Inspection/Test
| Action
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DEFINITION: Momentary lack of response as the accelerator is pushed down. Can
occur at any vehicle speed. Usually more pronounced when first trying to make the
vehicle move, as from a stop sign. May cause the engine to stall if severe enough.
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Preliminary
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Sensor/System
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| • | 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. The powertrain control module (PCM) reduces the
amount of fuel delivered to the engine, causing a severe driveability condition. |
| • | 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 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 they 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. |
| • | Inspect the throttle position (TP) sensor and related wiring. |
| • | Inspect the 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. |
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Fuel System
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| • | 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 which may 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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| • | 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
5,000-8,000 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
9,868 ohms per
meter (3,000 ohms per foot)
| | Important: : Spraying the secondary ignition wires
with a light mist of water may help locate an intermittent condition. Ignition voltage
arcs 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
. |
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