GENERAL SYSTEM DIAGNOSTICS SERVICE MANUAL NUMBER 23
Page 5E-2 90-861326--1 MARCH 1999
Diagnostic Circuit Check
The Diagnostic Circuit Check is an organized approach to identifying a problem created by
an electronic engine control system malfunction. It must be the starting point for any drive-
ability complaint diagnosis because it directs the service technician to the next logical step
in diagnosing the complaint.
NOTE: A scan tool that displays faulty data should not be used, and the problem should be
reported to the manufacturer. The use of a faulty scan tool can result in misdiagnosis and
unnecessary parts replacement.
The scan tool data listed in the table may be used for comparison. After completing the diag-
nostic circuit check and finding the on-board diagnostics functioning properly and no trouble
codes displayed. The “Typical Data Values” are an average of display values recorded from
normally operating vessels and are intended to represent what a normally functioning sys-
tem would typically display.
Only the parameters listed below are used in this manual for diagnosing. If a scan reads
other parameters, the values are not recommended for use in diagnosing. If all values are
within the range illustrated, refer to “Troubleshooting.”
Scan Tool Normal Specifications (Idle / Warm Engine / Closed Throttle /
Neutral)
SCAN POSITION UNITS DISPLAYED TYPICAL DATA VALUE
RPM RPM 600-700 RPM
Desired RPM RPM 600 RPM
Coolant Temp. ° F(° C) 150-170° F (66-77° C)
Manifold Air Temp. ° F (° C)
Varies with Ambient Tempera-
ture
Throttle Position Volts .4 to .8 Volts
Throttle Angle 0-100 % 0-1%
MAP Volts or kPa
1-3 Volts or (45-55 kPa)
(Depends on Vacuum and
Baro Pressure)
Baro Volts or kPa
3-5 Volts (Depends on Altitude
and Barometric Pressure)
Bat Volts 12.0-14.5 Volts
Spark Advance Degrees -10 to 30°
Knock Retard Degrees 0°
Idle Air Control IAC Counts (Steps) 0-40 Counts
Minimum IAC Position Counts (Steps) 0-40 Counts
Idle Air Control Follower Counts (Steps) 0 Counts
Injector Pulse Width msec. 2-3 msec.
Injector On Time Cranking msec.
2.5-3.5 msec. (Depends on
Water/Air Temperature)
Fuel Consumption GPH (L/h) 1-2 GPH(3.7-7.5 L/h)
Time From Start 0:00:00-1092:00 Varies
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