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Marc
Dodge Dakota
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9/22/2004
13:10:16
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 Subject: Cause of high HC.
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Message:
Hello all. After passing my local emission rip-off...OOPS i mean test, i noticed that the limit for HC was 58ppm and my truck passed @ 48ppm. While NOT borderline, it was a weee high. I was just curious about what emission control system controls this by-product. Is it the Cat. Conv? All help appreciated.
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Hurl
Dodge Dakota
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9/22/2004
13:24:27
|  RE: Cause of high HC.
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The CAT does help eliminate HC (hydrocarbons) by after burning residual emissions.
A dead cylinder will produce HC's between 1000 to 2000 ppm (assuming the cause of the dead cylinder is not an electrically unplugged fuel injector)
Not knowing what year your truck is and how many miles are on it makes it a bit difficult to tell you what might be going on.
If your truck is older and has many miles, perhaps your cat is failing. How warmed up was your truck? Full operating temp? Did you idle for a very, very long period prior to the reading? Was the reading at idle, high idle or running at cruise on rollers?
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Marc
Dodge Dakota
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9/22/2004
13:28:17
|  RE: Cause of high HC.
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Thanks for the quick reply. The truck is a '99 and it's RARELY driven with ONLY 30,000 KMS!!!! And those are 80% highway. Anyways, it's a 3.9 and the high HC was at the 40km/h run not at the curb idle, which was CONSIDERABLY lower. The truck was up to operating temp and Eng. oil was not new, but relativley clean.
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Bob Lincoln
Dodge Dakota
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9/22/2004
14:15:35
| RE: Cause of high HC.
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I always give my vehicles a full tune-up just before emissions testing, never have a problem, not even close to the limits.
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Noltz
Dodge Dakota
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9/22/2004
16:01:27
| RE: Cause of high HC.
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All of the above notes are true. I'd like to add that 48 HC is actually quite low, and for a 5 year old vehicle that's rarely driven, it's fine. A good, long (an hour or better) run on the highway would probably bring that number down to around 20, but you'll never get into single digits... even new. The 3.9 isn't the most efficient engine, and they dont' equip them with huge cats either.
My suggestion before your next test in two years is a good boot on the highway the night before. Constant light-to-medium load for an hour or better will really get the cat lit up & burn off the excess carbon deposits that have accumulated.
I'm a licenced Drive Clean inspector & do about 12 per day.
Cheers,
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Marc
Dodge Dakota
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9/22/2004
17:50:31
| RE: Cause of high HC.
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Thanks to all you fine gentlemen that replied.
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Bob Lincoln
Dodge Dakota
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9/23/2004
08:23:03
| RE: Cause of high HC.
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In MA, they no longer test emissions at idle, instead on a dyno. My Dak yielded 0.69 grams per mile HC, limit is 2.40. That number is the same as my 4-cylinder Daytona, which always tested 2-20 ppm HC at idle when they had that test.
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