Form 824262
Page Number - 31
Appendix D
Returnless (Electronically Regulated)
Fuel System Diagnostic Guide
Scenario 2
Diagnosis:
A restriction to the supply of fuel to the engine such as a clogged
inlet strainer, inline filter, or pinched fuel supply line
will reduce the flow of fuel. However, idle and peak pressure will
remain normal or drop only .05 or .15 bar (1 or 2 psi) (5 or 15
kpa) below manufacturer’s specification. If the peak flow at idle is
less than the calculated maximum fuel volume requirement, and
the peak demand pressure is low then the engine will be starved
of fuel in a heavy-load condition such as wide-open throttle.
Additional Action:
Inspect the fuel supply line for damage. Connect FST between
fuel tank and inline filter, and retest. If the peak flow and peak de-
mand pressure are normal, replace inline filter. If still low, replace
inlet strainer/sock.
Scenario 3, 4, 5
Diagnosis:
If testing with the FST indicates the engine is not receiving the
proper fuel pressure and volume, and a clogged inline filter or
fuel line are determined not to be the cause, then a failure of
the electronic control system or the fuel pump is the most likely
cause. Follow the vehicle manufacturer’s recommended
procedure for troubleshooting these components to determine
the malfunction.
