EGR valve.

Well, I think the problem this time is something else as the NO readings were OK.

Here are the results from Jan 8, 2004 as well as Dec 2, 2005:

Jan 2004

HC ppm-----101-----60-------Pass-----98------68------Pass
NO ppm----0757----197--------Pass---0690-----250------Pass

Dec 2005

HC ppm-----0055----69-------Fail-----0060-----189------Fail
NO ppm----0720----104--------Pass----700------82------Pass

The values on the left are @15MPH, while the values on the right are @25MPH.

The car is a 1990 Merc Colony Park Wagon (5.0L V8, AT) with 175K miles
No major work done in the past 2 years, but used only once per week on average for short trips (one commute of 30 miles RT, plus hauling building materials from HD/Lowes).

Oil changed every 3K miles or twice per year. Due for next one by 1/1/06.

Replaced air filter while in line for inspection.

Any suggestions, please?


Update on 12/19:

I found a fouled plug and replaced it, and ran some Chevron fuel system cleaner through. Also ran a can of TB cleaner through, plus replaced the PCV breather filter thing. Took it back for a reinspection. Failed again, but getting better:

The HCs were down to 68 and 72, respectively. Everything else passed fine.

Any suggestions, please? How can I get the HCs down further?

Last edited by sleepy hollow; 12-19-05 at 03:37 PM.
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Old 12-19-05, 03:38 PM
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Join Date: Apr 2002
Location: USA
Posts: 110
See update to message above. I would appreciate suggestions. Thanks.

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