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Manual Porsche 912E

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  • Porsche 912E - page 1

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

  • Porsche 912E - page 2

    2 TABLE OF CONTENTS 1.0 Introduction to L-Jetronic Fuel Injection 2.0 L-Jetronic Fuel Inject ion Theory of Operation 3.0 L-Jetronic Com ponent Identification 4.0 Operating Conditions 5.0 Troubleshooting the Porsche 912E Fuel Injection System 6.0 Component Location 7.0 System Diagrams and Reference Tables 8.0 Bibliography ...

  • Porsche 912E - page 3

    3 1.0 L-J ETRONIC I NTRODUCTION The Bosch L-Jetronic fuel injection system used in the Porsche 912E is often referred to as the Air Flow Controlled or AFC fuel injectio n system. Originally, Volkswagen adapted the L-Jetronic for the Type 4 air cooled 411 engines sold in the United States due to more stri ngent emissions and fuel consumption regulat ...

  • Porsche 912E - page 4

    4 3.0 P ORSCHE 912E L-J ETRONIC C OMPONENTS The following table provides a quick refer ence for the fuel injection components used in the 912E. FUEL INJECTION COMPONENTS FOR THE PORSCHE 912E Component Part Number (1) Fuel Pump 923 601 111 00 0 580 463 010 Fuel Filter 923 110 176 00 0 450 905 001 0 450 905 062 Fuel Regulator 022 906 035 0 280 160 20 ...

  • Porsche 912E - page 5

    5 The following diagram provides an overview of how the fuel injection components are integrated. 4.0 O PERATING C ONDITIONS There are six major operating conditions that the components of the L-Jetronics fuel injection system must detect and provide inputs to t he control unit in order to provide the correct fuel-air mixtur e. These operating cond ...

  • Porsche 912E - page 6

    6 COLD START : When the ignition switch is init ially turned on during the Cold Start phase, it energizes the dual relay se t which provides battery voltage to the control unit and injection valves. W hen the starter is engaged, the relay set provides battery voltage to the electric fuel pump, the cold start valve, the thermo-time switch, and the a ...

  • Porsche 912E - page 7

    7 air during the idle period. This addition al air is obtained via the auxiliary air regulator that provides a bypass around t he throttle valve and allows air to enter directly into the manifold. This bypass route avoids any deflection by the throttle valve. However, the additional intake ai r that is provided through the auxiliary air device, doe ...

  • Porsche 912E - page 8

    8 provides good acceleration response. If sudden acceleration is required during the warm up phase of the engine, the acceleration enrichment provided by the over-swing of the sensor flap may not be sufficient. If this condition is encountered, then the electronic control unit also detects the speed of the deflection of the sensor flap and adj usts ...

  • Porsche 912E - page 9

    9 Failures in the L-Jetronics fuel injection system can be categorized into five major categories. The components associated wit h the potential failures are identified and measurements are provided which wi ll allow the verification of each component’s operating condition . Please refer to the system diagrams provided in section 7.0 to assist in ...

  • Porsche 912E - page 10

    10 ENGINE DOES NOT START (continued) Possible Problem Procedure Cold Start Valve 1. Connect a pressure gauge to the tee found on the driver’s side of the fuel rail. Disconnect the wire from terminal 1 of the ignition coil. Operate starter briefly to build up fuel pressure. Disconnect electrical plug to the cold start valve and apply 12 volts to t ...

  • Porsche 912E - page 11

    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. Connect an ohmmeter to the following cont acts to verify sensor. Pins 6 and 9 200 – 400 ohms Pins 7 and 8 120 – 200 ohms Pins 6 and 27 2k Ohms at room temp (Temp Sensor) Pins 36 and 39. With t he flap ...

  • Porsche 912E - page 12

    12 ROUGH ENGINE ID LE (continued) Throttle Valve Swit ch 1. Take the cover off of the throttle valve switch and verify that the contacts are open with the throttle at idle position. If throttle is placed in wide open position, then the contacts should make and the following reading should be detected. a. Pins 18 and 3 - 0 ohms with throttle valve w ...

  • Porsche 912E - page 13

    13 Fuel Injection Valves 1. Verify the operation of each injection valve by disconnecting the electrical supply to each injection valve, one at a time and determine if the engine speed drops when the valve is disconnected. 2. If the speed drops, the valve is defective. 3. Measure the resist ance of the coil of each injection valve. Should be 2-3 oh ...

  • Porsche 912E - page 14

    14 Connectors and Wiring 1. Check for engine hesitations caused by loose contacts by moving the wiring harnesses and watching for changes in the rpms. 2. Check wires 5, 6, 17, and 49 for proper continuity to ground. Voltage Supply 1. Inspect and check that the harness plugs for the dual relays are in good condition. 2. Verify that there are no volt ...

