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1981 Toyota Pickup Failed Smog Check For High HC and CO

Hello. I own a 1981 Toyota Pick-Up Truck. It's a 4 cylinder with a manual transmission. I just went to get my truck smogged and it came back as failing on the ASM emission test result.

It failed at 15 MPH of the smog test: HC at 287 and CO at 2.19. It passed on the 25 MPH. Can you give me an idea of what it could be before I take it to a shop for repairs so I know what to expect. Thank you.

Answer:

We're going to have to recommend a smog check repair station first find out if and why your Toyota Pick-up truck is producing high CO, if in fact it is producing high CO (rich fuel condition) and the high CO is not the result of incomplete combustion due to the high HC. CO stands for Carbon Monoxide. It is a by-product of incomplete combustion, more then often related to the presentation of too much fuel to the combustion chambers. The spark created at the spark plug can only burn a small amount of fuel, the fuel it cannot burn is sent out the tailpipe and will normally contain high levels of partially burned fuel(CO) and un-burned fuel(HC). The diagnosis for this fault should begin with inspection of the carburetor “feedback” system. This includes ensuring the oxygen sensor is working properly, your vehicle's emissions computer is receiving the signals from the oxygen sensor, the computer is computing the data properly and sending the correct signals to the carburetor to either increase or decrease fuel delivery to the combustion chambers. Fuel distribution on your Toyota Pickup Truck is controlled by the carburetor. If any component within the carburetor is defective air/fuel ratio can be disrupted and result in incomplete combustion. The presentation of too much fuel will produce high CO emissions. The presentation of not enough fuel will produce low CO emissions. If your engine's carburetor is defective you have two options. You can ask a smog repair station to try and adjust it or you can ask to have the carburetor rebuilt. posted by SmogTips Support

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