Page Number - 28
Form 824262
Results
Scenario
Idle
Pressure
Peak Flow
(BYPASS)
Peak Demand Pressure
Potential Causes
1
Normal
Normal
2.5 to 4.0 LPM
(.7 to 1.0 GPM)
Normal
Less than
10% below
idle pressure
Fuel system is operating
normally
2
Normal
Low
Less than 2.5 LPM
(.7 GPM)
Low
Greater than
10% below
idle pressure
Blocked fuel filter, inlet strain-
er or supply line
3
Low
Normal
2.5 to 4.0 LPM
(.7 to 1.0 GPM)
Low
Greater than
10% below
manufacturer’s
specification
Faulty pressure regulator
(low pressure)
4
High
Normal
2.5 to 4.0 LPM
(.7 to 1.0 GPM)
High
Above
manufacturer’s
specification
Faulty pressure regulator
(high pressure)
5
Low
Low
Less than 2.5 LPM
(.7 GPM)
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
Fuel Filter
Method 3
External Filtering/External Return
Fuel Return
Method 2
External Filtering/In-Tank Return
Fuel Filter
Pressure Regulator
Fuel Pump
Inlet Strainer/Sock
Fuel Rail
Fuel Supply Line
