Fuel Supply

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GENERAL 201-1

Test equipment 201 -1

Warnings and cautions 201-2

FUEL TANK AND LINES 201-3

Fuel tank, draining 201-3

Fuel tank, removing and installing 201-4

Fuel level sending unit 201-5

Fuel level sending unit, removing and installing 201 -5

Fuel level sending unit, testing 201-6

FUEL PRESSURE CHECKS 201-7

Relieving fuel pressure and connecting fuel pressure gauge 201-7

System pressure, testing 201-7

Fuel delivery volume, testing 201-9

FUEL PUMP ELECTRICAL CHECKS . . .201-9

Fuel pump, troubleshooting 201-9

Operating fuel pump for tests 201 -10

Main/fuel pump relay, testing 201-10

Fuel pump wiring, checking 201-12

Fuel pump current draw, checking 201-13

FUEL PUMP REPLACEMENT 201-13

Fuel pump, replacing 201-13

Fuel pump check valve, replacing 201-14

TABLES

a. Fuel Gauge Sending Unit Specifications 201-6

b. Fuel Pump Pressure Specifications 201-8

c. Fuel Pump Delivery Volume 201-9

Special Tools

Porsche911 Fuel Check Value1984 Porsche 944 High Pressure Hose

Special tool

A Baum 647b Fuel hose pinch clamp

(source: Baum Tools Unlimited)

B Baum 1318 Fuel pressure gauge

(source: Baum Tools Unlimited) C Fluke 87 Automotive digital multimeter

GENERAL

This repair group covers repairs to the fuel tank, fuel pump, fuel level sender and connecting lines. The Motronic (DME) fuel injection and emission control systems are covered in 240 Fuel Injection.

Fuel filter replacement is covered in 030 Maintenance.

Test equipment

A high impedance digital multimeter should be used for all voltage and resistance tests.

^ Some of the procedures require special tools.

Warnings and cautions

Please observe the following cautions and warnings when performing any service or repair on the fuel system.

• When working on an open fuel system, wear suitable hand protection, as prolonged contact with fuel can cause illnesses and skin disorders.

• Gasoline is highly flammable and its vapors are explosive. Do not smoke or work on a car near heaters or other fire hazards when diagnosing and repairing fuel system problems. Have a fire extinguisher available in case of an emergency.

• Disconnecting power from the engine control module (ECM) erases its adaptive memory. It may be necessary to drive the car for approximately 10 minutes after reconnecting the battery to re-set ECM adaptive memory and restore normal performance.

• Always unscrew the fuel tank cap to release pressure in the tank before working on the tank or lines.

• Before making any electrical tests with the ignition turned on, disable the ignition system as described in 280 Ignition System.

• To prevent damage to the ignition system or the electronic fuel system components, including the ECM, always connect and disconnect wires and test equipment with the ignition off.

• Fuse and relay locations are subject to change. Use care when troubleshooting the electrical system at the fuse/relay panels. To resolve problems in identifying a relay, consult an authorized Porsche dealer for the latest information

• Absolute cleanliness is essential when working with the fuel system. Even a minute particle of dirt can cause trouble if it reaches an injector. Thoroughly clean the fuel line unions before disconnecting any of the lines.

• Use only clean tools. Keep removed components dean and sealed or covered with a dean, lint-free shop towel, especially if completion of the repair is delayed.

• When replacing parts, install only new, clean components.

• Avoid nearby use of compressed air, and do not move the car while the fuel system is open.

• Do not use compressed air above 40 psi to blow out lines or components. Internal damage may result to components.

• Always replace seals and O-rings.

FUEL TANK AND LINES

Fuel Tank Capacity

• 1984 -1989 Porsche Carrera .. .22.5 US gals. (85 liters)

The fuel tank is located at the front of the car beneath the luggage compartment. The fuel level sending unit is mounted through the top of the tank. Connecting lines for the evaporative emission control system and fuel supply and return lines are also attached to the tank.

Porsche 964 Fuel Tank Level Reset

Fuel tank assembly

0018702

1.

Fuel tank

2.

Fuel level sending unit

3.

Fuel pump

4.

Fuel pump check valve

5.

Fuel supply line

(to fuel injection system)

6.

Clamp

7.

Fuel pump mounting assembly

8.

