Differential pressure regulator controls fuel flow in lower chamber of fuel distributor. This helps to determine fuel mixture. Regulator designates zero Milliamps (mA) as reference point. With vehicle at normal operating temperature and all engine controls functioning properly, regulator operates with current from FICU between +10 mA (rich) to -10 mA (lean) ranges.

When starter is operated, current to differential pressure regulator is increased to enrich fuel mixture. This will take place whenever engine is started and amount of increase will be regulated by coolant temperature. In extreme cold, current can be as high as 140 mA. During cold acceleration, current can briefly raise to 6 mA to enrich fuel mixture. Enrichment is determined by engine speed and signals from temperature sensor.

During full load operation, full throttle switch closes, sending a signal to ICU. ICU sends a signal approximately 3 mA greater than signal that is currently present. This signal will vary, depending on engine speed and altitude.

When vehicle is decelerated, fuel to injectors is shut off by reversing current to -50 mA to -60 mA. Engine speed at which this reversing will take place is regulated by coolant temperature. Current will also be reversed if engine speed reaches 6600 RPM, acting as a governor. Differential pressure regulator is attached to fuel distributor. See Figure .

Fig 1: Operation of Differential Pressure Regulator

Courtesy of AUDI OF AMERICA, INC.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Differential Pressure Regulator

Use the Manual With the Right Hardware

When to See a Mechanic