BMW Coupes and Sedans 1970-1988 Repair Guide

Air Injection System

Print

OPERATION



The Air Injection system is used to add oxygen to the hot exhaust gases in the Thermal Reactor or exhaust manifold. The introduction of fresh air (oxygen) aids in more complete combustion of the air/fuel mixture lessening the hydrocarbons and the carbon monoxide emissions. A belt driven air pump is used to force air into the exhaust system, through a series of valves and tubing.

TESTING



2002 and 3.0 Models
Air Pump

See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Disassembled air pump and related parts-2002 model

Remove the air return pipe and hold the palm of the hand over the pressure regulating valve unit while increasing the engine speed. The excess pressure valve must open between 1700 and 200 rpm. If the valve opens early, replace the valve. If the valve opens at a higher rpm, replace the air pump.

BELT ADJUSTMENT

The air pump drive belt should have a deflection of no more than 0.38 inches (10mm) measured in the middle of its longest span, when properly adjusted.

CONTROL VALVE

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Control valve assembly (1) and test connection points (arrows)

The control valve should be replaced if the carburetors are difficult to adjust or if the engine back-fires when the throttle is released.

CHECK VALVE

The check valve should be replaced if air can be blown through the valve in both directions. Air should move towards the manifold only.

BLOW-IN PIPES

The exhaust manifold must be removed to expose the blow-in pipes. The pipes can be replaced by unscrewing them from the manifold and screwing in new ones.

3, 5, 6 and 7 Series Models
AIR PUMP

Disconnect the outlet hose and start the engine. The air velocity should increase as the engine speed increases. If not, the air pump drive belt could be slipping, the check valve or the air pump may be defective and would have to be adjusted or replaced.

BLOW-OFF VALVE

If backfiring occurs when releasing the accelerator or the air pump seems to be overloading, the blow-off valve may be defective.

The valve must release and blow-off during a coasting condition and the internal safety valve must open at 5 psi (34 kPa). The vacuum line must have suction when the engine is running and must allow the air to be blown off when reattached to the valve at idle.

ELECTRIC CONTROL VALVE

This control valve governs the blow-off valve and must be open at temperatures below 113°F (45°C) and closed above 113°F (45°C) of the coolant.

With the coolant temperatures above 113°F (45°C), the ignition switch on and the engine off, disconnect both vacuum hoses, attach a test hose to one nipple and blow air into the valve. The valve is functioning properly if air cannot flow through the valve. Turn the ignition switch OFF and blow into the valve again. Air should flow through the valve.

CHECK VALVE

The check valve must be replaced if air can be blown through the valve in both directions. Air should move towards the reactors only.

BLOW-IN PIPES

The air enters above the reactors, directly into the exhaust ports, behind the exhaust valves. The pipes can be replaced by removing the distribution tube assembly.

THERMAL REACTOR

The reactors have a double casing and has internally vented flame deflector plates. Spontaneous combustion, due to high temperatures, and the introduction of oxygen into the exhaust gas flow maintains the after-burning of the gases.

A warning light marked "Reactor" alerts the driver to have the unit inspected for external heat damage every 25,000 miles (40,000 km). A triggering device, located behind the dash and operated by the speedometer cable, can be reset to open the electrical contacts and extinguish the warning light.

Two different sized buttons are mounted side by side on the triggering device. The small button is for the reactor and the large button is for the EGR valve. Press the button to reset.

REMOVAL & INSTALLATION



Air Pump

See Figure 1

1600, 2002 AND 3.0 MODELS
  1. Disconnect inlet and outlet hoses.
  2.  
  3. Remove the adjusting bolt. Then, loosen and remove the front and rear mounting bolts. Note that nuts will remain in the grooved portion of the housing.
  4.  
  5. Inspect the rubber bushings inside the mounting bracket and replace if necessary.
  6.  
  7. Install in reverse order; do not pry on the pump when adjusting the belt.
  8.  

318i AND 320i MODELS
  1. Disconnect the hose at the back of the pump.
  2.  
  3. Remove the adjusting bolt and disengage the belt. Then, remove the through bolt which passes through front and rear pump brackets, being careful to retain the nut and spacer located at the rear.
  4.  
  5. Pull the rubber bushings out of either end of the air pump mount. If the bushings are worn or cracked replace them. When reinstalling, make sure inside diameters of bushings fit over the inner spacer and outside diameters fit snugly into the mount.
  6.  
  7. Install in reverse order.
  8.  

5, 6 AND 7 SERIES MODELS
  1. Loosen the adjusting bolt, which is located at the top of the upper pump bracket. Pull off the belt.
  2.  
  3. Loosen the clamp and detach the air hose at the rear.
  4.  
  5. Remove the the mounting bolts from the bracket. Remove the single bolt from the front bracket and remove the pump.
  6.  
  7. Pull the rubber bushings out of the lower pump mount and inspect them. Replace them if they are worn or cracked, making sure the inside diameters fit around the inner (metal) bushing and outside diameters fit inside the mount.
  8.  
  9. Install the pump in reverse order.
  10.  

 
label.common.footer.alt.autozoneLogo