Return line

9.

Drain plug/screen filter

10.

Connecting hose

11.

Clamp

12.

Connecting hose

13.

Filler neck bellows

14.

Circlip

1988 Porsche 911 Fuel Line

Wrap iflËlitJWWi.i.Llil . 0018551

CAUTION—

Avoid getting tools or clothing near the battery. Battery electrolyte is a corrosive acid. Always wear eye protection when working on or near the battery.

Fuel tank, draining

^ Unsnap luggage compartment floor carpet (arrows) and lift off. Remove spare tire.

— Disconnect negative (-) battery cable and cover battery terminal to keep cable from accidentally contacting terminal.

— Remove fuel level sending unit as described later.

Wrap iflËlitJWWi.i.Llil . 0018551

— Insert hose into tank opening and use an approved transfer pump and container to pump out fuel.

Be sure the container is large enough to hold the volume of fuel that is to be pumped out of the tank.

As an alternative, the drain plug (alien head) at the bottom of the fuel tank can be removed to drain tank.

- Use a large funnel and drum to catch draining fuel.

- Clean out filter element before reinstalling.

Tightening torques

Clean Porsche Drains Battery Front

Make sure the car is stable and well supported at all times. Use a professional automotive lift or jack stands designed for the purpose. A floor jack is not adequate support.

CAUTION—

Prior to disconnecting the battery, read the battery disconnection cautions given at the front of this manual on page viii.

— Raise car and support in a safe manner.

^ Working underneath front of car, remove stone guard mounting bolts (arrow). Remove stone guard.

^ Pinch off fuel feed line from tank (arrow) with a fuel line clamp.

— Disconnect battery negative (-) cable.

Fuel tank, removing and installing

The fuel tank must be completely drained as described earlier before it is removed from the car.

Porsche 996 Fuel Tank Sendingt

^ Working inside luggage compartment, detach hose from tank vent (arrow).

Porsche 911 Luggage Compartment

Fuel level — sending unit

^ Remove tank mounting bolts (arrows).

— Loosen filler neck clamps.

— Remove fuel tank by lifting it up and out through luggage compartment.

— Installation is reverse of removal.

• Always use new tank mounting gasket and hose clamps.

• Inspect all rubber parts including hoses and replace any that are worn, chafed, or cracked.

Tightening torques

1984 Porsche 944 Fuel Tank Sending Unit

Fuel level sending unit

The fuel level sending unit is mounted in the top of the fuel tank. The unit has a float connected to a variable resistance for fuel level, and a switch that closes to turn on the low fuel light. When replacing the sending unit always replace hose clamps, gaskets and O-rings.

Fuel level sending unit, removing and installing

Unsnap luggage compartment floor carpet (arrows) and remove carpet.

Replacing Porsche 911 Window Switch

0018552

Porsche 993 Battery Test Drain

— Disconnect negative (-) battery cable and cover battery terminal to keep cable from accidentally contacting terminal.

CAUTION—

Avoid getting tools or clothing near the battery. Battery electrolyte is a corrosive acid. Always wear eye protection when working on or near the battery.

^ Remove nuts and washers (arrows) mounting sending unit to tank. Remove harness connector cover (A).

— Disconnect sending unit harness connector.

Slowly withdraw sending unit from fuel tank, allowing it to drain as it is being removed.

— Test unit as described below.

— When reinstalling use a new gasket.

New replacement fuel level sending units from Porsche may be fitted with a guard for protection during shipping. This guard must be removed prior to installing the unit.

Tightening Torques

• Fuel level sending unit to fuel tank 2 Nm (18 in-lb)

— Reconnect harness connector. Fill fuel tank and check for leaks.

Fuel level sending unit, testing

^ Test sending unit using an ohmmeter connected across terminals. Compare results to specification in Table a.

Table a. Fuel Gauge Sending Unit Specifications

Connector terminals

Float position

Test results in Q.

G and 31

Empty

71.7 ±2.3

G and 31

Full

3.2 ± 0.7

G and 31

Slowly tilting removed sending unit to move internal float from empty to full

Resistance continuously changing

W and 31

Empty low fuel light on

Continuity

Fuel Injection Pressure Regulator 911

0018552

1984 Porsche 911 Rscs Injection Pump

When removing test port cap, note small sealing ball under cap. Be careful not to drop sealing ball.

