Checks
| Action
|
DEFINITION: Engine
power variation under steady throttle or cruise. Feels like the vehicle speeds
up and slows down without a change in the accelerator pedal.
|
Preliminary
|
| • | Be sure that the driver understands transmission torque converter
clutch (TCC) , and the A/C compressor operation. If the owner's manual is
unavailable for reference, inform the customer how the TCC, and the
A/C clutch operates. |
|
Sensor/System
|
| • | Test the heated oxygen sensors (HO2S). The HO2S should respond
quickly to different throttle positions. If not, inspect the HO2S for silicon
or other contaminants from fuel, or from use of an incorrect RTV sealant.
The sensors may have a white powdery coating. Silicon contamination
causes a high, but false, HO2S signal voltage. This is a rich-exhaust
indication. The powertrain control module (PCM) will reduce the amount
of fuel delivered to the engine, causing a severe driveability condition. |
| • | Test the mass airflow (MAF) sensor and inspect the related wiring. |
| • | Test the exhaust gas recirculation (EGR) valve for a stuck open
pintle. |
|
Fuel System
|
| • | Test items which can cause an engine to run rich, such as the
long-term fuel trim (FT) is significantly in the negative range. Refer to
Diagnostic Aids for
DTC P0172 or P0175
. |
| • | Test items that can cause an engine to run lean, such as long-term
FT is significantly in the positive range. Refer to Diagnostic Aids for
DTC P0171 or P0174
. |
|
Ignition System
|
| • | Test for proper ignition voltage output using the following steps: |
| 1. | Clip the J 26792
Spark Tester to engine ground. |
| 2. | Connect one end of a spark plug wire to the spark tester. Leave
the other end of the spark plug wire connected to the coil being tested. |
| 3. | Connect another spark plug wire between the remaining tower of
the coil being tested and ground. |
| 4. | Crank the engine while observing the spark tester, a spark should
be observed. |
| 5. | Repeat the above steps for each coil. |
| • | If adequate spark is not present at the coils, test for the following
conditions: |
| - | Coils--Evidence of carbon tracking or arcing, cracks in the
coils, or a resistance value outside the specified range: |
Coil Secondary Resistance
5000-8000 ohms (5K-8K ohms)
| | Important: Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent condition. Ignition components will arc to ground
when a secondary component is malfunctioning.
|
| - | Spark plug wires--Inspect for the following conditions: |
| • | Evidence of cross firing |
| - | Spark plug wires--Inspect for a resistance value more than
the specified value: |
Spark Plug Wires Resistance
3280-4921 ohms/meter (1000-1500 ohms/ft) | - | Malfunctioning ignition control module |
| - | Ignition system wiring--Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| • | If spark plugs are gas or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
|
Additional
Tests
|
| • | Inspect the exhaust system for a possible restriction in the following
components: |
| - | Damaged or collapsed pipes |
| - | Heat distress or possible internal failure in the muffler |
| - | Plugged three-way catalytic converter--Test for possible
plugged conditions. Refer to
Restricted Exhaust
in Engine Exhaust. |
|
