Related Manuals for Porsche 912E
Summary of Contents for Porsche 912E
- Page 1 TECHNICAL MANUAL L-JETRONIC FUEL INJECTION SYSTEM PORSCHE 912E...
- Page 2 TABLE OF CONTENTS Introduction to L-Jetronic Fuel Injection L-Jetronic Fuel Injection Theory of Operation L-Jetronic Component Identification Operating Conditions Troubleshooting the Porsche 912E Fuel Injection System Component Location System Diagrams and Reference Tables Bibliography...
- Page 3 ETRONIC 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 injection system. Originally, Volkswagen adapted the L-Jetronic for the Type 4 air cooled 411 engines sold in the United States due to more stringent emissions and fuel consumption regulations.
- Page 4 923 615 101 00 0 332 514 103/104/120 Part numbers beginning with 923 are Porsche part numbers. Part numbers beginning with 022 are Volkswagen part numbers. Part numbers beginning with 0, followed by a 3 digit number (0 311 906 041A) are Bosch part numbers.
- Page 5 The following diagram provides an overview of how the fuel injection components are integrated. AIR FLOW ELECTRONIC CONTROL UNIT INJECTORS METER CYL 1 Injection Pulse Amount of Air Draw In CYL 2 Temperature of Air Drawn In CYL 3 THROTTLE PUMP and CYL 4 Engine Load (WOT)
- Page 6 During cold start and all other load conditions, the fuel pressure regulator found in the 912E is able to maintain an equal difference in pressure on all the injector valves regardless of load conditions.
- Page 7 Specific steps for this adjustment are provided in Section 5.0. The 912E throttle valve switch does not provide an input to the electronic control unit during the idle load condition as previously found in the 914 1.8L L-Jetronic Fuel Injection System.
- Page 8 ROUBLESHOOTING THE ORSCHE NJECTION This section is designed to assist the Porsche 912E owner in locating faults in the L-Jetronic system, isolating the component involved and testing the component for correct function. The tools required will include a fuel pressure gauge and fittings, a tachometer, a CO meter and volt-ohmmeter.
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Page 9: Engine Does Not Start
Failures in the L-Jetronics fuel injection system can be categorized into five major categories. The components associated with the potential failures are identified and measurements are provided which will allow the verification of each component’s operating condition. Please refer to the system diagrams provided in section 7.0 to assist in isolating the problem area. - Page 10 ENGINE DOES NOT START (continued) Possible Problem Procedure 1. Connect a pressure gauge to the tee found on the driver’s side of the fuel rail. Disconnect the wire from Cold Start Valve terminal 1 of the ignition coil. Operate starter briefly to build up fuel pressure.
- Page 11 ENGINE DOES NOT START (continued) 1. Check the air-flow sensor function by removing the connection on the back of the sensor. Connect an Air Flow ohmmeter to the following contacts to verify sensor. Sensor Pins 6 and 9 200 – 400 ohms Pins 7 and 8 120 –...
- Page 12 ROUGH ENGINE IDLE (continued) 1. Take the cover off of the throttle valve switch and verify that the Throttle Valve contacts are open with the throttle at Switch idle position. If throttle is placed in wide open position, then the contacts should make and the following reading should be detected.
- Page 13 1. Verify the operation of each injection valve by disconnecting the electrical supply to each injection valve, one at a Fuel Injection Valves time and determine if the engine speed drops when the valve is disconnected. 2. If the speed drops, the valve is defective.
- Page 14 1. Check for engine hesitations caused by loose contacts by moving the wiring harnesses and watching for changes in Connectors and Wiring the rpms. 2. Check wires 5, 6, 17, and 49 for proper continuity to ground. 1. Inspect and check that the harness plugs for the dual relays are in good Voltage condition.
- Page 15 6.0 L OCATION OF 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.
- Page 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 attachment allow easy recognition of this component. • Air flow sensor – Attached between the connecting tube and the air cleaner box.
- Page 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 the injection resistors are collocated with this component. • Electronic Control Unit – Can be found on the bulkhead of the passenger side of the engine compartment.
- Page 18 • Temperature Sensor II – Located next to the spark plug for the 3 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.
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Page 19: Fuel Injection
7.0 S YSTEM IAGRAMS AND EFERENCE ATERIAL This section provides numerous reference diagrams and measurement tables to assist in the diagnosis of L-Jetronic fuel injection problems. Dual Relay Drawing The following drawing is a diagram of the bottom of the dual relay located on the back left side of engine compartment. - Page 20 L-Jetronic System Diagram The next diagram is a schematic drawing of the complete L-Jetronics fuel injection system. This diagram was adapted from the Porsche 912E Workshop Manual and has been enhanced to provide additional information to assist in isolating fuel injection problems.
- Page 21 12Vdc from Ignition Switch (Pin 15) (Red/Black) Tachometer (Purple/Black) 12Vdc from Ignition Electronic Fuel Injection Unit 12Vdc from Switch Ignition (Pin 15) Switch (Pin 50) (Yellow) 12Vdc from Fuse on Rear Fuse Box (red/black) (red) (red) 12Vdc from Pump Relay Battery Contacts 86b 86c 88z...
- Page 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. The following diagram is provided to assist in locating the vacuum hoses in the 912E. Please note that the smog pump injection system is not shown.
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Page 23: Pin Number
The following diagrams of connector plugs are provided to assist in the isolation of fuel injection component failures. Specific characteristics of the connector plugs and reference pins have been identified in order to aid the 912E owner in taking voltage and resistance measurements. It is most often easier to isolate... - Page 24 Temperature Sensor in Air Flow Sensor Can measure between pins 6 and 27 of the ECU connector to verify sensor is functioning Air Flow Sensor Input Can measure between pins 7 and 8 to verify movement of air flap. Air Flow Sensor Input Air Flow Sensor Input Limiting Resistor inside air flow sensor can be...
- Page 25 Not Used Not Used Not Used Not Used Pulses to Injection Valves Pulses to Injection Valves Auxiliary Air Valve 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 valve. There is a small tab on the top of the plug that can be used to assist in identifying the connector pins.
- Page 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.
- Page 27 The following table provides a quick reference for verifying the measurement values for each L-Jetronic fuel injection component. Quick Reference Table - Fuel Injection Component Values Fuel Injector Valves 2 – 3 ohm coil resistance Thermo-time Switch Below 95 F = 0 ohms Above 95 F = Infinite Cold Start Valve Remove cold start valve from manifold and place in a...
- Page 28 The following table provides a quick reference for the Porsche 912E tune-up and adjustment parameters. TUNE - UP PARAMETERS Idle Speed 875 – 975 rpm Ignition Timing BTDC @ 3,500 rpm Spark Plug Gap 0.7mm/0.028 in. Breaker Point Gap 0.4mm/0.016 in.