FUEL PRESSURE CHECKS

The fuel pump delivers fuel at high pressure to the fuel injection system. A pressure regulator maintains system pressure. The quantity of fuel supplied exceeds demand, so excess fuel returns to the fuel tank via a return line.

There are three significant fuel pressure and delivery checks:

• System pressure is created by the fuel pump and maintained by the pressure regulator.

• Fuel delivery volume is created by the fuel pump and affected by restrictions, such as clogged fuel filter.

• Residual pressure is maintained in the closed system after the engine and fuel pump are shut off.

Testing for residual pressure is covered in 240 Fuel Injection.

Relieving fuel pressure and connecting fuel pressure gauge

To prevent fuel from spraying on a hot engine, system pressure should be relieved before disconnecting fuel lines. One method is to tightly wrap a shop towel around a fuel line fitting and loosen or disconnect the fitting.

^ Connect fuel gauge (Porsche special tool P 378 or equivalent) to fuel rail test port (arrow) and tighten to 12 Nm (9 ft-Ib).

The fuel pressure gauge should have a range of 0 to 5 bar (0 to 75 psi).

System pressure, testing

^ Fuel system pressure is created by the fuel pump and regulated by the fuel pressure regulator. System pressure is not adjustable.

Fuel pressure regulator

434775 Adapter

Vacuum connection to intake manifold

Spring

Diaphragm

From fuel loop

Return to fuel tank

0018416

Vacuum connection to intake manifold

Spring

Diaphragm

From fuel loop

Return to fuel tank

0018416

Fuel pressure regulator

Porsche 964 Turbo Fuel Regulator Setting

^ Relieve fuel pressure and connect pressure gauge to fuel rail (arrow) as described earlier.

CAUTION—

The fuel pump is capable of developing a higher pressure than that regulated by the pressure regulator. If the fuel pump check-valve malfunctions (stuck closed), make sure the fuel pressure does not rise above 6.0 bar (87 psi). Damage to the fuel lines or fuel system components could result.

— Operate fuel pump without running engine using a fuel pump relay jumper, as described later under Operating fuel pump for tests.

• Check that fuel pressure corresponds to specifications listed in Table b.

• If system pressure is low, repeat test while gradually pinching off return hose. Pressure should rise rapidly. If not, fuel pump is most likely faulty. If pressure does rise, fuel pressure regulator is faulty. See 240 Fuel Injection for replacement information.

• If system pressure is too high, check return line from pressure regulator to tank. Check for kinks in hose. Blow compressed air through line to check for blockages.

CAUTION—

Do not use compressed air above 40 psi to blow out lines or components. Internal damage to components may result.

Fuel Injection Pressure Regulator 911

— Remove fuel pump relay jumper and reattach relay to harness. Start engine and recheck fuel pressure.

• Remove vacuum hose from fuel pressure regulator. Re-check fuel pressure. Compare to specifications in Table b.

• If any faults are found, either fuel pressure regulator or vacuum hose is faulty and should be replaced.

^ When finished testing, disconnect pressure gauge and reinstall fuel pressure test port cap with sealing ball.

Tightening Torque

Table b. Fuel Pump Pressure Specifications

Condition

Fuel pressure

Engine off

2.5 bar (36 psi)

Engine running

Engine running, vacuum hose removed from pressure regulator

2.3 - 2.7 bar (33 - 39 psi)

Psi Fuel Pump

Main/fuel pump relay electrical circuit

Battery to oxygen sensor

Main/ fuel pump relay

Main/ fuel pump relay

yjr-

£3 r-co

CO

87 85

control unit (ECM)

20 1 fuel pump i

control

.0 8r 11.0 bk battery power with key on

WIRING COLOR CODE

bk

black

br

brown

rd

red

yl

yellow

gn

green

bu

blue

vi

violet

gy

grey

wt

white

pk

pink

i, fuse ' ltj9sage „3 i compartment I fusebox #1

Fuel Pump

Fuel delivery volume, testing

Disconnect return line from fuel rail on rear left side of engine (arrow).

To prevent fuel from spraying on a hot engine, system pressure should be relieved before disconnecting fuel lines. One method is to tightly wrap a shop towel around a fuel line fitting and loosen or disconnect the fitting.

