What's the cause of a vehicle failing a smog check when the HC (PPM) is measuring to high on both 15&25mph?

Question

15mph is at 206. The max allowed is 121. 25mph is at 122. The max allowed is 101. Everything else passed fine.

Answer 1

needs a new cat :)

Answer 2

Emissions 101!
Excess HC - HC is simply unburned fuel. It is fuel that went into the engine and right back out again without being burned at all.
Excess CO - CO is fuel that went onto the engine and got lit up, but the fire went out before the fuel was fully consumed.
Excess NOx - NOx is the result of extreme heat and pressure combined. This is a natural by-product of ignition, but must be kept at a minimum.
Causes of excess HC
1) Excess heat
2) Excess fuel
3) Inadequate fuel
4) Misfire
5) Poor fuel control
6) Sleepy or flat-line Oxygen sensor
7) Vacuum Leaks
8) Defective PCV Valve
9) MAP or MAF Sensor out of spec.
10) Catalytic converter failure
11) Moisture in fuel
12) and on, and on, and on. You get the picture.
This is why the state of California wants diagnostics and repairs performed by licensed Smog Techs at licensed Smog Test Centers. There is just too much to know and understand and much too much equipment necessary for proper diagnostics. You CAN guess, and some do a pretty good job at it, but most fail miserably, and it costs lots of money repairing the part of the car that didn't really need repair.
E-Mail me ([e-mail]) with the complete test report results (ALL 5 gasses, year, make, model, engine, equipment etc) and I will try to help narrow it down a little.

Good Luck and Merry Christmas

Answer 3

Common problem are ignition system (bad spark plug wire, etc.) Always tune car and do oil change and filters before a smog.The catalytic convertor may be bad. Adding fuel injector cleaner to a low tank of gas can do it too (Personal experience).