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I went to my smog guy this morning to get my 92 SC400 smog tested. Prior to today, I have changed both upstream O2 sensors and the sub catalytic converter. He did a pre-test by putting the car on a roller and stuck a probe in the tailpipe to take readings while the car is running at around 16mph.
The result:
HC (ppm) - 150
CO% - 0.06
CO2 % - 14.50
NO (ppm) - 139
The smog tech told me to check the EGR valve and make sure it isn't clogged. He also said that it's also a good idea to change the spark plugs too. I just checked the plugs 2 weeks ago and they still look good. The plug wires look very old though so I'm going to get a new set of wires, ignition distributors, and rotors. Anyhow, the tech pointed out the EGR valve which is the one next to the intake manifold in the picture below. My other car is a Z32 and the EGR valve is in the back of the engine right above the transmission and is nearly impossible to get to w/o an engine pull. Before I get my hopes up, I just wanted to confirm with you guys if the EGR location is correct as shown in the photo below. I also read a how-to for the LS400 but it has an EGR vaccum modulator filter that can be checked and cleaned. I don't see this on my SC400, perhaps these cars don't have it, correct me if I'm wrong. Any other suggestions on what to check? I'm also going to run Seafoam through the system before I return to the smog station.
I own a 300 but I believe that is the idle air control motor. you're looking for a valve that has 2 vacuum lines and 1 line going into the intake where its bolted too. it comes off the exhaust manifold.
mikef, the car runs great! No abnormal noise. Engine idle is smooth, no missing. It used to run rich and I could smell it from the tail pipes before replacing the front O2 sensors, now it's gone. It's just the high NO that is causing it to fail.
Will fail smog test!
