Engine Cranking RPM
Figure 1. Diagnostic Form
The Engine Cranking RPM check determines if engine cranking speed is high enough to start the engine and confirms that the CMP (Camshaft Position) sensor is functioning properly. For a reproduction of the applicable portion of the diagnostic form, see Figure .
This is an alternate method to use if the EST is unavailable or fails to function properly. Insufficient electrical power from the batteries or an electronic failure may inhibit the EST from receiving diagnostic data.
The following test must be performed with fully charged batteries.
Engine cranking rpm must be sufficient to generate the required injection control pressure to operate the fuel injectors and to create enough compression heat to ignite the fuel.
The following procedure checks cranking rpm with the breakout box.
- Remove the 60–way engine (upper) connector from the ECM.
- Install the breakout box adaptor connectors to the engine and chassis female connections on the ECM. Reconnect the engine harness connector to the breakout box adaptor connector. Torque the connector to ECM to 35 lb·in.
- Connect the +lead of the Fluke 88 to terminal 51, and the —lead to terminal 19. Select the DC voltage scale and press the RPM button. See Figure
“Measuring Engine Cranking RPM with Breakout Box”
1. Breakout Box
Figure 2. Measuring Engine Cranking RPM with Breakout Box
- Crank the engine while observing the Fluke 88. A minimum of 130 rpm (26 Hz) is necessary to start the engine.
- Record the cranking engine rpm on the diagnostic form.
A “0” frequency indication on the Fluke 88 during engine cranking may indicate the ECM is not receiving a signal from the CMP sensor. Refer to “19.1 Functions”
If the CMP sensor is inoperative, it must be repaired before continuing. The ECM will not allow the IPR (Injector Pressure Regulator) valve to fully activate without a CMP signal.
Note: If no frequency/engine rpm is measured with the Fluke 88, check for additional fault codes. Refer to “19.1 Functions”
for Test 5; and refer to “10.10.2 Test Procedure”
for Test 7.
Possible causes for the hard start/no start diagnosis include:
- Low cranking rpm — The starting system electrical malfunctions. Incorrect oil type or extended oil change intervals in cold ambient temperature conditions.
- No engine rpm — Poor electrical connection at the CMP sensor wiring harness connector, wiring harness to sensor open or shorted. or a defective CMP sensor causing an “0” frequency/engine rpm indication.
Fluke 88 DVOM, J 34520A
, and breakout box, J 43102
, for CMP sensor diagnostics.
|Series 40E Troubleshooting Manual – 6SE241|
|Generated on 10-13-2008|