Benutzeranleitung / Produktwartung 912E des Produzenten Porsche
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1 TECHNICAL MANUAL L-JETRONIC FUEL INJECTION SYSTEM PORSCHE 912E.
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.
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.
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.
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.
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.
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.
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.
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 .
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 Tempe.
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.
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.
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.
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.
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.
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 Inje.
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.
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