Smog question high HC (ppm)
Thread Starter
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
Smog question high HC (ppm)
My 305 GMC pick up with 155,00 just barely passed a smog with a reading of 95 HC (ppm) That's the max allowed. The NO is high too. 789 at 15 mph and 232 at 25 mph. Can someone tell me what's wrong? It runs perfect.
Last edited by Kool88vette; Jul 24, 2009 at 07:33 PM.
Safety Car
Joined: Jan 2004
Posts: 3,783
Likes: 15
From: Northern California
High NOX levels are the result of high combustion temperatures.
Is the EGR valve working correctly and do you have a free flowing exhaust which reduces the backpressure needed for the EGR valve to operate?
Did you do a complete tune up before the emission test too include an oil change, spark plugs, cap, rotor, O2 sensor, air filter and timing?
All of the above will contribute to high HC levels.
Is the EGR valve working correctly and do you have a free flowing exhaust which reduces the backpressure needed for the EGR valve to operate?
Did you do a complete tune up before the emission test too include an oil change, spark plugs, cap, rotor, O2 sensor, air filter and timing?
All of the above will contribute to high HC levels.
