| 1. |
Duplicate drivability concern and document,
when they occur, how frequently they occur, as well as other details
that may provide information as to cause of concern. |
| 2. |
Perform following basic inspections: |
| |
a. |
Verify adequate cranking and engine
running battery voltage. |
| |
b. |
Inspect air filter for excessive dirt
or contamination, clean as required. |
| |
c. |
Inspect and adjust idle speed, as required. |
| |
d. |
Confirm base timing is properly set
to specifications. |
| |
e. |
Confirm that fuel pressure is within
proper range. |
| |
f. |
Perform inspection of engine mechanical
condition. |
| |
g. |
Perform visual inspection of accessible
electrical connections, vacuum and air induction ducting. |
| |
h. |
Locate and inspect condition of ECM/PCM
main grounds. |
| |
i. |
Inspect for leakage in EGR and PCV
valves. |
| |
j. |
Inspect for unwanted fuel entering
intake manifold from EVAP system, fuel pressure regulator diaphragm,
or crankcase ventilation system. |
| 3. |
Connect a suitably programmed scan
tool and perform OBDII diagnostic test functions. |
| 4. |
Retrieve and record diagnostic trouble
codes (DTC's). Follow appropriate DTC chart for codes retrieved. |
| 5. |
Verify engine speed, coolant temperature,
load, throttle position, intake air temperature, and oxygen sensor
signals are within normal range. |
| 6. |
Verify feedback system is maintaining
normal closed loop control. |
| 7. |
Common vehicle performance concerns
and causes are as follows: |
| |
a. |
Bucking: This term describes a severe,
back and forth jerking motion of vehicle shortly after acceleration
or deceleration. Severity of this symptom is much greater than that
of a surge, to point of which it physically jerks vehicle back and
forth. If bucking condition is severe, movement of vehicle may cause
drivers foot to jerk up and down on accelerator pedal further exaggerating
condition. Common causes of bucking include fluctuating air/fuel
mixture, improper ignition/spark advance system operation and excessively
sensitive accelerator pedal linkage. |
| |
b. |
Poor acceleration: Poor acceleration
is a general term used to describe any acceleration condition that
is slower than expected. This symptom can originate from many different
causes. Most of causes of poor acceleration result from either mechanical
or engine related concerns. Common causes of poor acceleration include
excessively lean or rich air/fuel mixture, restricted intake air
system, incorrect ignition timing advance, restricted exhaust system,
improper torque converter operation and dragging brakes. |
| |
c. |
Hard Starting: Hard starting is a term
used to describe an engine that requires an excessive amount of
time to start, repeated cranking attempts, or starts but stalls
shortly thereafter. Some of more common causes include: excessively
lean air/fuel mixture during cold start-up, low battery voltage,
poor starter performance, ignition system problems, restricted intake
air system, excessively high engine oil viscosity and excessively
rich air/fuel mixture. |
| |
d. |
Rough Idle: Rough Idle describes an
engine idle characteristic that is unexpectedly harsh or unstable.
An excessively rough idle can even cause engine to stall. Common
causes of rough idle include: low engine idle speed, excessively
lean or rich air/fuel mixture, improper ignition system operation
and improper EGR system operation. |
| |
e. |
Engine Stall: Engine stall describes
a condition where engine unexpectedly stops while running. Engine
stall can occur at any time; however, it is most commonly described
as a condition where engine dies just after startup, completion
of fast idle, decelerating to idle, or shifting. Some of more common
causes include: Excessively low idle speed adjustment, excessively
lean or rich air/fuel mixture, intermittent ignition system operation,
and improper air bypass operation. |
|
Oil Pump, Replace
Precautions