Inspection/Test
| Action
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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.
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Preliminary
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| • | Be sure driver understands transmission torque converter clutch,
and A/C compressor operation as explained in the owners manual. Inform customer
how TCC and the A/C clutch operates. |
|
Sensor/System
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| • | Inspect the Heated Oxygen Sensors (HO2S). The Heated Oxygen sensors
should respond quickly to different throttle positions. If not, test 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 PCM will reduce the amount of fuel delivered
to the engine, causing a severe driveability problem. Refer
to
Information Sensors/Switches Description
. |
| • | Inspect 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 and Camshaft Position 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 to power.
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 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
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. |
| • | Test items which can cause an engine to run rich (long term fuel
trim is significantly in the negative range). Refer to Diagnostic Aids
for DTC P0172. |
| • | Test items that can 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
|
| • | 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 J 26792
spark tester. Leave the other end of
the spark plug wire to the coil being tested. |
| 3. | Connect one end of another spark plug wire to the other coil
tower. Connect the other end of the spark plug wire to ground. |
| 4. | Crank the engine while observing the J 26792
spark tester. A crisp blue spark should be observed. |
| 5. | Repeat the above steps for each coil. |
| • | If adequate 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 - 8000 ohms (5K - 8K ohms) | - | 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
600 ohms per foot (1 968 ohms per meter).
| | Important: : Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. Ignition components will arc to ground
when a secondary component is faulty.
|
| - | Ignition System Wiring - Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and inspect for the following: |
| - | 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. |
|
Additional Inspections
|
| • | Inspect exhaust system for possible restriction: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect muffler for heat distress or possible internal failure. |
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