Porsche 912E User Manual

1 TECHNICAL MANUAL L-JETRONIC FUEL INJECTION SYSTEM PORSCHE 912E

10ENGINE DOES NOT START (continued) Possible Problem Procedure Cold Start Valve 1. Connect a pressure gauge to the tee found on the driver’s side

11 ENGINE DOES NOT START (continued) Air Flow Sensor 1. Check the air-flow sensor function by removing the connection on the back of the sensor.

12ROUGH ENGINE IDLE (continued) Throttle Valve Switch 1. Take the cover off of the throttle valve switch and verify that the contacts are open wit

13 Fuel Injection Valves 1. Verify the operation of each injection valve by disconnecting the electrical supply to each injection valve, one at a t

14 Connectors and Wiring 1. Check for engine hesitations caused by loose contacts by moving the wiring harnesses and watching for changes in the rp

15 6.0 LOCATION OF COMPONENTS • Cold start valve – Located on the throttle housing underneath the connector tube. There is a fuel line attached

16 • Pressure regulator – This component is located below the air filter box along the back of the engine tin. Two fuel lines and the vacuum hose a

17 • Dual Relay – Located on the bulkhead of the driver’s side of the engine compartment beside the relay plate cover. The voltage regulator and t

18 • Temperature Sensor II – Located next to the spark plug for the 3rd cylinder behind rubber cover. • Throttle Valve Switch – Located on the fly

19 7.0 SYSTEM DIAGRAMS AND REFERENCE MATERIAL This section provides numerous reference diagrams and measurement tables to assist in the diagnosis of

2 TABLE OF CONTENTS 1.0 Introduction to L-Jetronic Fuel Injection 2.0 L-Jetronic Fuel Injection Theory of Operation 3.0 L-Jetronic Component I

20 DUAL RELAY TERMINAL PIN FUNCTION TABLE RELAY TERMINAL PIN FUNCTION 88Y 12 Volts from Battery via the regulator and rear fuse panel. This line

21Electronic Fuel Injection Unit420 3410 6 78 9 27 14 15 32 33 13 18 3 2 5 16 17 11IgnitionCoilDistributor218 3ThrottleValveSwitchTemperatureSensor I

22 Vacuum Hose Diagram Besides air leaks around the air filter box and intake hose, vacuum leaks can also lead to poor fuel injection performance.

23 The following diagrams of connector plugs are provided to assist in the isolation of fuel injection component failures. Specific characteristics

24 6 Temperature Sensor in Air Flow Sensor Can measure between pins 6 and 27 of the ECU connector to verify sensor is functioning 7 Air Flow Sensor

2528 Not Used 29 Not Used 30 Not Used 31 Not Used 32 Pulses to Injection Valves 33 Pulses to Injection Valves 34 Auxiliary Air Valve 35 Ground

26Throttle Valve Switch Connector Plug – This 3 pin connector has only two functional pins, 18 and 3. Pin 2 is no longer used and is not even part o

27The following table provides a quick reference for verifying the measurement values for each L-Jetronic fuel injection component. Quick Reference

28The following table provides a quick reference for the Porsche 912E tune-up and adjustment parameters. TUNE - UP PARAMETERS Idle Speed 875 – 975

31.0 L-JETRONIC INTRODUCTION The Bosch L-Jetronic fuel injection system used in the Porsche 912E is often referred to as the Air Flow Controlled or A

43.0 PORSCHE 912E L-JETRONIC COMPONENTS The following table provides a quick reference for the fuel injection components used in the 912E. FUEL I

5The following diagram provides an overview of how the fuel injection components are integrated. 4.0 OPERATING CONDITIONS There are six major ope

6COLD START: When the ignition switch is initially turned on during the Cold Start phase, it energizes the dual relay set which provides battery volt

7air during the idle period. This additional air is obtained via the auxiliary air regulator that provides a bypass around the throttle valve and al

8provides good acceleration response. If sudden acceleration is required during the warm up phase of the engine, the acceleration enrichment provide

9Failures in the L-Jetronics fuel injection system can be categorized into five major categories. The components associated with the potential failu