  • Porsche 912E - page 15

    15 6.0 L OCATION OF C OMPONENTS • Cold start valve – Located on the throttle housing underneath the connector tube. There is a fuel line attached to the cold start valve and allows for easily recognition. • Thermo-Time Switch – Located just below the cold start valve underneath the intake pipe on the passenger’s side. It is distinguished ...

  • Porsche 912E - page 16

    16 • Pressure regulator – This component is located below the air filter box along the back of the engine tin. Tw o fuel lines and the vacuum hose attachment allow easy rec ognition of this component. • Air flow sensor – Attached between the connecting tube and the air cleaner box. • Auxiliary air valve – It is found directly behind the ...

  • Porsche 912E - page 17

    17 • Dual Relay – Located on the bulkhead of the driver’s side of the engine compartment beside the relay plate cove r. The voltage regulator and the injection resistors are collo cated with this component. • Electronic Control Unit – Can be found on the bulkhead of the passenger side of the engine compartment. Eas ily recognized by the l ...

  • Porsche 912E - page 18

    18 • Temperature Sensor II – Located next to the spark plug for the 3 rd cylinder behind rubber cover. • Throttle Valve Switch – Located on the flywheel side of the throttle valve. The cover is removed in this photograph to illustrate the simple contact switch which senses the wide open throttle (WOT) condition only. • The fuel pump is lo ...

  • Porsche 912E - page 19

    19 7.0 S YSTEM D IAGRAMS AND R EFERENCE M ATERIAL This section provides numerous refer ence diagrams and measurement tables to assist in the diagnosis of L-Jetr onic fuel injection problems. Dual Relay Drawing The following drawing is a di agram of the bo ttom of the dual relay located on the back left side of engine compartment. The accompanying t ...

  • Porsche 912E - page 20

    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 is not fused. 88d 12 Volts to Fuel Pump. This output to the fuel pump is available only while crankin g the engine, or after the engine has started, through the pump relay contacts in the air flow sensor. ...

  • Porsche 912E - page 21

    21 Electronic Fuel Injection Unit 42 0 3 4 1 0 6 7 8 9 27 14 15 32 33 13 18 3 2 5 16 17 1 1 Ignition Coil Distributor 2 18 3 Throttle Valve Switch Temperature Sensor II Injector Valves 1 4 3 6 2 Temperature Sensor I Air Flow Meter 27 7 68 9 39 36 Pump Relay Contacts 88b 88a 88c 88b G W Cold Start Valve 86a 86 88y Auxiliary Air Valve Fuel Pump 86b 8 ...

  • Porsche 912E - page 22

    22 Vacuum Hose Diagram Besides air leaks around the air filter box and inta ke hose, vacuum leaks can also lead to poor fuel injection performance. T he following diagram is provided to assist in lo cating the vacuum hoses in the 912E. Please note that the smog pump inject ion system is not shown. Fan Housing Filter Box Charcoal FIlter To Muffler E ...

  • Porsche 912E - page 23

    23 The following diagrams of connector plugs ar e provided to assist in the isolation of fuel injection component failures. S pecific characteristics of the connector plugs and reference pins have been identified in order to aid the 912E owner in taking voltage and resistance m easurements. It is most often easier to isolate the fuel injection prob ...

  • Porsche 912E - page 24

    24 6 Temperature Sensor in Air Flow Sensor Can measure between pins 6 and 27 of the ECU connector to verify sensor is functioni ng 7 Air Flow Sensor Input Can measure between pins 7 and 8 to verify movement of air flap. 8 Air Flow Sensor Input 9 Air Flow Sensor Input Limiting Resistor inside air flow sensor can be measured between pins 7 -9 and 8-9 ...

  • Porsche 912E - page 25

    25 28 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 Thermo-Time Switch Connector Plug – This 2 pin plug can be used to verify the operation of the thermal time switch and the cold start valv e. There is a small tab on the top of the plug that can be used t ...

  • Porsche 912E - page 26

    26 Throttle 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 of the plug. It is best to verify the operation of the throttle valve switch at the ECU plug due to access constraints. 3 NC 18 ...

  • Porsche 912E - page 27

    27 The following table provides a quick re ference for verifying the measurement values for each L-Jetronic fuel injection component. Quick Reference Table - Fue l Injection Component Values Fuel Injector Valves 2 – 3 ohm coil resistance Thermo-time Switch Below 95 0 F = 0 ohms Above 95 0 F = Infinite Cold Start Valve Remove cold start valve from ...

  • Porsche 912E - page 28

    28 The following table provides a quick refe rence for the Porsche 912E tune-up and adjustment parameters. TUNE - UP PARAMETERS Idle Speed 875 – 975 rpm Ignition Timing 27 0 BTDC @ 3,500 rpm Spark Plug Gap 0.7mm/0.028 in. Breaker Point Gap 0.4mm/0.016 in. Dwell Angle 44 0 - 50 0 Valve Clearance Intake 0.15mm/0.006 in. Exhaust 0.20mm/0.008 in. Fir ...

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