Checks
| 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,
and A/C compressor operation as explained in the owners manual. Inform customer
how TCC and the A/C clutch operates. |
|
Sensor/System
|
| • | 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). The PCM
will reduce the amount of fuel delivered to the engine, causing a severe
driveability problem. Refer to
Information Sensors/Switches Description
- Heated Oxygen Sensor(s). |
| • | Check MAF Sensor and related wiring. |
|
Fuel System
|
| • | 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 Fuel Trim System Rich
. |
| • | 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 Fuel Trim System Lean
. |
|
Ignition System
|
| • | 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 plugs(s), check for the following
conditions: |
| - | Inspect the coil(s) for cracks, carbon tracking/arcing, or a secondary
resistance value outside the specified range. |
Coil Resistance
5000 - 8000 ohms (5K - 8K ohms) | - | Inspect the spark plug wires for 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 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.
|
| - | Inspect for a malfunctioning ignition control module. |
| - | Inspect the ignition system wiring for loose ignition module feed
or ground connection, or damaged system wiring. |
| • | Remove spark plugs and check for the following: |
| | Important:: If carbon tracking is detected on any component, replace that component
and it's mate.
|
| - | Carbon tracking on the porcelain and pitting on the plug wire contact |
| - | 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. |
| • | Check for the following intermittent ignition system conditions: |
| - | CKP Sync or CKP 18X Signal. |
| - | Ignition Feed circuit or sensor ground circuit to the crankshaft
position sensor or camshaft position sensor. |
| - | camshaft position signal, |
|
Additional Checks
|
| • | Check exhaust system for possible restriction: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect muffler for heat distress or possible internal failure. |
| - | Check for possible plugged Three-Way catalytic converter by checking
exhaust system back pressure. |
|
