NOTE: THIS BULLETIN APPLIES TO VEHICLE EQUIPPED WITH A 3.9L, 5.2L. OR11. If an internal vacuum leak is present then perform the Repair Procedure
5.9L GASOLINE ENGINE.
An engine intake manifold plenum pan gasket oil leak may occur on some V-6 and V-8
style engines. The oil leak is internal to the engine so no external oil leakage will be
present. Two symptoms of this oil leak condition may be present. The vehicle operator
may experience an engine spark knock during acceleration and/or an increase in the
amount of engine oil consumed by the engine.
Make sure Technical Service Bulletin (TSB) 18-48-98 has been performed.
NOTE: IT IS IMPORTANT THAT THE COIL AND SPARK PLUG WIRES ARE ROUTED
EXACTLY AS SPECIFIED IN TSB 18-48-98 TO ACHIEVE THE MOST
Inspect the Positive Crankcase Ventilation (PCV) valve. Shake the PCV valve to verify
that the pintle inside of the PCV valve is free. Replace the PVC if the pintle is not free.
If the intake manifold plenum pan gasket is leaking, an additional vacuum source will be
created inside of the engine at the location of the pan gasket leakage. Engine combustion
blow-by gases, oil vapor, and air from the crankcase filter/breather may be drawn past the
leaking pan gasket and into the intake manifold. In most cases when this condition occurs,
an engine at idle will create the highest vacuum and lowest amount of engine blow-by.
1. Allow the engine to reach normal operating temperature.
2. Stop the engine.
3. Disconnect the breather hose from the air cleaner.
4. Attach a vacuum / pressure gauge to the end of the breather hose.
5. Disconnect the PCV valve hose from the intake manifold.
6. Seal off the intake manifold PCV valve hose port opening.
7. Seal off the open end of the PCV valve hose (Figure 2).
NOTE: DURING THIS DIAGNOSIS, IT WOULD BE NORMAL FOR THE ENGINE TO
DEVELOP PRESSURE WITHIN THE ENGINE CRANKCASE. THIS IS DUE TO
THE NORMAL PROCESS OF EXHAUST BLOW-BY GASES LEAKING PAST
THE ENGINE PISTON RINGS AND ACCUMULATING IN THE ENGINE
CRANKCASE. DO NOT ALLOW MORE THAN 3 PSI (20.7 kPa) OF
PRESSURE TO BUILD WITHIN THE ENGINE WHEN PERFORMING THE
FOLLOWING DIAGNOSTIC PROCEDURE.
8. Start the warmed engine and observe the vacuum gauge.
9. Allow the engine to idle for approximately 30 seconds. Do not allow more than 3 psi
(20.7 kPa) of pressure to develop in the engine crankcase.
10.If the attached vacuum / pressure gauge does not indicate that a vacuum is present in
the engine crankcase, then the intake manifold plenum pan gasket is good and no
further internal engine vacuum leak diagnosis is required.