Failed smog 3 times. I had about 5 leaks in the piping that I just got welded. They were in the form of unwelded pipes creating gaps from the y-pipe to the cats and the intermediate pipe. Would these leaks have affected the smog check readings?

 

my left cat has a leak in it and i passed... in my case no i guess

 

You should have received a slip showing where you failed smog. It should not be a mystery to you.

 

I will presume you didn't understand my question and are unable to use tact.

The fact that the slip shows I failed HCs at 25mph indeed is not a mystery, if that is what you meant. My question was WHY.

Anywho, I spoke to the technician and he said that if the leak is before the O2 sensors then that would have caused the oxygen readings to be inaccurate thus causing the car to fail the test.

OUT.

 

If you have an air leak before the O2 sensors, it causes a "false lean", the PCM adds fuel the engine doens't need, it runs rich and you see excessive HC and CO.

 

OK, now you have revealed WHY you failed smog. Mystery solved! It's always helpful to include such pertinent information when you ask for advice. Tact has nothing to do with it. But if your feelings are hurt . . .

 

Actually, the WHY I was referring to was, "Why did I fail HCs?" In other words, "What was the cause?" Hence, the inquiry about the exhaust leaks. Alas, the technician did answer my question.

Telling someone that it shouldn't be a mystery sounds a tad sarcastic. Consider rewording your point so it would actually be helpful.

Thank you Injuneer for your post. Problem confirmed.