DSG-423 FUEL SYSTEM
04-14
The pinpoint tests below should be performed after the preliminary tests and “Engine Cranks but Will Not Start” chart
Steps 1-3. Any electrical diagnostics should have been performed to eliminate any sensor, GCP or solenoid valve
problems before proceeding.
Engine Starts But Has Rough Idle
Test Step Result Action to Take
1 Check for icing or freezing of the Regulator. Yes
No
The presence of ice on the converter,
with the engine running, indicates the
possibility of a coolant supply problem.
Check Coolant level and the coolant
system for leaks. Check for proper
coolant type
Go to Step 2.
• With the Engine at Idle.
• Check for ice or frost build up on the converter casing and
outlet port.
Is ice present?
2 Check for stuck primer button. Yes
No
Try and free the primer button. If you
cannot reseat the primer then see
section 475R-1 for servicing the
converter.
Go to Step 3.
• Key Off.
• Press the primer button on the converter once to ensure
the primer is not sticking open. A small amount of fuel that
is trapped between the fuel lock and the converter should
pass through to the carburetor.
Is the primer button stuck in the depressed position?
3 Check FCV for operation. Yes
No
This would indicate the engine is too
lean at idle. Possible causes:
• Plugged bypass port, go to Step 4.
• Faulty FCV valve connection, go to
Step 5.
• GCP fault
.
Go to Step 6.
• With the Engine at Idle.
• Disconnect the vacuum hose from the FCV valve to the
regulator.
Does the idle run smooth with the hose disconnected?
4 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 5.
• 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?
5 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.
Go to Step 6.
• Key OFF.
• Disconnect FCV connector from harness.
• With the engine at idle.
• Using a high impedance DVOM, check for 12 volt supply
at the harness connector.
Is the voltage less than 11.5 volts?
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