Cranking Speed Check

Tools required: J26999 Compression Gauge
J26999-30 Compression Gauge Adapter

Cranking speed is critical for a diesel to start, either hot or cold. Some tachometers are not accurate at cranking speed. Below is an alternative method of checking cranking speed or determining the accuracy of a tachometer.

1. Screw J26999-30 into any cylinder and connect J26999 gauge.

2. Disconnect the fuel solenoid fuse (F/SOL).

3. Install the digital tachometer to be checked (if desired).

4. Depress the pressure release valve on the compression gauge.

5. With the aid of an assistant, crank the engine for 2 or 3 seconds to allow the starter to reach full speed; then, without stopping. count the number of "puffs" at the compression gage occurring in the 10 seconds following. Multiply the number of "puffs" in the 10 second period by 12 and the resulting number will be the engine speed.

EXAMPLE: 10 seconds = 1/6 of a minute
1 puff = Engine speed of 2
Engine Speed = Number of puffs x 2 x 6 or
Engine Speed = Number of puffs x 12

Minimum cranking speed on the 6.5L diesel engine Is 100 RPM cold and 170-180 RPM hot. The actual engine speed needed will vary depending 6n the condition of the engine (compression) and nozzles.

NOTE:
Refer to Section 6D2 of the Service Manual for diagnosis of cranking system if cranking speed Is too low.

* Alternative method of checking cranking speed is using the Tech 1 as indicated on the video tape that addresses campaign procedures.