Briggs & Stratton BIG BLOCK EFI, Repair Manual

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90 Section 4: Symptoms
Introduction
Verify Customer Complaint
Verify customer complaint and then move to
the Diagnostic Table that best describes the
problem.
• Engine does not crank.
• Engine cranks but does not start.
• Engine exhibits hard start symptoms.
• Engine power output low.
• Engine hunts and surges.
Perform Visual Check
Each Diagnostic Table contains an instruction
to perform a careful visual check. This check
should always include the following:
• Verify that ECM grounds and sensor con-
nections are clean, tight and in their proper
location.
• Thoroughly check for any type of vacuum
leak or restriction.
• Look for air leaks at the throttle body
mounting and intake manifold sealing sur-
faces.
• Inspect ignition wires for cracks, hardness,
improper routing and carbon tracking.
• Inspect wires for kinks, cuts, burns, abrad-
ed insulation, and other damage.
• Look for moisture in primary or secondary
ignition circuit connections.
• Look for salt corrosion on electrical connec-
tions and exposed throttle body linkages.
Check electrical connectors for the following:
• Poor mating of connector halves, or a ter-
minal not fully seated in the connector body
(backed out or loose).
• Improperly formed or damaged terminals
and/or connectors.
• Improper contact tension of connector pin
and socket terminals in the problem circuit.
• Poor terminal to wire connection (both core
and insulation crimps).
Intermittents
IMPORTANT: Intermittents may not cause the
MIL to illuminate or set a DTC. DO NOT use
the DTC Tables to diagnose intermittent prob-
lems. The fault condition must be present to lo-
cate the problem. Many intermittent problems
are caused by faulty electrical connections or
wiring.
The engine may be operated with a DVOM
connected to the suspect circuit. If an abnor-
mal voltage is observed when a malfunction
occurs, it is a good indication that there is a
fault in the circuit. A scan tool also may be
used to help detect intermittents.
Check DTC Memory Loss
Disconnect MAP sensor and idle engine until
MIL is illuminated. DTC P0107 should be set
and stored in ECM memory when the igni-
tion is turned OFF. If it is not, then the ECM
is faulty. After performing this test, be sure to
clear the DTC from memory.
An intermittent MIL with no stored DTC may be
caused by one or more of the following condi-
tions:
• Ignition coil is shorted to ground and arcing
is present at ignition wires or plugs.
• MIL wire to ECM is shorted to ground.
• Poor ECM grounds.
• An electrical system interference caused
by a sharp electrical surge. The problem
normally occurs when the faulty component
is operated.
• Secondary ignition components are shorted
to ground, or there is an open in the ignition
coil ground.
• Engine components, such as starters,
alternators or relays, are internally shorted
to ground.