Secondary Air Injection (SAI)

24-6 Fuel Injection

Secondary Air Injection (SAI)

The secondary air injection (SAI) system uses an electric pump to inject ambient air into the exhaust stream after a cold engine start. This strategy effectively reduces the warm up time of the catalytic converter, resulting in a reduction of HC and CO emissions. The DME engine control module (ECM) controls and monitors the secondary air injection system.

NOTE–

• 993 cars sold in the US were fi tted with secondary air injection (SAI).

• On 1996 and later cars (DME M 5.2), the SAI system is monitored by OBD II software. On DME M 5.2 cars, insuffi cient SAI air fl ow faults can turn on the Check Engine light.

• 1995 cars are OBD I compliant which does not monitor the SAI system.

The SAI pump is mounted to the right rear of engine behind intake manifold.

1. SAI pump air intake hose

2. SAI pump

3. SAI pump vacuum solenoid

4. SAI pump electrical connector

5. SAI pump control valve vacuum hose

6. Air pipe to left camshaft housing

7. SAI control valve

8. Air pipe to right camshaft housing

9. SAI check valve

When the SAI relay is energized by the DME control unit, power is supplied to the SAI pump and the vacuum switching solenoid. When the switching solenoid is energized, engine vacuum opens the control valve to allow SAI pump air to be injected through the SAI check valve and into the left and right camshaft housings.

From the port in the camshaft housings (A), air fl ows through the bores in the camshaft housings (arrows) into the exhaust ports in the cylinder heads.

Air fl ow from camshaft housing is directed into transverse passage (A) in cylinder head in exhaust port.

Fuel Injection 24-7Secondary Air Injection (SAI)

24

Common SAI issues

Owing to the harsh operating environment, it is not uncommon for the SAI air passages and check valve to become clogged with combustion by-products (unburned exhaust gases, oil residue). This clogging results in insuffi cient fl ow or no fl ow of secondary air into exhaust system.

DME M 5.2 OBD II SAI fault codes:

• P0410 - Secondary air injection, insuffi cient fl ow (cyl. 1-3)

• P1411 - Secondary air injection, insuffi cient fl ow (cyl. 4-6)

OBD II SAI monitor: When the SAI pump is commanded by the DME control unit to run (only during cold start conditions), the oxygen sensor senses the excess oxygen condition. If the SAI ports are blocked, additional air will not be detected in exhaust, and an insuffi cient fl ow fault will be set in the DME control unit.

If the blockage is simply at the one-way check valve, the valve can be replaced fi rst to see if air fl ow is restored. But if the check valve is severely blocked, the passages in the camshaft housing and cylinder heads may also blocked. Properly cleaning blocked passages requires engine disassembly to access the ports in the camshaft housings and cylinder heads.

Secondary air injection components

1. Air pipe to left side camshaft housing

2. Air pipe to right side camshaft housing

3. Hose

4. SAI control valve (shut-off valve)

5. SAI check valve

6. Air distributor housing

7. Hose

8. SAI vacuum solenoid

9. Connector

10. SAI pump

11. SAI air intake hose

established 1950Automotive Reference™

Bentley Publishers, 1734 Massachusetts Avenue, Cambridge, MA 02138-1804 USATel: 617-547-4170 • Toll Free: 800-423-4595 • Fax: 617-876-9235http://www.bentleypublishers.com/contact-us

Porsche 911 (Type 993) Service Manual: 1995-1998Carrera, Carrera S. Carrera 4, Carrera 4S

Bentley Stock No: P998Publication Date: 2013-11-04ISBN: 978-0-8376-1719-0Hardcover, 8 3/8 in. x 11in.Case quantity: 1946 pages 1,523 full color photos and illustrations

The Porsche 911 Carrera (Type 993) Service Manual: 1995-1998 is a comprehensive source of service information and specifications for Porsche 911 (Type 993) Coupe, Cabriolet and Targa models from 1995 to 1998. The aim throughout this manual has been simplicity and clarity, with practical explanations, step-by-step procedures and useful specifications. Whether you’re a professional technician or a do-it-yourself Porsche owner, this manual will help you understand, care for and repair your Porsche.

Technical highlights

• Full-color repair manual pages (black and white electrical section).• In-depth maintenance instructions for everything from changing the

engine oil (and both oil filters) and Tiptronic transmission fluid to replacing the cabin microfilter. This manual tells you how and when to do it.

• Type 993 enthusiast guide with year-to-year model specifics, and a comprehensive listing of Porsche option codes.

• Step-by-step engine / transmission assembly removal and installation.• Illustrated engine teardown and rebuild, with camshaft and timing

chain replacement, detailing wear limits and nominal values.• Fuel injection and ignition system service and component testing

of different Bosch DME engine management systems, including the secondary air injection (SAI) system.

• Clutch, flywheel and rear main seal service.• Front and rear drivetrain service, including front (C4) and rear

differential service.• Brakes, steering, suspension and ABS maintenance, troubleshooting

and repair for both vacuum boost (C2) and hydraulic-boost (C4) brake systems.

• Heating and air-conditioning repair, including A/C component replacement.

• Body adjustments and repairs, including convertible top, sunroof and targa top service and adjustment.

• Electrical system service, with an easy-to-use illustrated component location section.

• Wiring schematics for selected models, with DME systems, power distribution, grounds, convertible top and other hard-to-find circuits.

BentleyPublishers.com

bentley_p998_new.product.announcement.pdf

Convertible top drive diagnosis and repair, including microswitch location and function.61 Convertible Top

Full maintenance procedures, including drive belt replacement.03 Service and Maintenance

Full color repair procedures

Engines covered:1995: 3.6 liter (M64.07 and M64.08)1996-1998: 3.6 liter (OBD II M64.23 and M64.24)

Transmissions covered:G50 (6-speed manual, RWD)G64 (6-speed manual, AWD)A50 (4-speed automatic)

Fuel pump testing and replacement.20 Fuel Supply