Software Multec 3.5 Fuel Injector Application Manual
5-14
Delphi Energy and Chassis Systems
Revision: 11/05-1
Top Speed Limiters
Top speed limiters shut off the fuel when the vehicle goes above a
predetermined speed (MPH or KPH).
Fail Soft (Limp Home)
If a sensor fails, the vehicle will still operate by using the remaining
sensors to predict the failed sensor’s reading. However, driveability and
emissions may be affected. As an example, if the mass air flow sensor
fails, the system could switch to speed density operation.
Fuel Pump Correction
A decrease in fuel pressure causes a decrease in the flow from the
injectors. As system voltage decreases, such as during a crank condition,
voltage to the fuel pump is also reduced, resulting in reduced fuel flow
and pressure to the injectors. A correction factor increases the pulse-width
proportionally to compensate for the reduction in fuel pressure.
5.2.4 Closed-Loop Corrections
Oxygen sensors are located in the exhaust system and must be heated to
200 – 300°C (392 - 572°F) before they become active. Also, the catalytic
converter’s ability to remove hydrocarbons, carbon monoxide and oxides
of nitrogen is reduced until the converter reaches operating temperature.
Seventy percent or more of the total vehicle emissions during an EPA test
cycle are generated before the catalytic converter reaches operating
temperature. To reduce time to activity and improve emissions, some O
2
sensors are electrically heated internally. Also, spark timing can be
retarded to help raise exhaust temperature and assist the O
2
sensor and
catalytic converter in warming up.
Closed-loop systems use feedback from the oxygen sensors to maintain
the correct air/fuel ratio. Most automotive oxygen sensors are made of
zirconia. This ceramic material will produce a voltage in response to the
amount of unused oxygen in the exhaust stream. It does this by
comparing the amount of oxygen in the exhaust to the amount of oxygen
in the air. When the exhaust is lean (excess air), the sensor produces a
low voltage (near zero volts). When the exhaust is rich (excess fuel), it
produces a high voltage (up to one volt). V6 and V8 engines with a split
exhaust system may have separate oxygen sensors for each bank. Under
these conditions, the air/fuel ratios for each bank are controlled separately.
Closed-Loop Correction is a system for fast correction of air/fuel ratio
variations. Proportional correction
is a calibrated step change in BPW
(faster) each time a rich or lean error occurs. The size of the correction is
intended to toggle the oxygen sensor between rich and lean conditions
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