Connect a length of hose with threaded female fitting (14mm x 1.5) to fuel rail. Place open end of hose in a suitable container for catching fuel (2-quart capacity).

Run fuel pump for exactly 30 seconds as described earlier under Operating fuel pump for tests and measure fuel collected. Compare to specification in Table c.

When finished testing, reconnect fuel line. Tighten all hose clamps.

Table c. Fuel Pump Delivery Volume

Delivery condition

Delivery rate

30 seconds @ 12V

0.850 liter (0.90 qt.)

FUEL PUMP ELECTRICAL CHECKS Fuel pump, troubleshooting

During cranking and engine running, the DME main/fuel pump relay is energized and the pump runs. If an electrical system fault interrupts power to the fuel pump, the engine will not run.

To quickly check if fuel pump is coming on, actuate starter while an assistant listens for a running pump.

If pump is not running, check for faulty fuse or faulty DME main/fuel pump relay.

• Check fuel pump fuses. See 971 Electrical Component Locations.

• Test DME main/fuel pump relay and circuit as described later.

• Check if voltage is reaching pump. See Fuel pump wiring, checking.

Operating fuel pump for tests

To operate fuel pump for testing purposes without having to run engine, the DME main/fuel pump relay can be bypassed to power pump directly.

— Disconnect DME main/fuel pump relay. Relay is located under driver's seat.

CAUTION—

Disconnecting power from the engine control module (ECM) erases its adaptive memory. It may be necessary to drive the car for approximately 10 minutes after reconnecting the battery to reset ECM adaptive memory and restore normal performance.

^ Connect socket for relay terminal 30 to socket for relay terminal 87b with fused jumper wire to run pump. Ignition key does not need to be turned on.

— After completing tests, remove jumper wire.

CAUTION—

The main/fuel pump relay has a 4 mm2 red wire at terminal 30 in the relay socket. Terminal 87b has a 2.5 mm2 red/green wire. See 970 Electrical Wiring Diagrams for additional wiring information.

The jumper wire should be 1.5 mm2 (14 gauge) and include an in-line fuse holder with a 15 amp fuse. To avoid harness connector damage from repeated connecting and disconnecting, also include a toggle switch.

DME main/fuel pump relay, testing

^ The DME main/fuel pump relay (arrow) is located under the driver's seat next to the engine control module (ECM).

The DME main/fuel pump relay contains two relays within a single housing. One relay is the DME main relay and the other is the fuel pump relay.

Relais Dme Porsche 964

0018558

Horn Relay 987 Boxster

Ö018559

Main/fuel pump relay pins

Main/fuel pump relay circuit

Main/fuel pump relay pins

o

J

©2 to

87 30

©4 3©

1

©6 5©

O 85b

The Motronic DME main relay is energized when the key is turned on. The closed main relay supplies positive battery voltage (via terminal 87) to the fuel injectors, the engine control module (ECM), the idle speed control valve, and the fuel pump relay. The fuel pump relay is then energized (closed) by the ECM. The switched ground for this relay (terminal 85b) is supplied only if certain parameters are met, such as the presence of an ignition pulse and a starter input signal. This is a safety feature to prevent the pump from operating if the engine is not running.

CAUTION—

On cars with a factory alarm (alarm key on door edge), the alarm system interrupts power to terminal 86 of the main/fuel pump relay when the system is armed. When diagnosing a no-start condition be sure to check for key-on power at terminal 86.

— Remove driver's seat. See 720 Seats.

— With ignition switch in OFF position, remove DME main/fuel pump relay harness connector.

— With key off, check for battery voltage at terminal 30 in harness connector.

• If battery voltage is not present, check for breaks in large red wire in relay harness. This wire is a direct (un-fused) connection to battery. See 970 Electrical Wiring Diagrams.

— With ignition switch in ON position check for battery voltage at terminal 86.

• If battery voltage is not present, check for break in black wire in relay harness. See 970 Electrical Wiring Diagrams.

The vehicle alarm system interrupts power to terminal 86. When diagnosing a no-start condition be sure to test key-on power to terminal 86.

Porsche 911 1984 Fuel Line

Check for ground at terminal 85.

• If ground is present continue testing.

• If ground is not present, check connections at ground point on intake runner 1 (arrow).

