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Frequently Asked Questions
What is the difference between closed loop mode and open loop mode?
In
Open Loop mode
, an oxygen sensor may be used for monitoring air/fuel
ratio information. However, in open loop mode, if the measured air/fuel ratio
deviates from the targeted air/fuel ratio, no corrections are made to the
amount of fuel being injected.
In
Closed Loop mode
, an oxygen sensor may be used for monitoring
purposes as well. However, in closed loop mode, if the measured air/fuel
ratio deviates from the targeted air/fuel ratio, the fuel injection system will
automatically increase or decrease fuel delivery to align the measured air/fuel
ratio with the targeted air/fuel ratio.
Why do I sometimes get very lean air/fuel ratio readings even if the car is
obviously running very rich?
In many cases, this is due to exhaust reversion. Exhaust reversion is
common in high performance applications where large camshafts and large
diameter exhaust systems are used. At low engine speeds, particularly at
idle, the airflow in the exhaust stream repeatedly changes direction. This can
actually pull outside air into the exhaust system, causing the oxygen sensor
to register a falsely lean condition. Open header exhaust systems are the
most prone to this. If this happens in your application, it is advisable to
disable closed loop correction at low engine speeds. As the engine speed and
load increases, the amount of reversion in the exhaust system will decrease.
Exhaust reversion has little or no impact on oxygen sensor readings at wide-
open throttle. If you obtain normal air/fuel ratio readings at WOT but not at
idle or cruise, this is the likely culprit.
Air leaks in the exhaust system can cause false lean readings. Outside air is
drawn into the exhaust stream through leaks in gaskets, welds, slip joints,
rust holes, or cracks. If you have any exhaust system leaks, they must be
sealed to ensure proper operation of the oxygen sensor.
Inspect the sensor for any obvious physical damage. You can check the
sensor for a broken heating element by holding the sealing washer in place
and shaking the sensor. Much like a light bulb, the element will rattle inside
the unit if it is broken.
If the sensor appears to be heavily coated in carbon or oil, it may have failed
due to contamination. Contact your Accel DFI Engine Management
Installation Center (EMIC) for further information on troubleshooting or
replacing the sensor.
Is this system compatible with leaded gasoline?
This system is compatible with leaded gasoline. Oxygen sensor
manufacturers state that the presence of lead in the fuel system will
substantially reduce the life expectancy of an oxygen sensor. However, there
are many racers who have received several years of service from a single
oxygen sensor.
