Inspection/Test
| 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
|
| • | Make sure that the driver understands the transmission torque converter
clutch (TCC), and the A/C compressor operation as explained in the owners manual.
Inform the customer how TCC and the A/C clutch operates. |
|
Sensor/System
|
| • | Monitor the heated oxygen sensors (HO2S). The heated oxygen sensors should
respond quickly to different throttle positions. If not, inspect the HO2S for silicon
or other contaminants from fuel or use of improper RTV sealant. The sensors may
have a white powdery coating. Silicon contamination causes a high but false HO2S
signal voltage, rich exhaust indication. Refer to
Notice: Contamination of the oxygen sensor can result from the use of an inappropriate
RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption.
Remove the HO2S and visually inspect the portion of the sensor exposed to
the exhaust stream in order to check for contamination. If contaminated, the
portion of the sensor exposed to the exhaust stream will have a white powdery
coating. Silicon contamination causes a high but false HO2S signal voltage
(rich exhaust indication). The control module will then reduce the amount
of fuel delivered to the engine, causing a severe driveability problem. Eliminate
the source of contamination before replacing the oxygen sensor.
. The powertrain control
module (PCM) will reduce the amount of fuel delivered to the engine, causing a severe
driveability condition. |
| • | Inspect mass air filter (MAF) sensor and related wiring. |
| • | Inspect the air intake ducts for being collapsed, damaged areas, looseness,
improper installation, or leaking especially between the MAF sensor and the throttle
body. |
| • | Monitor the 24X crank sensor and the CMP sensor signal present parameters
on the scan tool. If both are not responding, test the sensor feed circuit. Both
sensors use a separate feed circuit but are internally connected to power. Test
all CKP sensor A and CMP sensor circuits for intermittents. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring
Systems. |
| • | Monitor the 3X crank sensor parameter on the scan tool. If the 3X crank
sensor parameter is not responding, inspect the CKP sensor B and circuits
for intermittents. Inspect the ignition control (IC) circuit, IC timing control circuit,
low resolution engine speed signal circuit and the low reference circuit for intermittents.
If these circuits become open, or shorted may not set a DTC immediately, but are
capable of causing driveability complaints. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
|
Fuel System
|
| • | Make sure that each injector harness is connected to the correct injector/cylinder. |
| • | Inspect any items which may cause an engine to run rich, long term fuel
trim is significantly in the negative range. Refer to Diagnostic Aids for DTC P0172. |
| • | Inspect any items that may cause an engine to run lean, long term fuel
trim is significantly in the positive range. Refer to Diagnostic Aids for DTC P0171. |
|
Ignition System
|
| • | Inspect for proper ignition voltage output using the following steps: |
| 1. | Attach the J 26792
Spark Tester to engine ground. |
| 2. | Connect the spark plug end of the spark plug wire to the J 26792
. Connect the other end of the spark plug wire
to the coil being tested. |
| 3. | Connect the spark plug end of the companion spark plug wire to ground.
The companion spark plug wire is the wire attached to the corresponding coil tower. |
| 4. | Crank the engine while observing the J 26792
. A spark should be observed. |
| 5. | Repeat the above steps for each coil. |
| • | If spark is not present at the coils, inspect for the following conditions: |
| - | Coils--Cracks, carbon tracking/arcing, or a resistance value outside
the specified range. |
Coil Resistance
5000-8000ohms (5K-8Kohms) | - | Spark Plug wires--signs of arcing, cross firing, cracks, carbon
tracking, plug boot damage, pinched, improper routing, or a resistance value outside
the specified range. |
Spark Plug Wire Resistance
9868ohms per meter (3000ohms per foot)
| | Important: : Spraying the secondary ignition wires with a light mist of water may help locate
an intermittent condition. Ignition voltage will arc to ground when a secondary
component is faulty.
|
| - | Defective ignition 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 |
| - | Improper heat range or reach |
| • | If spark plugs are gas or oil fouled, the cause of the fouling must be
determined before replacing the spark plugs. Refer to
Spark Plug Inspection
. |
|
Additional
|
| • | Inspect the exhaust system for possible restriction: |
| - | Inspect the exhaust system for damaged or collapsed pipes. |
| - | Inspect the muffler for heat distress or possible internal failure. |
| - | Test for possible catalytic converter restrictions by testing the exhaust
system back pressure. |
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