7.3L Power Stroke AIH Operation & Delete Information
The AIH rarely cycles "ON" and is only used when the following conditions are met:
• Transmission is in park (automatic) or neutral (manual).
• Parking brake is set (applies to manual transmissions only).
• Engine oil temperature (EOT) is below 131° F (55° C).
• Engine speed is above 1,000 rpm.
• Intake air temperature (IAT) is below 32° F (0° C) if engine high idle is ~1,000 rpm, IAT below 14° F (-10° C) if engine high idle is ~1,100 rpm.
• System voltage to PCM is between 11.8 and 15.0 volts.
• Glow plugs are deactivated (not currently cycling).
• Brake pedal is NOT depressed.
• Accelerator pedal is in the idle position (not depressed).
The heating element of the AIH is relatively large and consumes a substantial portion of the cross sectional area of the intake tube. The profile of the AIH assembly is approximately 0.98 in2 while the area of the intake plenum just aft of the heater is approximately 5.36 in2. The AIH therefore consumes 18% of the flow area of the intake plenum. However, removing (deleting) the AIH will result in no noticeable nor measurable gains in performance or fuel economy as flow across the device is not significantly impeded. While deleting the AIH technically improves the quality of airflow through the spider intake it is not a substantial improvement and is only likely to impact heavily modified engines that are working at high intake manifold pressures and flowrates; even then, gains are marginal. Common reasons for performing an AIH delete include:
1) The AIH fails/malfunctions and sets off the check engine light. The replacement part (Ford F81Z-9N424-BA) is in the $90 to $120 range while a delete plug and CEL eliminator is in the $30 range.
2) Improved airflow; though marginal, the AIH is considered an intake restriction.
3) The AIH bung is a suitable location to mount a manifold pressure sensor or pressure hose to feed an aftermarket boost gauge.
4) Deleting the AIH is completely and easily reversible, thus removing the heater when the weather is warm and reinstalling it during cooler months may prolong the life of the device (in rare circumstances).
5) The conditions in which the AIH will cycle are never met in your region and thus the AIH is deemed an unnecessary component.
It's worth noting that vehicles operated in cold weather may benefit from AIH cycles as it can aid in reducing wet stacking (fuel dilution) when an engine is running below operating temperature. There is little evidence, however, to suggest that the AIH plays a significant role in reducing the time required for an engine to reach operating temperature. The IAH does not and will not cycle on while the engine is off, the vehicle is moving, or if it has reached normal operating temperature. It is located on the "cold side" of the intake air system, meaning that it is positioned downstream of the intercooler.
Deleting the intake heater is as simple as removing (requires 1 inch socket) and replacing it with a M22x1.50 plug. There are many aftermarket options available, some of which feature a threaded hole for a boost gauge compression fitting. Likewise, the oil pan drain plug from a 5.9L Cummins turbodiesel happens to be the correct thread size and is an inexpensive option for someone wishing to experiment with deleting the air intake heater.
AIH Delete P0541 Code Eliminator
Deleting the AIH may trigger the check engine light and set a P0541 DTC as the PCM will recognize that it is disconnected. Eliminating the DTC is as simple as installing a AIH code eliminator pigtail, which can be built inexpensively using the specifications below:
Remove the AIH feed wire and install one end of the code eliminator in its place on the relay. Secure the remaining end of the code eliminator pigtail to a good ground. When the PCM performs a system scan, it will detect a small current draw from the resistor and infer that it is the heater. Note that the resistor should be protected with 1 or more layers of heat shrink tubing.