Checking Pressures

CHECKING PRESSURES











General Information

The tester is mounted in the control line between the fuel distributor and control pressure regulator.






The terminals and lever positions of the changeover valve are numbered in the following text for better understanding.

1979 models do not have a switch on the air flow sensor, so on these cars the circuit operated by the fuel pump relay will have to be bridged

CONNECTING AND BLEEDING PRESSURE GAUGE

Connecting






1. Unscrew control pressure line at fuel distributor.
2. Connect control pressure line to hose line connection 1 of change-over valve.






3. Connect the connection on the fuel distributor with the hose line from connection 3.


Bleeding

1. Disconnect electrical connector at air flow sensor terminal.
2. Disconnect electrical connector at control pressure regulator, so that the control pressure regulator will not heat up.
3. Let pressure gauge hang down (stretched hose line) and turn on ignition.
4. Move operating lever of the change-over valve between positions 2 and 3 about 5 times at intervals of 10 seconds.

CHECKING "COLD" CONTROL PRESSURE


This test must be performed on a cold engine. This test is absolutely essential for starting or warm-up difficulties.

1. Move change-over valve to position 2.






2. Disconnect electrical connector at air flow sensor terminal.
3. Disconnect electrical connector at control pressure regulator, so that the control pressure regulator will not heat up.
4. Turn ignition on.
5. Refer to the graph of the testing and adjusting specifications for pressure data at immediate outside temperatures.
6. Replace the control pressure regulator if measurements are out of specifications.

CHECKING "WARM" CONTROL PRESSURE

Note: Engine can be warm or cold.

1. Move change-over valve to position 2.






2. Connect electrical connector to control pressure regulator.
3. Disconnect electrical connector at air flow sensor terminal.
4. Turn on ignition and allow control pressure regulator to heat up. When needle on gauge stops rising, take reading.
5. The final pressure must correspond with the specification. If not, replace the control pressure regulator.

CHECKING SYSTEM PRESSURE

The fuel supply, electric fuel pump and fuel filter must be in perfect condition for this test.

1. Move change-over valve to position 3.






2. Disconnect electrical connector at air flow sensor terminal.
3. Turn ignition on.
4. If specifications are not met, adjust pressure by changing shims of system pressure regulating piston.

ACTIVATING FUEL PUMP CIRCUIT FOR TESTING (from 1979 model)

Note: Pull electric connectors off of control pressure regulator and auxiliary air regulator, so that these parts will not heat up during subsequent test.

1. Loosen and detach relay plate.






2. Pull fuel pump relay off of relay plate.






3. Bridge terminals 30 and 87 with a piece of wire. Fuel pump should run.

CHECKING FUEL DELIVERY RATE FOR CONTROL PRESSURE CIRCUIT

Testing Requirement: Fuel pump in perfect running condition.

Checking






1. Connect and bleed pressure meter P 378.






2. Turn valve to position 3.






3. Disconnect left hose from special tool P 378 at feed line to control pressure regulator and hold in a measuring glass (capacity at least 500 cc).






4. Turn on ignition. Turn valve to position 2 and let fuel pumps(s) run exactly 1 minute by pulling off two-pin plug on mixture control unit. The fuel pump(s) in cars from 1979 models can be run by supplying battery voltage to multiple-pin plug terminal 7 (red/white) with a piece of wire. The ignition need not be turned on.












5. Stop by turning valve to position 3 and measure delivery rate. Test value: 160 to 240 cc/minute.


If measured value is not same as specified value, the cause is in the fuel distributor. Replace fuel distributor.

CHECKING ENTIRE FUEL SYSTEM FOR LEAKS

Note: Check on a warm engine, but not immediately after engine was run hot.






1. Turn valve to position 2.
2. Turn on ignition. Detach plug on air flow sensor contact. Fuel pump (s) run.






The fuel pump(s) in cars from 1979 models can be run by supplying battery voltage to multiple-pin plug terminal 7 (red/white) with a piece of wire. The ignition need not be turned on.






3. Turn off ignition (detach wire on battery supply from 1979 models) after reaching "warm" control pressure and observe pressure drop on pressure gauge. Pressure will drop quickly at first and then become stabilized. If pressure continues to drop quickly (see testing and adjusting specifications), repeat test with disconnected control pressure circuit to limit possible causes. Turn valve to position 3 for this.

If results are the same, leak is in system pressure circuit.

If results of second test are okay, leak is in control pressure circuit.

Possible Causes in System PressureCircuit:

Check valve of fuel pump leaks.
0-ring in system pressure regulator leaks.
Fuel injectors leak.
Start valve leaks.

Fuel injectors and start valve must be inspected separately. Replace check valve of fuel pump and O-ring of system pressure regulator in fuel distributor separately and repeat test.

Possible Causes in Control Pressure Circuit:

Control pressure regulator leaks.
Control pressure reducing valve leaks.