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
|
| • | Refer to Symptoms, Important Preliminary Checks Before Starting. |
| • | Verify that the PCM grounds are clean, tight, and in the correct
locations. |
| • | Be sure 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
|
| • | Check the heated oxygen sensor (HO2S 1). The HO2S 1
should respond quickly to different throttle positions. If the sensor does
not respond correctly, check 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 PCM will then reduce the amount of fuel delivered to the engine,
causing a severe driveability problem. |
| • | Check the MAF sensor connections. Repair or replace any terminals
as necessary. |
| • | Check the EGR system for correct operation. |
|
Fuel
System
|
| • | Check 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. |
| • | Check the items that may cause an engine to run rich. |
| • | Check the items that may cause an engine to run lean. |
|
Ignition System
| Remove the spark plugs and check 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.
| • | Check for any loose ignition control module grounds. |
| • | Check the spark plugs for the correct heat range. |
|
Additional Checks
|
| • | Visually and physically check the vacuum hoses for splits, kinks,
and the correct connections and routing as shown on the Vehicle Emission Control
Information label. |
| • | Check the exhaust system for a possible restriction. Refer to
Restricted Exhaust
in Engine Exhaust. |
| • | Check 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 check 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, check
for an improper routing of the harness near the high voltage components
or the high current components. |
| • | Check 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 . |
| • | Check the transaxle range switch circuit and ensure the scan tool
indicates that the vehicle is in drive with the gear selector in Drive or
Overdrive. |
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