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
|
| • | Be sure driver understands transmission torque converter clutch
(TCC), and A/C compressor operation as explained in the owners manual. Inform
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 room temperature vulcanizing (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 problem. |
| • | Inspect mass air flow (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 crankshaft position (CKP) and camshaft position
(CMP) sensors on scan tool. If both are not responding, test the sensor feed
circuit. Both sensors use a separate feed circuit but are internally
connected within the PCM. Test all 24X and CMP sensor circuits for intermittents.
Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Monitor the 3X parameter on the scan tool. If the 3X is not responding,
inspect the 7X CKP sensor and circuits for intermittents. Inspect the ignition
control (IC) circuit, bypass circuit, 3X reference high circuit, and
the 3X reference low circuit for intermittents. If these circuits become
open, or shorted may not set a diagnostic trouble code (DTC) immediately,
but are capable of causing driveability complaints. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
|
Fuel System
|
| • | Ensure 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
. Leave the other end of
the spark plug wire connected 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
600ohms per foot (1 968ohms per meter)
| | Important: : Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. 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 exhaust system for damaged or collapsed pipes. |
| - | Inspect muffler for heat distress or possible internal failure. |
| - | Test for possible plugged catalytic converter by testing the
exhaust system back pressure. |
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