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 1 or 2 psi below manufacturer’s
specification. If the peak flow at idle is less than the calculated
maximum fuel volume requirement, and the capability 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
capability pressure are normal, replace inline filter. If still low,
replace inlet screen/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.
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