I have a 88TC 150000 mi. I live in Ontario, Canada and am badly failing HC and CO testing. I am passing NO. I have dual exhaust and am getting approx 17mpg. There is a new catalytic converter and o2 sensor on it. Any other suggestions? This seems like high results for not bad gas milage.

Thanks Kev.

There is a charcoal filter located on the right front frame area close to the radiator. It helps to control the emissions. It probably needs to be replaced. It's called the emission cannister. And I would bet that this is your problem.