Multec 3.5 Fuel Injector Application Manual Software
Delphi Energy and Chassis Systems
Revision: 11/05-1 5-11
5.2.3.4 Altitude/Barometer Correction
Altitude/barometer correction is used to compensate for changes in air
density at different altitudes.
5.2.3.5 Engine Coolant Temperature (ECT)
The engine coolant temperature signal is used to compensate fueling
during warm-up. Due to the lower fuel vapor formation rates at cooler
temperatures, the ECT signal schedules richer air/fuel ratios to achieve a
combustible mixture in the cylinder. ECT can be used alone or in
conjunction with intake air temperature (IAT).
5.2.3.6 Intake Air Temperature (IAT)
Early systems did not use IAT but relied strictly on ECT. Air density
varies with air temperature (i.e., hot air is less dense than cold air), and air
density changes directly affect the air/fuel ratio. On speed density
systems, intake air temperature is used to determine changes in air density
so injector pulse-widths can be adjusted to achieve the required air/fuel
ratio.
Certain conditions reduce the effectiveness of the ECT in predicting
charge temperature (i.e., when the engine is warm and ambient air
temperature is cold). In these situations, the IAT gives a better indication
of the condition of incoming air temperature.
5.2.3.7 Manifold Absolute Pressure (MAP)
MAP is used to measure air density in speed density fuel systems. Air
density is an indication of air mass going into the cylinder and is used to
adjust fueling.
5.2.3.8 Power Enrichment Mode (PE)
To obtain maximum power, it is necessary to enrich the A/F to a value
rich of stoichiometric. This ensures that all cylinders have sufficient fuel
for maximum power. PE is typically based on TPS and can vary with
rpm, altitude, etc. Rich A/F ratios result in increased emissions; therefore
it is critical to avoid PE during the emissions test schedule.
Final PE A/F ratios may be affected by the need to further enrich the
mixture to reduce exhaust temperatures to protect pistons, exhaust valves,
etc., from damage.
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