
RENR9968-02 33
Testing and Adjusting Section
7. Close and tighten the air purge screw.
8. Crank the engine for 30 seconds. Allow the starter
motor to cool for two minutes.
9. Close and tighten the fuel pressure regulating
valve.
Note: Failure to tighten all fittings could result in
serious fuel leaks.
10. Crank the engine for 30 seconds. Allow the starter
motor to cool for two minutes.
11. Repeat Step 10 until the engine starts and runs.
12. Clean any residual fuel from the engine
components.
i02229176
Fuel System Pressure - Test
SMCS Code: 1250-081; 1256-081
Low Fuel P ressure
Low fuel pressure can cause low power. Low fuel
pressurecanalsocausecavitation of the fuel
which can damage the fuel injectors. The following
conditions can cause low fuel pressure:
•
Plugged fuel filters
•
Debris in the check valves for the fuel priming
pump
•
Debris in the pressu re regulating valv e
•
Partially open check valve
•
Sticking or worn fuel pressure regulating valve in
the fuel tra nsfer pump
•
Severe wear on return fuel pressure regulating
valveinthefuelfilter base
•
Worn gears in the fuel transfer pump
•
Pinched fuel lines or undersized fuel lines
•
Old fuel lines that have a reduced interior diameter
that was caused by swelling
•
Fuel lines with deteriorating interior surfaces
•
Pinched fuel line fittings or undersiz ed fuel lin e
fittings
•
Debris in the fuel tank, fuel lines, or fuel system
components that create restrictions
High Fuel Pressure
Excessive fuel pressure can cause fuel filter gaskets
to rupture. The following conditions can c ause high
fuel pressure:
•
Plugged orifices in the fuel pressure regulating
valve
•
Stuck fuel pressure regulating valve in the fuel
transfer pump
•
Pinched fuel return line
Fuel Pressure Readings
The typical fuel pressure of the engine at operating
temperature can vary. At low idle, the fuel pressure
can be 538 kPa (78 psi). At high rpm, the fuel
pressure ca n be 641 kPa (93 psi).
The performance of the unit injector deteriorates
when the fuel pressure drops below 241 kPa (35 psi).
Low power complaints and erratic operation can
occur in this situation. Check for a plugged fuel filte r
or air in the fuel lines as possible causes for t hese
complaints before replacing fuel system components.
Checking Fuel Pressure
Ta b l e 3
Required Tools
Part
Number
Part Name
Quantity
1U-5470
or
198-4240
Engine Pressure Group
or
Digital Pressure Indicator
1
g00294866
Illustra
tion 26
1U-5470 Engine Pressure Group