PleasureCraft Engine Group 5.0L, Diagnostic Manual, Page: 271 / 337

5.0/5.7/6.0/8.1L Diagnosis 5 - 129
MEFI 4 - PCM
Diagnostic Aids
Check for the following conditions:
•
Camshaft reluctor wheel damage
•
The sensor coming in contact with the reluctor wheel
•
A cracked or damaged sensor
•
Foreign material passing between the sensor and
reluctor wheel
If you fi nd damage to the reluctor wheel, refer to Camshaft
Replacement in Engine Mechanical (6.0/8.1L).
If you fi nd damage to the reluctor wheel, refer to
Distributor Replacement in Engine Mechanical (5.7L).
If the condition is suspected to be intermittent, check for
poor connections in the harness. Inspect the harness
connectors for backed out terminals, improper mating,
broken locks, improperly formed or damaged terminals
and poor terminal to wire connection.
Test Description
2. This test checks for the 12 volt supply voltage to the
CMP sensor.
3. This test verifi es the ground circuit to the CMP sensor.
Circuit Description
The CMP sensor works in conjunction with a 1X reluctor
wheel on the camshaft (6.0/8.1L), or the distributor shaft
(5.7L). The CMP sensor is a three-wire sensor; 12 volt
supply (depspower), reference ground (depslo) and a signal
circuit.
The CMP sensor determines whether a cylinder is on a fi ring
stroke or on an exhaust stroke. As the camshaft rotates,
the reluctor wheel interrupts a magnetic fi eld produced by
a magnet within the sensor. The sensor’s internal circuitry
detects this and produces a signal which the ECM reads.
The ECM uses this 1X signal in combination with the
crankshaft position (CKP) sensor 24X (6.0/8.1L), or 4X
(5.0/5.7L) signal in order to determine crankshaft position
and stroke.
Observe that as long as the ECM receives the CKP sensor
24X (6.0/8.1L), or 4X (5.0/5.7L) signal, the engine will start.
The ECM can determine top dead center for all cylinders by
using the CKP sensor 24X (6.0/8.1L), or 4X (5.0/5.7L) signal
alone. The CMP sensor 1X signal is used by the ECM to
determine if the cylinder at top dead center is on the fi ring
stroke or the exhaust stroke. If the ECM does not detect a
signal from the 6.0/8.1L CMP sensor, the ECM goes into a
“waste spark” system. A slightly longer cranking time may
be a symptom of this condition. If the ECM does not detect
a signal from the 5.0/5.7L CMP sensor, the only effect is
power balance function of a scan tool will not operate. The
CMP sensor signal is used in diagnostics in order to perform
a Cylinder Balance Test, using a scan tool.
DTC 81 - Camshaft Position (CMP) Sensor Circuit Fault
Step Action Value Yes No
1
Was the “On-Board Diagnostic” (OBD) system check Go to OBD
performed? — Go to Step 2 System Check
1. Install a scan tool.
2. Clear Diagnostic Trouble Codes. Intermittent
2
3. Crank or start the engine. If the engine will not start, Problem
do not crank the engine for more than 20 seconds.
4. Check for diagnostic trouble codes. Go to
Is DTC 81 (CMP Sensor Circuit Fault) present? — Go to Step 3 Diagnostic Aids
Caution: Before proceeding, remove all injector
connectors and the ignition module connector
(5.0/5.7),or disconnect the harness connectors
at the ignition coils and the injectors in order to prevent
personal injury from engine rotation, sparks and
excessive engine fueling.
3
1. Turn “ON” the ignition, leaving the engine “OFF.”
2. Disconnect the Camshaft Position (CMP) sensor
harness connector.
3. Using a DMM connected to a known good ground,
measure the voltage at terminal “A” (8.1L), or “C”
(5.0/5.7/6.0L) (Depspower) of the CMP sensor harness.
Does the DMM display the specifi ed value? 11-13 volts Go to Step 4 Go to Step 9