Winnebago 1987-1989 LeSharo Service Manual page 145

ENGINE FUEL SYSTEM
INTEGRATOR VOLTAGE
IMPORTANT
Do not overlook the charcoal canister or fuel
pressure when diagnosing an over-rich condition.
The most common problem with a lean mixture is
vacuum leaks. These can be traced by pinching off
various vacuum hoses while observing the effect
on integrator voltage.
Pinching off the lines works well in a rich
condition to isolate a bad cold start injector or a
saturated charcoal canister.
IMPORTANT
One cylinder not firing ("Missing"):
NOTE: When diagnosing a possible injection
problem be sure that the engine is
running on all four cylinders. Also, be sure
that there is fuel, air and ignition to all
cylinders.
An ignition malfunction may seem like an
over-rich condition, but integrator voltage
indicates a lean condition. However, an ignition
oscilloscope will reveal an ignition miss, which
results in unburned fuel/air mixture being
dumped into the exhaust manifold.
The
O2
sensor detects the higher oxygen content
of the unburned mixture and passes this
information on to the ECU. (Remember: The
O2
sensor detects oxygen content only - it cannot
detect unburned fuel.)
Since the ECU is incapable of determining that a
cylinder is not firing, it will try to compensate for
the higher oxygen content in the exhaust by
further enriching the fuel/air mixture. This causes
an abnormal running condition, which results in
high integrator voltage and misfiring of the
remaining cylinders.
NOTE: A disconnected or inoperative fuel
injector will also produce similar
symptoms.
When diagnosing a fuel injection system, be very
careful not to overlook ignition problems or
restricted air intake or exhaust systems.
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