DSG-423 FUEL SYSTEM
04-19
Diagnostic Aids
Fuel Line Restrictions
:The vehicle specifications table specifies the fuel line to be a certain size. If the fuel line from
the tank to the fuel lock is not the proper size, or any valves or fittings with flow restrictive characteristics are used,
the fuel flow will not be sufficient to the converter with low tank pressure. Correct any fuel line or fitting restrictions.
Mixer Assembly (Carburetor
):It is possible that a backfire may have caused the fuel valve to partially come off of it's
retainer and restrict fuel, check the mixer fuel valves, see section 475-1 for disassembly. If no other problems have
been identified and the mixer has been serviced, replace the fuel management assembly with a known good part of
the same pressure range. Retest
.
Overall Power Loss
After performing the Preliminary Test, refer to “Unable to reach Full Power” Chart.
6 Check FCV operation. Yes
No
This would indicate the engine is too
lean. Possible causes:
• Plugged bypass port, go to Step 7.
• Faulty FCV valve connection or
vacuum leaks, go to Step 8.
• GCP fault.
Go to Step 9.
• Accelerate engine to induce symptom.
• Disconnect the vacuum hose from the FCV valve to the
regulator.
Does the engine accelerate to full power with the hose
disconnected?
7 Check FCV vacuum fitting bypass port. Yes
No
Clean out bypass with a .050 size pin
or drill bit and retest.
CAUTION: Do not enlarge the by-
pass port.
Go to Step 8.
• The bypass port is located on the back of the 90 degree
elbow which connects the vacuum line from the converter
to the FCV valve.
Is this bypass partially closed with dirt or debris?
8 Check FCV supply voltage. Yes
No
12 volt FCV circuit is open, shorted to
ground or the GCP module is faulty.
Check wiring, connectors and fuses
for possible cause
Refer to section 475-1 for servicing the
carburetor. Also refer to the Diagnostic
Aids below.
• Key OFF.
• Disconnect FCV connector from harness.
• With engine at idle and upon acceleration.
• Using a high impedance DVOM, check for 12 volt supply
at the harness connector.
Is the voltage less than 11.5 volts?
9 Check FCV operation. Yes
No
This would indicate the engine is too
lean. Possible causes:
• Plugged bypass port, go to Step 7.
• Faulty FCV valve connection or
vacuum leaks, go to Step 8.
• GCP fault.
Refer to section 475-1 for servicing the
carburetor. Also refer to the Diagnostic
Aids below.
• Accelerate Engine to induce symptom.
• Disconnect the vacuum hose from the FCV valve to the
regulator.
Does the engine accelerate to full power with the hose
disconnected?
Engine Is Unable To Reach Full Power (Continued)
Test Step Result Action to Take
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