Q: Over the last several months I have acquired numerous questions regarding smog systems, including how smog systems work, vehicle application, interpreting date codes, rebuilding your own system, how to de-vein your GM smog pump, and how diagnose problems with or how to delete your C4 smog pump. We will try and answer all of these questions in this one article.
A: Collectively, our personal vehicles account for nearly one-fifth of all U.S. emissions. This is a major cause of global warming, emitting around 24 pounds of carbon dioxide and other global-warming gases for every gallon of gas.
The Motor Vehicle Air Pollution Control Act of 1965 was an amendment to the U.S. Clean Air Act of 1963. The amendment set the first federal vehicle emissions standards to begin with the 1968 vehicle model year. The new standards set forth a substantial reduction in emissions from those found in the Clean Air Act of 1963.
This amendment was established to reduce hydrocarbons (HC)—a class of burned or partially burned fuel—by 72 percent, carbon monoxide (CO)—a product of incomplete combustion—by 56 percent, and crankcase hydrocarbons by 100 percent.
The first automotive emission pollutant to be reduced was crankcase hydrocarbons. This was accomplished by creating a Positive Crankcase Ventilation (PCV) system. The PCV system draws crankcase fumes containing unburned hydrocarbons into the engine’s intake so they can be burned rather than releasing these unburned vapors from the crankcase into the atmosphere. PCV systems were first installed on a widespread basis in the 1961 model year, and by 1964 most new cars sold in the U.S. were equipped with a PCV system. PCV became standard on all Chevrolets in 1968 and is still used today on all cars
Air Injection System & Smog Pump
The early Air Injection System (AIS) or Smog Pump systems were designed to introduce clean air to the engine exhaust soon after it exits the exhaust manifold. Exhaust gases are at their hottest as they leave the combustion chambers, so introducing oxygen into the exhaust at this point allows unburned hydrocarbons to continue to be burned as they travel down into the exhaust system and ultimately out the tailpipe.
Air Injection Systems consist of mainly two different designs, a Pump Type and a Pulse Type. If a vehicle did not have an air pump installed on it the Controlled Combustion System (CCS) may have been used.
Pump Type: The Air Pump, or Air Injector Reactor (AIR), system design is commonly referred to as the smog pump. The smog pump is responsible for supplying fresh, pressurized oxygen into the exhaust stream near the exhaust manifold. The spinning vanes of the air pump forcing air into the diverter valve accomplish this. During acceleration, air will be forced through the diverter valve, the check valve, the air injection manifold, and into the exhaust stream where it is mixed with exhaust gases to help burn off any unused hydrocarbons.
During deceleration the diverter valve blocks airflow, preventing a backfire that could damage the exhaust system. When needed, the diverter valve will release excess pressure into the air cleaner.
The components of this system are the air pump, the diverter valve, the air distribution manifold, air check valve, and exhaust manifold equipped for air injection.
Pulse Type: The pulse type system uses vacuum to draw fresh oxygen into the air injection system. This vacuum is created by the exhaust gases as they travel down the exhaust passages at a high rate of speed. This fresh air then travels through the diverter valve, check valve, and to the exhaust manifold where it’s mixed with exhaust gases to help burn off any unused hydrocarbons.
Controlled Combustion System: This system was introduced in 1968 and was used on vehicles that did not receive the pump type or pulse type AIR system. The CCS concept was to improve combustion efficiency by recalibrating the carburetor and distributor settings as well as using a higher engine operating temperature.
The higher engine operating temperature was accomplished by installing a 195-degree (F) coolant thermostat instead of the 180-degree (F) thermostat that had been used in the past. Also, the use of a thermostatically controlled air cleaner system was designed to help warm the intake air temperature to 100 degrees (F). This system consisted of a damper door mounted on the snorkel of the air cleaner that directed warm air from a heat stove on the exhaust manifold into the air cleaner.
The CCS system was a less performance-oriented emission control system than the pump or pulse type systems. That is the reason Corvette chose not to use the CCS system on its performance-based engine packages.
Corvette Air Injector Reactor System Application
1. Air Injection Reactor systems were first used on Corvettes in 1966 California-delivered models, except for the L72.
2. For 1967 Corvettes, AIS was a mandatory option on all Corvettes delivered to California.
3. For the 1968 and 1969 model year all Corvettes had the AIR system installed, regardless of engine or transmission package for all 50 states.
