C 1500 Truck 2WD V8-6.5L DSL Turbo VIN S (1997)
Positive Crankcase Ventilation Valve: Testing and Inspection
Crankcase Depression Regulator (CDR) Valve Test
The purpose of the CDR valve is to maintain 0 to 4 inches of water vacuum in the crankcase at all engine speeds, assuming that the piston/ring
combustion blow by is not excessive (less than 4 cfm). Too little vacuum will tend to force oil leaks.
The CDR valve is checked with a water manometer. The U-tube manometer indicates pressure or vacuum by the difference in the height of the two
columns of the fluid.
If the crankcase vacuum is too high (greater than 4 inches of water), dirt or dust can more than likely be pulled into the crankcase cavity (pulled through
front/rear crankcase seal, etc.) and contaminate the oil. If the crankcase pressure is positive, engine oil leaks are more than likely to occur around the
engine seals and the gaskets.
1. Connect one end of the manometer to the engine oil dipstick hole. The other end of the manometer is vented to the atmosphere.
2. Unplug the rubber vent tube from the turbo inlet elbow.
3. Run the engine through a no-load speed range (gear selector in PARK) and the observe manometer readings. If the manometer reading is + 4
inches of water or less positive pressure, reconnect the CDR system and proceed to Step 4. If the manometer reading is higher than + 4 inches of
water positive pressure, this indicates that there is an internal engine problem (refer to Engine Mechanical).
4. Install the air cleaner.
5. Start the engine and observe the manometer reading. The manometer reading should read from zero to one inch (0-1 inch) of water (vacuum) at the
idle to approximately 34 inches of water (vacuum) at 2000 RPM. Add the amount that the manometer column travels up, to the amount that the
column travels down in order to obtain the total water pressure (vacuum). An example of a manometer reading is as follows: One-half inch above
zero plus on-half inch below zero equals one inch vacuum reading (1/2 in. +1/2 in. =1 in.).
