Checking system pressure, differential pressure and holding pressure — AUDI

Special tools and workshop equipment required

V.A.G 1315 A/1
V.A.G 1318
V.A.G 1318/4
V.A.G 1526 A
V.A.G 1594 A
Measuring container, fuel tight

Test requirements:

Battery voltage at least 11 V

Fuse S17 OK (in fuse box)
Fuel pump relay OK; checking =>Page
25-26
.
Fuel pump OK; checking:

=> Fuel Supply System - Petrol Engines; Repair group 20; Fuel supply
Fuel Supply System - Petrol Engines
Fuel supply

Fuel filter OK
Remote control V.A.G 1348/3A with adapter cable V.A.G 1348/3-2 connected => Page
25-110
.
Pressure gauge V.A.G 1318 with test adapter 1318/4 connected => Page
25-111
.

Important
The fuel system is pressurised. Before opening the system place a cloth around the connection. Then release pressure by carefully loosening the connection.
Checking system pressure and fuel pressure regulator

Open cut-off valve on pressure gauge V.A.G 1318 -Position A-.
Press remote control switch.
Specification: 6.1...6.5 bar

If specification is not attained:

Renew pressure regulator.

If nominal value is exceeded:

Disconnect return hose from pressure regulator at connection of return hose/return line and hold in a container.
Repeat test.

If the specification is attained:

Check that return line is not blocked.

If specification is again exceeded:

Renew pressure regulator.

Checking differential pressure

Close cut-off valve on pressure gauge V.A.G 1318 (lever at right angles to direction of flow).
Detach connector from differential pressure regulator.
Press remote control switch.
Specification of differential pressure:
0.3...0.5 bar below system pressure

If specification not attained or exceeded:

Unscrew thin line -1- on fuel pressure regulator -2- and hold in a measuring container.
Seal connection -3- on fuel pressure regulator.
Press remote control switch.
Specification of overflow volume: 130...150 cm3

Replace fuel pressure regulator, if necessary.
Screw thin line securely back onto fuel pressure regulator.

Set multimeter to measuring range 200 mA and connect to test lead V.A.G 1315 A/1 between differential pressure regulator and connector of differential pressure regulator.
Switch the ignition on.
Press remote control switch.
Specification of differential pressure:
1.2...1.5 bar below system pressure
Specification of differential pressure regulator current: 95...105 mA

If specification for differential pressure is exceeded or not attained:

Replace differential pressure regulator.

If specification for differential pressure and differential pressure regulator current is exceeded or not attained:

With the ignition switched off, use adapter V.A.G 1598/3 to connect test box V.A.G 1598 A only to connector of KE III Jetronic control unit (control unit remains disconnected) => Page
25-16
.

Check for open circuit and short to positive or earth in the following wiring connections:

Connector / Contact · Test box V.A.G 1598 A / Socket
1 · 4
2 · 5

Rectify any open/short circuit as necessary.

=> "Current Flow Diagrams, Electrical Fault-finding and Fitting Locations" binder

If no wiring fault is detected:

Replace KE III Jetronic control unit
=>Page
25-19
.

Checking holding pressure:

Note:

Only carry out following test on vehicles with hot starting problems.

Press switch on remote control for approx. 5 seconds.

Check holding pressure on gauge.
After 10 minutes the remaining pressure should be at least 3.5 bar.
After 20 minutes the remaining pressure should be at least 3.4 bar.

If holding pressure drops below minimum value, the following faults are possible:

Non-return valve in fuel pump defective:

=> Fuel Supply System - Petrol Engines; Repair group 20; Fuel supply
Fuel Supply System - Petrol Engines
Fuel supply

Free play of baffle plate not OK, check =>Page
25-132
.
Check screw connections of injection and fuel lines on fuel distributor for leaks.
Fuel pressure regulator defective

Note:

Before removing the pressure gauge, release fuel pressure at the gauge.