A. A 1993 Accord failed smog somewhere else for HC (unburn fuel). She spent over $1000: replaced catalytic converter, replaced spark plugs and rotor, new oxygen sensor, and fuel system clean but still failed smog for HC :( We did a $120 diagnostic and found the EGR system clogged. Normally, an EGR clog would be high NOx but this car is different. Not all ports from the EGR valve is clogged leading to misfire at cylinder(s) because too much exhaust is channeled toward cylinder(s) that are ok. We performed a thorough EGR valve clean and HC were brought down to almost 0 ppm. Total bill was $300.
B. A 1998 Chevrolet Silverado failed smog for air injection pump code. Prior to seeing us, the air injection pump lines were cleaned and a tune-up was performed. He spent over $1000 (same story different day) but still failed smog for the same reasons. A quote for a catalytic converter and oxygen sensors were the next components to be replaced but he decided to called us for a second opinion. We charge $120 for diagnostic and found the air pump internal filter fell apart and jammed the impellers. We also charged $240 to un-jammed the intake and rebuild the air pump. A new air pump is about $500. Emission repair is very precise. It's very tempting to throw parts at the problem.
C. A 1995 Ford Ranger comes in for NOx failed on multiple occasions. The egr (exhaust gas recirculation valve) ports were cleaned & egr valve replaced but NOx unchanged. He spent over $1000 (here we go again--i am noticing a pattern) and a catalytic converter and an oxygen sensor were next to be replaced. He was told @ 170k miles the catalytic converter and o2s supposed to be replaced. We charged $120 for diagnostic and found: 1. There was no vacuum to the egr valve and 2. The combustion chamber area was full of carbon deposit. We fixed the vacuum issue and did a fuel induction clean. The total out the door was $379. Smog check passed--clean.
When it comes to emission repair, or any auto repair in general, it's very precise and it follows a proper diagnostic. Guessing & throwing part at the problem is a waste of money.
D. A 1998 Toyota 4Runner with 169,000 miles failed for NOx. Customer been to different shops and still failed. The vehicle has numerous new parts including a new catalytic converter. We did a diagnostic and found extensive carbon deposits and bad front oxygen sensor (AFS). This vehicle is not equipped with EGR valve to fight NOx. We charge $120 for diagnostic, $120 for de-carbonizing, and $60 labor for replacing the oxygen sensor. Yike! I don't know how much she has paid before :(