Checks
| Action
|
DEFINITION: Engine
power variation under steady throttle or cruise. Feels like the vehicle speeds
up and slows down with no change in the accelerator pedal.
|
Preliminary
|
| • | Verify that the powertrain control module (PCM) grounds are clean,
tight, and in the correct locations. |
| • | Ensure that the driver understands the transmission torque converter
(TCC) clutch and the A/C compressor operation as explained in the owner's
manual. Inform the customer how the TCC and the A/C clutch operate. |
|
Sensor
and System
|
| • | Inspect the heated oxygen sensor (HO2S 1). The HO2S 1
should respond quickly to different throttle positions. If the sensor does
not respond correctly, inspect the HO2S 1 for the following conditions: |
| - | Any silicon or other contaminants from the fuel, or the use of
an improper RTV sealant. |
| - | Any phosphorus from excessive oil consumption. |
| - | Either material may cover the sensor with a white powdery coating
and result in a high but false signal voltage and a rich exhaust indication.
The powertrain control module (PCM) will then reduce the amount of fuel
delivered to the engine, causing a severe driveability problem. |
| • | Inspect the mass airflow (MAF) sensor connections. Repair or replace
any terminals as necessary. |
| • | Inspect the EGR system for correct operation. |
|
Fuel
System
|
| • | Inspect for a restricted fuel filter. |
| • | Verify that each injector harness is connected to the correct
injector and cylinder according to the firing order. Relocate the injector
harnesses as necessary. |
| • | Inspect the items that may cause an engine to run rich. |
| • | Inspect the items that may cause an engine to run lean. |
|
Ignition
System
| Remove
the spark plugs. Inspect for the following:
An improper spark plug gap will cause a driveability problem. The spark
plug gapping should be done with a wire gauge gap tool. If the spark plugs
are gas or oil fouled, the cause of the fouling must be determined
before replacing the spark plugs.
| • | Inspect for any loose ignition control module (ICM) grounds. |
| • | Inspect the spark plugs for the correct heat range. |
|
Additional
Checks
|
| • | Inspect the vacuum hoses for splits, kinks, and the correct connections
and routing as shown on the Vehicle Emission Control Information label. |
| • | Inspect the exhaust system for a possible restriction. Refer to
Restricted Exhaust
in Engine Exhaust. |
| • | Inspect for any improper harness routing. An engine miss condition
can be caused by electromagnetic interference (EMI) on some engine controls
circuits. Use the scan tool to inspect for any erratic sensor values
or excessive changes in the indicated RPM with little change in the
actual engine RPM. This may indicate EMI is present. If a problem exists,
inspect for an improper routing of the harness near the high voltage
components or the high current components. |
| • | Inspect the charging system. A bad diode in the alternator can
allow A/C noise to enter the electrical system. This may affect the engine
controls system operation. Refer to
Diagnostic Starting Point - Engine Electrical
in Engine Electrical . |
| • | Inspect the transaxle range (TR) switch circuit. Ensure that
the scan tool indicates that the vehicle is in drive with the gear selector
in Drive or Overdrive. |
|
