beautiful!! yes thats single point injection. usually its not a bad sensor that causes this, its the cat converter that has that much soot deposits that as exhaust gas flows through it, it never contacts the catalyst to convert the carbon monoxide into carbon dioxide. so one thing you can do to rejuvenate the cat converter is while the engine is running at a fast speed inject a fine mist of water into the engine air intake. not too much but just on the verge of causing the engine to bog down. the water hitting the cat effectively steam cleans it taking all of the built up soot deposits away from the catalyst. just be sure to put something under the exhaust at the back of the car to catch the water as it will be very black and stain whatever surface it falls on. you only have to do it for about 5 mins and thats it.
its what i had to do to get my 903cc with electronic carb through the MOT. after that it never had the issue again. i have done it on other cars with great successes too. worth trying
the alternative is replacing the cat converter which is totally unnecessary as it can be cleaned as above.
if you have the engine management light on (the red injector light) that could be the lambda o2 sensor on the exhaust faulty. if not it is still fine.
i would have though that on yours being a 1991 it would only be a single wire o2 sensor? at max a 3 wire.
the wire colours are as follows:
Black wire is the sensor reading wire.
the 2x white wires are for the built in heater (usually the part that fails however it will still work once it has been running for a while)
Grey wire is just an earth wire.
you can run a 3 or 4 wire sensor on a 1 wire ecu. you just use the single black wire and leave the other wire disconnected.
on vehicles without a turbo, the lambda (o2) sensor is narrow band and quite cheap.
however for vehicles with a turbo, they use a wide band sensor.. which can be quite expensive.
hope this helps!
