Cuts Out, Misses
Tests/Inspections
| Action
|
DEFINITION:
Steady pulsation or jerking that follows engine speed, usually more pronounced
as engine load increases.
|
Preliminary
|
| • | Search for service bulletins. |
|
Fuel System
|
| • | Check for a restricted fuel filter. |
| • | Inspect the items which can cause an engine to run rich (long
term fuel trim significantly in the negative range). Refer to Diagnostic
Aids for
DTC P0172
. |
| • | Inspect the items that can cause an engine to run lean (long term
fuel trim significantly in the positive range). Refer to Diagnostic Aids
for
DTC P0171
. |
| • | Inspect for fuel in the fuel pressure regulator vacuum hose. |
|
Sensor/System
|
| • | Test the oxygen sensor (O2S 1). The O2S 1 should
respond quickly to different throttle positions. If not, inspect the O2S 1
for silicon or other contaminants from fuel or the use of
improper RTV sealant. The sensor may have a white powdery
coating. Silicon contamination causes a high but false O2S
1 signal voltage (rich exhaust indication). The PCM will reduce
the amount of fuel delivered to the engine, causing a severe
driveability problem. |
| • | Test for correct operation of the manifold absolute pressure (MAP)
sensor. |
| • | Test for the correct operation of the throttle position (TP) sensor. |
| • | Test for the correct operation of the engine coolant temperature
(ECT) sensor. |
|
Ignition System
|
| • | Test for the correct ignition voltage output with the J 36012-A
spark plug jumper wires and J 26792
spark tester or equivalent. |
| • | Inspect the spark plugs for the following conditions: |
| - | Any wet or fuel fouled plugs |
| - | Any burnt 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. |
| • | Inspect the ignition control module (ICM) for a correct ground
connection. |
| • | Inspect the ignition coils and the housing for cracks or carbon
tracking. |
|
Engine Mechanical
|
| • | Inspect for the following conditions: |
| - | Any sticking or leaking valves |
| - | Any worn camshaft lobes |
| - | An incorrect valve timing |
| - | Any broken valve springs |
| - | Any excessive oil in a combustion chamber and leaking valve seals |
| - | The correct oil viscosity |
| • | Any incorrect basic engine parts. Inspect the following: |
|
Additional
|
| • | Inspect the exhaust system for the following conditions: |
| - | Any damaged or collapsed pipes |
| - | Any heat distress or internal failure of the muffler |
| • | An engine miss condition can be caused by electromagnetic interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
the engine RPM with a scan tool. A sudden increase in RPM
with little change in the actual engine RPM change indicates
EMI is present. If a problem exists, inspect the routing of secondary
ignition wires near high voltage components. |
| • | Inspect the intake manifold and the exhaust manifold passages
for casting flash. Refer to
Symptoms - Engine Mechanical
in Engine Mechanical . |
| • | An intermittent may be caused by the following conditions: |
| - | Any faulty connections. |
| - | A rubbed through wire insulation. |
| - | A broken wire inside the insulation. |
| • | Inspect the circuitry that is suspected of causing an intermittent
complaint for the following conditions: |
| - | Any backed out terminals. |
| - | Any incorrect mating of terminals. |
| - | Any incorrectly formed or damaged terminals. |
| - | Any faulty terminal-to-wiring connections. |
| - | Any physical damage to the wiring harness. |
|
