Answer to "P0420 OBD-II Trouble Code - how to fix?"As stated, it could be a leak in your exhaust, a faulty oxygen sensor, or most likely a filthy catalytic converter. If your catalytic converter is loaded with residue and build-up, it will hamper its ability to convert raw smog into a much cleaner exhaust. Taking it off and cleaning it yourself isn’t recommended because then you will have to deal with rusty old exhaust fasteners which are a pain in the neck. If you want to give cleaning it a shot instead of replacing it altogether, try catalytic converter cleaner. There are a few effective ones in this listof the top brands.
Answer to "How do I know which engine I have? (1990 4cyl or V6?)"Engine size ie: V8-V6, or an in-line 4 or 6 cylinder, you will also need to know the displacement of the engine ie: 1.5 litre or 2.4 litre etc. This information can be found on a under hood sticker found on the firewall, on the inside of the hood or near the radiator, it can also be found in the serial number or V.I.N. found on your vehicle registration. It would also help if you knew if your engine was turbo charged or if it is a single or double overhead cam engine. Quite a few car manufacturers will label the trunk lid or front fender with some or all of this information which can be handy now that you know what your looking for. The Vehicle Identification Number or (V.I.N.), also known as the serial number is always located on the left front corner where your dashboard and front windshield meet. The left and right side of any vehicle, is always determined when you are sitting in the operators seat. You can also find your VIN number on the production plate or sticker on the door, and on some vehicles...