Inspection
| Action
|
DEFINITION: Engine runs unevenly at idle. If severe, the engine or vehicle
may shake. Engine idle speed may vary in RPM. Either condition may be severe enough
to stall the engine.
|
Preliminary Inspection
|
| • | Inspect the vehicle for factory or aftermarket accessories that may contact
the body and chassis. A grounding out condition may simulate a misfire or rough run
concern. |
| • | Compare the scan tool data at idle with the scan tool data list. Refer
to
Scan Tool Data List
. |
| • | Inspect the engine control module (ECM) grounds for being clean, tight,
and in the proper locations. |
|
Sensor Inspection
|
| • | Turn ON the ignition with the engine OFF. Observe the actual fuel rail
pressure with a scan tool. The actual fuel rail pressure should be between 1.0-1.8 MPa.
If it is not, inspect for high resistance in the fuel rail pressure (FRP) sensor circuits
or the FRP sensor. Refer to
Circuit Testing
and
Wiring Repairs
in Wiring Systems. |
| • | Test for an intermittent FRP sensor signal by wiggling the harness between
the sensor and the ECM with the ignition ON and the engine OFF, while monitoring the
parameter with a scan tool. |
| • | Observe the fuel rail pressure (FRP) sensor and the fuel pressure regulator
commanded percent at idle. FRP should be near 40 MPa, and commanded percent
should be near 40 percent. If the command is high, a fuel pressure or sensor
exists. |
| • | Inspect the crankshaft position (CKP) sensor reluctor wheel. Remove the
CKP sensor and attempt to move the reluctor wheel front to back or side to side with
a probe. If there is any movement the reluctor wheel retaining bolts are loose. |
| • | Inspect for proper crankcase ventilation. |
|
Fuel System Inspection
|
| • | Inspect for a sticking Fuel Pressure Regulator. The symptom for this condition
will be an idle surge of at least 100 RPM. This surge will be from 50 RPM
above Desired Idle Speed to 50 RPM below Desired Idle Speed. Refer to
Fuel Pressure Regulator Diagnosis
. |
|
Engine Mechanical Inspection
|
| • | Inspect engine mechanical for the following: |
| - | Sticking or leaking valves |
| - | Excessive oil in the combustion chamber--Leaking valve seals. Refer
to
Oil Consumption Diagnosis
in Engine Mechanical
- 6.6L. |
| • | Inspect the following components for incorrect basic engine parts: |
|
Additional Inspection
|
| • | Inspect the following components of the exhaust system for possible restrictions: |
| - | The exhaust system for damaged or collapsed pipes |
| - | The exhaust manifold for a collapsed inner wall |
| - | The mufflers for heat distress or possible internal failure |
| • | Electromagnetic interference (EMI) on the reference circuit can cause
an engine miss condition. A scan tool can usually detect EMI by monitoring the engine
RPM. A sudden increase in RPM with little change in actual engine RPM change indicates
that EMI is present. If a problem exists, inspect routing of high voltage components,
such as fuel injector wiring, near the sensor circuits. |
| • | Inspect the park neutral position (PNP) switch circuit. |
| • | Inspect for a short to 5 volts on one of the fuel injector control circuit
between the ECM and the FICM. |
| • | Inspect the intake manifold and the exhaust manifold passages for casting
flash. |
| • | Inspect for low engine coolant |
|
