Checks
| Action
|
DEFINITION: Steady
pulsation or jerking that follows engine speed, usually more pronounced as
engine load increases.
|
Preliminary
|
• | Search for service bulletins. |
• | Connect a scan tool and look at the misfire data to possibly isolate
a specific cylinder fault. |
|
Fuel
System
|
• | Check the fuel filter for a plugged or restricted condition. |
• | Check items which can cause an engine to run rich--Long Term
FT 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
FT significantly in the positive range. Refer to Diagnostic Aids for
DTC P0171 Fuel Trim System Lean
. |
• | Check for proper operation of the evaporative emission (EVAP)
control system. |
|
Sensor/System
|
• | Check the oxygen sensor (O2S 1). The O2S 1 should
respond quickly to different throttle positions. If not, check the O2S 1
for silicon or other contaminants from fuel or the use of improper
RTV sealant. The sensors may have a white powdery coating. Silicon
contamination causes a high but false O2S 1 signal voltage--rich
exhaust indication. The powertrain control module (PCM) will reduce
the amount of fuel delivered to the engine, causing a severe driveability
problem. |
• | Check for proper operation of the TP sensor. |
• | Check for proper operation of the ECT sensor. |
• | Check for proper operation of the CKP sensor. |
• | Check for proper operation of the CMP sensor. |
|
Ignition
System
|
• | Check for proper ignition voltage output with the J 26792
spark tester. |
• | Check the spark plugs for the following conditions: |
- | Cracks on the spark plugs |
- | Improper spark plug gap |
- | Burned electrodes or heavy deposits |
• | If the spark plugs are fuel or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
• | Check the ignition control module (ICM) for proper ground connection. |
• | Check the ignition coils for cracks or carbon tracking. |
• | Check the spark plug wires for proper resistance and condition. |
|
Engine
Mechanical
|
• | Check engine mechanical for the following: |
- | Sticking or leaking valves |
- | Excessive oil in combustion chamber and leaking valve seals |
- | Low cylinder compression |
• | Inspect the following components for incorrect basic engine parts: |
• | Refer to the appropriate diagnostic procedures in Engine Mechanical. |
|
Additional
Checks
|
• | Check the following components of the exhaust system for possible
restrictions: |
- | Inspect exhaust system for damaged or collapsed pipes. |
- | Inspect mufflers for heat distress or possible internal failure. |
• | An engine miss condition can be caused by electromagnetic interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
engine RPM with a scan tool. A sudden increase in RPM with little
change in actual engine RPM change, indicates EMI is present. If
a condition exists, check routing of secondary ignition wires high voltage
components--near ignition control circuits. |
• | Check for malfunctioning motor mounts. |
|