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2003 BMW M3 Can't pass smog check in California

Tiny
LEXESTY
  • MEMBER
  • 2003 BMW M3
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 82,000 MILES
Hello,

My BMW M3 has high HC (hydrocarbons) at
15mph measured 98 and the Max is 51,
25mph measured 77 and the Max is 35. I have done the tune-ups and oil change. The CO% and NO(ppm) passed without any problems. How can I bring down the HC reading? Does that mean my cats are bad?

Thank You!
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Sunday, November 22nd, 2009 AT 1:44 AM

3 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
My BMW M3 has high HC (hydrocarbons)

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.
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Sunday, November 22nd, 2009 AT 2:28 AM
Tiny
LEXESTY
  • MEMBER
  • 2 POSTS
So, my cats should be in a working condition, correct? Will the HC be reduced if the old cats are replaced?

Thanks Again!
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Sunday, November 22nd, 2009 AT 3:18 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Will the HC be reduced if the old cats are replaced?

That's the Cat's job is to lower the HC/CO
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Sunday, November 22nd, 2009 AT 4:25 AM

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