Page Number - 38
Results
Scenario
Idle
Pressure
Peak Flow Peak Demand Pressure Potential Causes
1 Normal Normal
.7 to 1.0 GPM
(2.5 to 4.0 LPM)
Normal
Less than
10% below
idle pressure
Fuel system is operating
normally
2 Normal Low
Less than .7 GPM
(2.5 LPM)
Low
Greater than
10% below
idle pressure
Blocked fuel filter, inlet
strainer or supply line
3 Low Normal
.7 to 1.0 GPM
(2.5 to 4.0 LPM)
Low
Greater than
10% below
manufacturer’s
specification
Under-restricting pressure
regulator
4 High Normal
.7 to 1.0 GPM
(2.5 to 4.0 LPM)
High
Above
manufacturer’s
specification
Over-restricting pressure
regulator
5 Low Low
Less than .7 GPM
(2.5 LPM)
Low
Greater than
10% below
manufacturer’s
specification
Failing fuel pump or
insufficient power supply
Appendix C – Returnless (mechanically regulated) Fuel System Diagnostic Guide
Return/Filtration Methods for Mechanically Regulated Returnless Fuel Systems
Method 1
In-Tank Filtering/In-Tank Return
Method 2
External Filtering/In-Tank Return
Method 3
External Filtering/External Return
Fuel Filter
Fuel Filter
Pressure Regulator
Fuel Pump
Inlet Strainer/Sock
Fuel Return
Fuel Rail
Fuel Supply Line
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