See Figures 1, 2, 3 and 4Gasoline Engines Only
The catalytic converter is a muffler like container built into the exhaust system to aid in the reduction of exhaust emissions. The catalyst element consists of individual pellets or a honeycomb monolithic substrate coated with a noble metal such as platinum, palladium, rhodium or a combination. When the exhaust gases come into contact with the catalyst, a chemical reaction occurs which will reduce the pollutants into harmless substances like water and carbon dioxide.
There are essentially two types of catalytic converters. An oxidizing type is used on many models. It requires the addition of oxygen to spur the catalyst into reducing the engine's HC and CO emissions into H 2 O and CO 2 . Because of this need for oxygen, the Air Injection System is used with all these models.
The oxidizing catalytic converter, while effectively reducing HC and CO emissions, does little, if anything in the way of reducing NOx emissions. Thus, the three way catalytic converter was developed to address this problem.
The three way converter, unlike the oxidizing type, is capable of reducing HC, CO and NOx emissions; all at the same time. In theory, it seems impossible to reduce all three pollutants in one system since the reduction of HC and CO requires the addition of oxygen, while the reduction of NOx calls for the removal of oxygen. In actuality, the three way system really can reduce all three pollutants, but only if the amount of oxygen in the exhaust system is precisely controlled. Due to this precise oxygen control requirement, the three way converter system is used only in trucks equipped with an oxygen sensor system.
The 1976-78 models utilize a floor temperature warning system, consisting of a temperature sensor installed onto the floor of the truck above the converter, a relay, located under the passenger seat, and a light, installed on the instrument panel. The lamp illuminates when floor temperatures become abnormally high, due to converter or engine malfunction. The light also comes on when the ignition switch is turned to START to check its operation. The 1979 and later models do not have the warning system.
Trucks with the catalytic converter also have a combined air control valve in 1978-1979, which control the amount of secondary air injected into the exhaust manifold. It is regulated by engine vacuum and air pump pressure, and works to keep the converter temperatures within proper limits. The combined air control valve replaces the air pump relief valve, found in the system of trucks not equipped with a catalytic converter. The 1976-77 models have an emergency air relief valve for catalyst protection. See the AIS section for a description.
All models with the three way converter have an oxygen sensor warning light on the dashboard, which illuminates at the first 30,000 mile interval, signaling the need for oxygen sensor replacement. The oxygen sensor is part of the Mixture Ratio Feedback System. The Feedback System uses the three way converter as one of its major components.
No regular maintenance is required for the catalytic converter system, except for periodic replacement of the Air Induction System filter (if so equipped). The Air Induction System is described earlier in this section. Filter replacement procedures are in General Information & Maintenance . The Air Induction System is used to supply the catalytic converter with fresh air. Oxygen present in the air is used in the oxidation process.
- Use only unleaded fuel.
- Avoid prolonged idling. The engine should not run longer than 20 min. at curb idle and no longer than 10 min. at fast idle.
- Do not disconnect any of the spark plug leads while the engine is running.
- Make engine compression checks as quickly as possible.
Testing the catalytic converter operation in the field is a difficult problem. The most reliable test is a 12 hour and 40 min. soak test (CVS) which must be done in a laboratory.
In most cases an infrared HC/CO tester is not sensitive enough to measure the higher tailpipe emissions from a failing converter. Thus, a bad converter may allow enough emissions to escape so that the truck is no longer in compliance with Federal or state stands, but will still not cause the needle on a tester to move off zero.
The chemical reactions which occur inside a catalytic converter generate a great deal of heat. Most converter problems can be traced to fuel or ignition system problems which cause unusually high emissions. As a result of the increased intensity of the chemical reactions, the converter literally burns itself up.
As long as you avoid severe overheating and the use of leaded fuels it is reasonably safe to assume that the converter is working properly. If you are in doubt, take the truck to a diagnostic center that has a tester.
If the catalytic converter becomes blocked the engine will not run. The converter has 5 year or 50,000 mile warranty; contact your local Datsun/Nissan dealer for more information.