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 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
Information Sensors/Switches Description
. |
| • | Check MAF Sensor and related wiring. |
| • | Check the EGR system for proper operation. |
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Fuel System
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| • | Ensure each injector harness is connected to the correct injector/cylinder. |
| • | Check 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. |
| • | Check 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. |
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Ignition System
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| • | Check for proper ignition voltage output using the following steps: |
| - | Clip the spark tester J 26792 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 spark is not present at the plug, check for the following
conditions: |
| - | Coil(s)--Cracks, carbon tracking/arcing, or a secondary resistance
value outside the specified range. |
Coil Secondary Resistance
5000-7000ohms (5K-7Kohms) | - | 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 components will arc to ground
when a secondary component is faulty.
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| - | Check for a malfunctioning ignition control module. |
| - | Check the ignition System Wiring--Loose ignition module
feed or ground connection, or damaged system wiring. |
| • | Remove spark plugs and check for the following condition: |
| - | 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. |
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Additional Checks
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| • | Check 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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