Miller

I recently bought a well loved 92 sc300. I tried to plate it but I can't pass emissions. the only real change done to the car is the pieced together exhaust from the PO. Looks like a wrapped ebay header, some oem exhaust pieces and two dc universal mufflers out back. I'm not throwing any codes but I can't pass emissions. Any suggestions where to start? Thanks.

ISFFUN

iTrader: (4)

I just went through this in CA. It could be anything really, so you may end up on a wild goose chase.

All the emissions components were cleaned and working on my car but it had crazy high NOx - a lot of articles / forum posts / mechanics / things will tell you that it's NOT the cats, but as an act of desperation I just replaced them with Magnaflow direct fit CA cats and my numbers went down to 80 @ 15mph and 164 @ 25mph. When I looked inside my original 97 cats, they were crumbling and in chunks.

Another note one of the first things I did was cleaned out the EGR since the little side valve was fully clogged with carbon.

KahnBB6

iTrader: (5)

^^ Some truth here. It could be many things. It also very well be one or both of your cats, Miller. If replacing them you usually want to start with the first one and before replacing the second one.

Also, your engine tune has a lot to do with the long term health of those cats and getting the numbers down when they *are* working properly. OEM cats last the longest and are the most effective but aftermarket replacement cats certified for the model and emissions type do very well for 2-3 years at a time. Catco/Airtek makes some direct fit replacements of both as custom build-to-order units.

I also agree with ISFFUN's suggestion to clean out your EGR ports. It's a bit tedious but often needed at high mileage when clogging can occur. Make sure the EGR valve, EGR tube and EGR port on the Y-manifold are clear (getting deep in there is a bit complicated). Also check your vacuum lines for a secure connection without any tears or cracks, make sure your EGR vacuum modulator and EGR VSV are working, replace both front O2 sensors with Denso units and do a full spark plug/cap/rotor/wire tuneup.

Still (as ISFFUN states above) cats in good shape make the most difference once all those things have been accounted for. Sometimes they do need to be replaced.

Aside, if your ECU has never been sent in to Tanin Auto for capacitor repair that is always a good thing to have done as a general baseline. If there are rich running or other issues that might be computer related your emissions (and the health of your cats) will be affected.

This is my extensive chronicle of a full emission system service (starting where I went into the EGR system):
https://www.clublexus.com/forums/per...-solved-9.html

And here is a recent ongoing DIY thread regarding how to fully clean the 2JZ-GE Y-manifold's EGR passage:
https://www.clublexus.com/forums/per...-cleaning.html