Checks
| 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. |
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Sensor/System
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| • | Check the Heated Oxygen Sensor(s). The Heated Oxygen Sensors should
respond quickly to different throttle positions. If not, check the HO2S for
silicon or other contaminants from fuel or use of incorrect RTV sealant.
The sensors may have a white powdery coating. Silicon contamination causes
a high but false HO2S signal voltage (rich exhaust indication). The PCM
will reduce the amount of fuel delivered to the engine, causing a severe
driveability problem. Refer to Heated Oxygen Sensor(s) in
Information Sensors/Switches Description
. |
| • | Check MAF Sensor and related wiring. |
| • | Check the EGR valve for a stuck open pintle. |
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Fuel
System
|
| • | Check the fuel pressure. |
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Ignition
System
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| • | Check for proper ignition voltage output using the following steps: |
| - | Clip the J 26792
spark tester to engine ground. |
| - | Connect one end of a spark plug wire to the spark tester; leave
the other end of the spark plug wire to the coil being tested. |
| - | Connect one end of another spark plug wire to the other coil tower;
connect the other end of the spark plug wire to ground. |
| - | Crank the engine while observing the spark tester; a spark should
be observed. |
| - | Repeat the above steps for each coil. |
| • | If adequate spark is not present at the coil(s), check for the
following conditions: |
| - | Coil(s) - Cracks, carbon tracking/arcing, or a resistance value
outside the specified range. |
Coil Secondary Resistance
5000 - 8000 ohms (5K - 8K ohms) | - | Spark Plug wires - Signs of arcing/cross firing, cracks, carbon
tracking, plug boot damage, pinched, incorrect routing, or a resistance value
greater than the specified value. |
VIN K Spark Plug Wires Resistance
3280-4921 ohms/meter(1000-1500 ohms/ft).
| | 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 malfunctioning.
|
| - | Malfunctioning ignition control module. |
| - | Ignition System Wiring - Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and check 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. |
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Additional
Checks
|
| • | Check TCC operation. Refer to 4L60-E Automatic Transmission
Diagnosis. |
| • | Check the exhaust system for a possible restriction: |
| - | Inspect the exhaust system for damaged or collapsed pipes. |
| - | Inspect the muffler for heat distress or possible internal failure. |
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