Vanguard 25E300, Repair Manual

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SPN 633 Vapor Detection in FDI
Circuit Description
The ECM monitors the fuel injector pulse width (the amount of
time the fuel injector is energized or open) to detect vapor in
the injector. Fuel vapor in the injector can be detected during
the engine's cranking state and running state.
The use of high Reid Vapor Pressure (RVP) fuel in high
temperature environments can lead to vapors within the
system. Example: Winter formulated fuel used in summer
conditions.
Possible FMIs - SPN 633
The possible FMIs for SPN 633 are as follows:
FMI Description
8 Vapors detected in FDI during RUN state
11 Vapors detected in FDI during CRANKING state
SPN 633, FMI 8: Vapors Detected in FDI During RUN State
Step Action Yes No
1 Is high RVP (winter blend) fuel being used in a high ambient
temperature environment?
Drain fuel and replace with new. Proceed to Step 2.
2 Are the air cooling passages blocked or dirty? Clean all engine cooling system
components. This includes: blower
housing, fan, cylinder air guides, cylinder
cooling ribs.
Proceed to Step 3.
3 Is the engine being run in a high ambient temperature
environment?
Move engine to cooler surroundings. -
SPN 633, FMI 11: Vapors Detected in FDI During CRANKING State
Step Action Yes No
1 Is high RVP (winter blend) fuel being used in a high ambient
temperature environment?
Drain fuel and replace with new. Proceed to Step 2.
2 Is the engine being asked to start in a high ambient temperature
environment?
Move engine to cooler surroundings. Proceed to Step 3.
3 Was the engine previously running and is now being asked to
restart hot?
Allow the engine to cool prior to
restarting.
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