4. For 1970, Chevrolet went to the Controlled Combustion System (CCS) for emissions control on most Corvettes, except for the LT-1, which retained the AIS system.
5. For 1971, most Corvettes continued to use CCS except LT-1 and LS6, which used the AIR system.
6. 1972 saw a return to the AIR system for most engines, except for the L48 coded “CKW” and “CKX.”
7. For 1973 through 1975 Corvettes, all engines used the AIR system.
8. For 1976, most Corvette engines returned to CCS except California-certified cars, which retained the AIR system.
9. In 1977, all Corvettes used CCS except California and “High Altitude” delivered cars, which used the AIR system.
10. For 1978 and 1979, all High Altitude and California cars and those equipped with the L82 engine used the AIR system. All other Corvettes used the CCS. Remember, the L82 engine was not available in California or “high altitude” areas during these years.
11. For 1980 through 1987, all Corvettes used the AIR system. The AIR system was used on most Corvettes through the 1996 model year.
12. Some C4s Corvettes used an AIR system that incorporated an electric air pump.
The first smog pumps introduced in 1967 were a serviceable three-vane pump design with the pulley attached to the pump using four bolts. This pump was redesigned in 1968 with a “non-serviceable” two-vane pump design with the pulley attached to the pump using three bolts. This design was used through the mid 1970s. Later in this article we will go through the rebuilding process for all AIR pumps.
Corvette Air Injection Pump Date Codes
1. The first three characters, 119, refer to the day of that year, this number is also known as the Julian Calendar Date. The Julian Calendar Date is the 365-day calendar with a continuous count of days in the year. So in 1970, 119 would equal April 29.
2. The fourth character, 0, equals the year. In this case, 1970.
3. The fifth character, 1, is the plant shift code. The 1967 AIR pumps were coded 1 or 2, and most 1968 and later pumps were coded 1. 1 equals first shift and 2 equals second shift.
4. The last character, S, is the configuration code of the pump. All 1967 Corvette AIR pumps are coded P. The 1968 AIR pumps with a pressure relief valve installed in the pump are coded Y. The 1968 AIR non-pressure relief valve pumps were coded Z. Most 1969 and later pumps without a pressure relief valve are coded S.
Corvette Air Injection Smog Pump Fans
A white smog pump fan was used on smog pumps from 1968 to mid-year production 1972. Pumps and service parts manufactured after that date used a black fan.
The pulley part number used on the air pump varies depending on application. The Assembly Instruction Manual (AIM) can be helpful in finding the correct part number for your application.
Diverter Valve / Fuel Mixture Control Valve
To prevent backfiring under deceleration conditions, the 1966-’67 Corvette AIR system used a fuel mixture control valve that supplied the intake with extra air during decel conditions to help lean out the air/fuel mixture. This method was inadequate and in 1968 the system was redesigned to reduce backfiring.
In 1968, the introduction of a diverter valve fixed this problem. The diverter valve momentarily stops air from being injected into the exhaust ports, preventing backfire from the ignition of the unburned fuel in the exhaust gases.
Diverter valves may look similar on the outside but the internal calibration can be different. The different calibration can cause a backfiring condition on deceleration if used in the wrong application. The Assembly Instruction Manual (AIM) can be helpful in finding the correct part number for your application.
The last five digits of the diverter valve part number are stamped on the diverter valve mounting flange. The mufflers were plated with gray phosphate. The broadcast code is ink-stamped on the diverter valve until 1970 and then a label was used.
Check Valves / Air Manifolds
In 1967, the smog pump was connected to the backfire check valves, which was connected to the fuel mixture control valve.
For vehicles built after 1968, the output of the smog pump went through the diverter valve first, then to a backfire valve mounted on the air manifold. The check valves are gold cadmium plated.
Air Injection Tubes
This month we have identified all the components of the AIR system and how to read the codes. Next month be ready to roll up your sleeves and get dirty. We are going to be rebuilding an AIR pump and de-vein your GM smog pump. We will also go over all the things that will need to be done along with the smog pump de-vein. Don’t worry C4 guys I will not forget you.