Fuel Pressure: Testing and Inspection
WARNING!When working with fuel or parts of the fuel system:
^ DO NOT smoke.
^ DO NOT use heaters or have anything else in the area that could ignite fuel.
^ Protect eyes and skin.
^ Always have a fire extinguisher readily available. Be prepared for residual fuel pressure in the system. When loosening fuel line connections:
^ Loosen fittings slowly to allow pressure to be relieved.
^ Be prepared to collect fuel that is discharged.
CAUTION!
^ Always clean fuel line connections and surrounding area before loosening fittings.
^ Always replace seals and fuel hose clamps.
Requirements
- Fuse 17 (in fuse holder) OK
- Fuel filter OK
- Battery: minimum 12 volts available
Checking system fuel pressure
- Remove fuse 17 from fuse holder.
Fuse 17 Terminals 1 & 2 In Fuse Panel:
- Connect remote control VW 1348/3A (using adapter lead VW 1348/3-2 and adapter cables from VW 1594) between:
^ Fuse 17 terminal -2- and
^ Positive (+) remote connection in engine compartment
- Disconnect vacuum hose from fuel pressure regulator.
Fuel Pressure Gauge Set:
- Connect pressure gauge VW 1318 into fuel supply line as shown, using adapters VW 1318P and VW 1318/15.
^ A = Fuel supply line from tank
^ B = Fuel line to fuel rail
Note:
Pressure gauge shut-off valve must be in the open position (lever in direction of flow).
- Activate remote control briefly.
^ Fuel Pump (FP) should operate
Note:
If fuel escapes during the following pressure check of vacuum connection at the fuel pressure regulator, replace the regulator.
If fuel pump does NOT operate:
- Check fuel pump.
If fuel pump does operates:
- Activate remote control, until pressure no longer increases.
^ Must be: 4.0-4.2 bar (58-61 psi) with fuel pump running
^ Must be: 3.4-3.7 bar (49-54 psi) immediately after fuel pump (remote control) is switched OFF
Note:
If NO fuel pressure has built up, check whether fuel hoses (i.e. supply and return) have been transposed.
If specified value is NOT obtained:
- Check fuel pump.
- Check fuel supply line for leaks or damage, such as pinching along vehicle body routing.
- Repair as necessary.
If specified value is still NOT obtained:
- Replace fuel pressure regulator and repeat pressure check. If specified value is exceeded:
- Check return line for damage, such as pinching along vehicle body routing.
- Repair as necessary.
WARNING!
Excessive fuel pressure may:
^ Create risk of explosion
^ Rupture fuel pressure regulator diaphragm
^ Cause fuel to enter engine via fuel pressure regulator vacuum hose
- Disconnect remote control and install fuse 17.
CAUTION!
Do not run the engine unnecessarily, with the vacuum hose to the fuel pressure regulator disconnected. The increased fuel pressure will cause mixture enrichment, which may in turn cause exceeding of oxygen control limits resulting in possible Diagnostic Trouble Code (DTC) storage.
- Run engine at idle.
^ To automatically interrupt Output Diagnostic Test Mode (DTM)
- Switch OFF electrical accessories (A/C, etc.).
^ Coolant fan must not be running during measurements.
- Connect vacuum hose at fuel pressure regulator.
- Observe pressure drop on fuel pressure gauge.
^ Must be approximately 0.5 bar (7 psi).
If NO:
- Check vacuum hose for leaks, cracks or damage.
- Check vacuum connection on intake manifold by disconnecting vacuum hose from fuel pressure regulator and blowing through it.
If there is NO leak (and vacuum connection is NOT blocked):
- Replace fuel pressure regulator.
Checking residual fuel pressure
- Stop engine.
- Wait 10 minutes
- Check residual pressure.
Minimum acceptable pressure values:
- Cold engine: 2.5 bar (36 psi)
- Warm engine: 2.8 bar (41 psi)
Note:
When the engine is hot, fuel pressure is higher. This is a normal condition caused by fuel expansion.
If residual pressure specification is NOT obtained:
- Check pressure tester connection (for leaks).
- Check fuel lines (for leaks).
- Check fuel pump check valve.
- Check fuel injectors for leaks.
If NO leaks are found (and fuel pump check valve is OK):
- Replace fuel pressure regulator.
- Repeat residual pressure test.
Note:
After checking fuel pressures (system and residual pressures), check and erase the Diagnostic Trouble Code (DTC) Memory