STI Home
Diagnostic Manual, Engines, Volume 2

 Printable version
 2.1 Gasoline Injection System    >   32 Hydraulic Test Program - Test (Testing Fuel System Pressure and Internal Leakage)

Hydraulic Test Program - Test (Testing Fuel System Pressure and Internal Leakage)

Test Step Test scope Test connection Test condition Nominal value Possible cause/Remedy
1.0 Fuel connections
Check for leakage.

2.0 Check for ease of movement of air flow sensor plate (4) with lever (1) and control plunger (2) in fuel distributor ( 32 , Figure 1).   Switch on ignition briefly to build up fuel pressure.

Depress air flow sensor plate (4) by hand (Figure 1).

Release air flow sensor plate (4) quickly.

Uniform resistance should be felt during its entire travel.

No resistance should be felt since the slow to react control plunger (2) lifts off the lever (1, Figure 1).

Center/replace air flow sensor plate,

Replace air flow sensor.
2.1 Control plunger
Depress air flow sensor plate (4) by hand.

Release air flow sensor plate (4) slowly.

Control plunger (2) should remain in contact with the lever (1).

Replace fuel distributor.
3.0 Check control plunger
(2, Figure 1) in fuel distributor for leakage.

Press air flow sensor plate (4) completely down and hold in this position (illuminate intake with borescope).
Slight seepage (drops) is permissible. Replace fuel distributor.
4.0 Fuel pressures Connect pressure gauge. Connect hose "A" to lower chamber using adaptor (044), connect hose "B" to upper chamber, 31 , Figures 1 or 2.

When connecting pressure gauge, do not contact air flow sensor with wrench.

4.1 System pressure
Engine: at Idle
Valve on pressure gauge open.
6.2 - 6.4 bar Check fuel pump,
Replace diaphragm pressure regulator,
Check fuel return line for restrictions.
4.2 Lower chamber pressure
Engine: at Idle and at operating temperature.
Electrohydraulic actuator connector unplugged, valve on pressure gauge closed.
Approx. 0.4 bar below system pressure. Replace electrohydraulic
actuator (Y1)
5.0 Deceleration shut-off
(Engine 104 only)
Pressure gauge

Engine: at Idle and at operating temperature.
Raise engine speed to 2500 rpm and then close throttle valve.
Lower chamber pressure must increase to system pressure until combustion resumes. Check deceleration shut-off, see 23 37.0.
6.0 Acceleration enrichment Pressure gauge

Ignition: OFF
ECT sensor (B11/2) unplugged. Using two resistance substitution units, simulate 2.5 k resistance (+ 20°C) at sockets 2 and 4 as well as at sockets 1 and 3 ( 32 , Figures 2 and 3).

Engine: at Idle

Rev engine abruptly.
Approx. 0.5 bar below system pressure

Pressure in lower chamber must decrease to < 5.5 bar.
23 1.0 ,
23 10.0 ,
23 14.0.
7.0 Fuel system leakage Pressure gauge

Engine: OFF
System pressure drops below opening pres-sure of injectors to approx.
3.5 bar.
If pressure drops immediately to
0 bar, replace check valve in fuel pump.
If pressure drops slowly below 3.5 bar, 7.1 - 7.4
7.1 Diaphragm pressure regulator
Disconnect fuel return line at diaphragm pressure regulator. No fuel should flow out of diaphragm pressure regulator (slight seepage is permissible).

If fuel flows out of the fuel return line, plug line immediately.
Replace diaphragm pressure regulator.
7.2 Fuel accumulator Pressure gauge

Pinch leak-off line on fuel accumulator.

Fuel pressure should no longer drop.
Replace fuel accumulator.
7.3 Start valve

33 or 34.
7.4 Fuel distributor
Test steps 7.1 - 7.3 ok
Replace fuel distributor.
7.5 External leakage
Disconnect pressure gauge, wiping up any spilt fuel with a rag. Reconnect fuel lines.
Engine: at Idle
All fuel connections must be tight (no leaks).

Table I Fuel pressures

System pressure with engine cold or at operating temperature
bar 6.2 - 6.4
Lower chamber pressure with engine at operating temperature

at a coolant temperature of + 20°C

durind deceleration shut-off
below the previously measured system pressure

at idle, below the previously measured system pressure



approx. 0.4

approx. 0.5

Lower chamber pressure equals system pressure
Sustained system pressure 30 minutes after shutting off engine
bar minimum 2.8