Inspection
| Action
|
DEFINITION: The engine has a power variation under a steady throttle or cruise.
The vehicle seems to speed up and slow down with no change in the accelerator pedal.
|
Preliminary Inspection
|
| • | Ensure the driver understands the torque converter clutch (TCC) operation. |
| • | Ensure the driver understands the A/C compressor operation. |
| • | Compare the scan tool data at idle with the scan tool data list. Refer
to
Scan Tool Data List
. |
| • | Use the scan tool to ensure the vehicle speed sensor (VSS) reading matches
the speedometer. This excludes vehicles with electronic transmissions where some variation
between VSS and the speedometer is normal. |
|
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 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. |
|
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 System Diagnosis - High Pressure Side
. |
|
Additional Inspection
|
| • | Inspect the fuel injection control circuits between the engine control
module (ECM) and the fuel injection control module (FICM) for a short to a 5-volt
reference circuit. |
| • | Inspect the control module grounds for being clean, tight, and in their
proper locations. |
| • | Inspect the generator output voltage. Repair if less than 9 volts
or more than 16 volts. |
| • | Inspect the vacuum lines for restrictions, leaks, or improper connections. |
| • | Inspect the torque converter clutch (TCC) operation. |
|