— Turn off ignition and reattach relay harness connector.

— With ignition switch in ON position and relay connected, check for battery voltage at terminal 87.

• If battery voltage is present, first relay has energized and is functioning correctly.

• If battery voltage is not present and all earlier tests are OK, replace DME main/fuel pump relay.

Fuel Pump Relay Porsche

— If DME main relay has energized but fuel pump still won't run, test fuel pump relay ground and output. Relay must be plugged into harness for test.

• With engine cranking, test for ground at terminal 85b.

• With engine cranking check for battery voltage at terminal 87b.

• If battery voltage is not present at terminal 87b but is present at terminal 87, replace DME main/fuel pump relay.

^ If battery voltage is present but fuel pump doesn't run, check fuel pump fuse (arrow) in luggage compartment fuse box. See 971 Electrical Component Locations.

924 Turbo Relay Fuel Pump

Fuel pump wiring, checking

If fuel pump fuse and DME main/fuel pump relay are OK, but fuel pump will not run, check for voltage at pump.

— Raise car and support in a safe manner.

CAUTION—

Make sure the car is stable and well supported at all times. Use a professional automotive lift or jack stands designed for the purpose. A floor jack is not adequate support.

^ Working underneath front of car, remove stone guard mounting bolts (arrow). Remove stone guard.

— Working at fuel pump, pull back two rubber boots that protect fuel pump electrical connectors.

^ With fuel pump relay bypassed as described above, check for voltage between fuel pump connectors.

• If battery voltage is present and connectors are not loose or corroded, then fuel pump is faulty.

• If there is no voltage, look for a faulty wire or connector.

— Also check fuel pump ground wire (brown wire) for continuity to ground.

Porsche Ground Wire

0018547

Fuel pump current draw, checking

— Raise car and support in a safe manner.

0018547

— Puli back two protective rubber boots from pump connectors. Disconnect 2.5 mm2 red wire from pump.

^ Connect ammeter between disconnected red wire and fuel pump terminal as shown. The other wire remains connected to pump.

CAUTION—

Do not allow the test leads to short to ground.

— Bypass fuel pump relay as described earlier. Fuel pump current should be in the range of 4 to 6 amps.

A higher than normal power consumption usually indicates a worn fuel pump, which may cause intermittent fuel starvation due to pump overheating and seizure. The only remedy is to replace the pump.

FUEL PUMP REPLACEMENT

The fuel pump is mounted beneath the car, behind fuel tank (arrow).

Fuel pump, replacing

— Disconnect negative (-) battery cable and cover battery terminal to keep cable from accidentally contacting terminal.

Make sure the car is stable and well supported at all times. Use a professional automotive lift or jack stands designed for the purpose. A floor jack is not adequate support.

Working underneath front of car, remove stone guard mounting bolts (arrow). Remove stone guard.

Avoid getting tools or clothing near the battery. Battery electrolyte is a corrosive acid. Always wear eye protection when working on or near the battery.

Well Cap Liftng Clamp

0013561

— Raise car and support in a safe manner.

Make sure the car is stable and well supported at all times. Use a professional automotive lift or jack stands designed for the purpose. A floor jack is not adequate support.

^ Working underneath front of car, remove stone guard mounting bolts (arrow). Remove stone guard.

0018547

Fuel Line Tank Porsche 911

^ Pinch off fuel feed line (arrow) from tank with a fuel line clamp.

— Disconnect two electrical wires from pump.

— Remove pressure side fuel line cap nut while counter holding pump fitting with wrench.

— Loosen pump mounting clamp and remove pump.

— Installation is reverse of removal.

Always replace sealing washers. Tightening Torques

• Electrical connector nuts 1.5 Nm (13 in-lbs)

• Stone guard to body (M10 bolt) 47 Nm (35 ft-lb)

• Stone guard to subframe (M10 nut) 28 Nm (21 ft-lb)

Fuel pump check valve, replacing

— Access fuel pump and pinch off fuel feed line as described earlier.

— Remove pressure side fuel line cap while counterholding pump fitting with wrench.

Remove check valve (arrow) from end of pump.

• Replace copper sealing rings during reassembly.

• Start engine and check for leaks after tightening fittings, before reinstalling stone guard.

1984 Porsche 911 Horn Pic

0018547

0018755

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