Reduced Exhaust Emissions

The 530i, 540i and 840Ci models receive a revised catalytic converter. It is slightly smaller than previously, and contains a tri-metal coating of platinum, palladium and rhodium (previously just platinum and rhodium) to improve efficiency.

All 530i models also receive a secondary electric air pump which significantly reduces hydrocarbon (HC) and carbon monoxide (CO) emissions until the catalytic converters reach operating temperature. The pump, located at the bottom of the engine compartment above the splash shield, injects air into the exhaust ports in the cylinder heads via stainless steel lines which oxidizes these combustion gases under the following conditions:

- At engine temperatures between +5°F and 11 5°F, for 117 seconds, starting 10 seconds after the engine has been started.

- At engine temperatures between -40°F and +5°F, for approximately 2.5 seconds. (prevents possible seizure due to infrequent usage).

- At engine temperatures between 115°F and 125°F for approximately 2.5 seconds.

At engine speeds greater than 3500 rpm, or at engine temperatures above 140°F, or with an engine load signal of longer than 5.5 milliseconds, the pump will not operate. It will not be activated even if the engine temperature falls below 140°F unless the engine is stopped and then started again.

The pump is energized by the DME engine control module via a relay, located in the engine compartment E-box.

If the operating conditions are met, the pump is energized, blowing filtered air upwards into a non-return valve (located directly in front of the right cylinder head) and then being distributed to the cylinder head exhaust ports via bores machined into the heads. The non-return valve is powered open by manifold vacuum supplied from a small vacuum reservoir, then controlled by an electric switching valve. The reservoir and switching valve are both mounted above the fuel supply rail on either side of the intake manifold.




Air Injection Circuit Diagram

Front

1. Engine Control Module (ECM), receives input from # 2, 3

2. Start signal

3. Engine Temperature

4. Relay, located in front power distribution box

5. Secondary Air Pump (electric), draws filtered air from # 6

6. Air Cleaner Housing

7. Non-return Valve, located in front of Cylinder # 1

8. Stainless Steel Supply Lines

9. Machined Bores at Cylinder Head Exhaust Ports

10. Engine

11. Intake Manifold

12. Vacuum Hose from Intake Manifold Rear Cover

13. Electric Switch Valve, located above Cylinder # 2

The electrical circuits for this system are described in the 1994 5 Series

Electrical Troubleshooting Manual (ETM).