Surges/Chuggles

SYMPTOM DESCRIPTION:
Engine power variation, under steady throttle or cruise. Feels like the vehicle speeds up and slows down, with no change in the accelerator pedal.




SYSTEM OR COMPONENT TO CHECK ACTION

COMPUTER INPUTS/OUTPUTS CHECK: ^ OXYGEN SENSOR (O2) - Inspect sensor for
silicon contamination from fuel, or use of
improper RTV sealant.
The sensor will have a white, powdery coating,
and will result in a high but false signal
voltage (rich exhaust indication). The ECM/BCM
will then reduce the amount of fuel delivered
to the engine, causing a severe driveability
problem.
^ ECM grounds for being clean,
tight, and in their proper location.
NOTE: ^ Use the "Diagnostic Mode" to make sure reading
of VSS matches vehicle speedometer except
vehicles with 4L80-E transmission where some
variation between VSS and speedometer is normal. See "Note On
Intermittents" in DIAGNOSTIC CHARTS
/TROUBLE CODE CHARTS/CODE E24 OR EO24




FUEL NOTE: To determine if the condition is caused by
a lean system, the vehicle should be driven at the
speed of the complaint. If closed loop is achieved,
the fuel system has to checked for rich, lean or
improper fuel control. The DFI system has ECM
parameter ED19 "Integrator" which monitors the
oxygen sensor rich lean status and drives the fuel
system richer if the 02 sensor is lean or
leaner if the sensor is rich.
To help identify the problem
Refer to DFI SYSTEM CHECK. Or codes E44, EO44
for lean conditions and E45, EO45 for rich
NOTES ON INTERMITTENTS.
CHECK: ^ FUEL PRESSURE: use CHART A-4A in
DIAGNOSTIC CHARTS/A-CHARTS
^ FUEL INJECTOR BALANCE TEST.
^ IN-LINE FUEL FILTER.




IGNITION CHECK: ^ Proper ignition voltage output with
spark tester J26792 or equivalent (ST-125).
^ Spark plugs, wet plugs, cracks, wear, improper
gap, burned electrodes or heavy deposits.
^ IGNITION TIMING.




EMISSIONS CHECK: ^ EGR SYSTEM.
NOTE: ^ Refer to EMISSION CONTROLS
for complete testing procedures.





ENGINE CHECK: ^ Vacuum lines for kinks and leaks.
^ Generator output voltage. Repair if less than
9 or more than 16 volts.
^ VCC operation.
NOTE: ^ Be sure driver understands
Viscous Converter Clutch (VCC) and A/C
compressor operation in owner's manual.