I am going to assume this is similar to the 86,87,88 USA model samurai. these use a feedback carb., the o2 sensor in the exhaust send a rich-lean signal to the ecm which control a mixture soleniod in carb. the o2 signal is voltage. When the exhaust is lean the voltage drops to less than 0.4 volts and when rich is greater than 0.4 volts with a max reading of around 1 volt for a very rich signal.
the o2 sensor is best checked with a lab scope but you can use a volt meter. with everything connected you need to back probe the o2 connector (USA model use one wire o2 sensor) to get the voltage signal betweem the o2 and ecm. with engine warmed up you should varying voltage signal above and below 0.4 volts. if you disconnect a vacuum line you should see the voltage bias to the less than 0.4 readings and if you choke the carb the voltage should bias to greater than 0.4 volts.
a shorted o2 sensor will give a 0 volt signal falsely telling the ecm the exhaust is lean, the ecm will then send a signal to carb to add fuel and richen mixture. the engine may not run badly right away but the fuel milage will drop.
this is a good place to start and of course you need to check the basics like plugs , wires , timing , loose vacuum line , ect . let me know what you find and if this doesn't fix problem, I will help you check the rest of the system.
SQUID
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