Rick's Free Auto Repair Advice

Ford diesel no power

My Ford diesel has no power

Owners of Ford 7.3L diesel Direct Injected Turbo (DIT) or PowerStroke engines may have a situation with Ford diesel no power where the engine starts and idles fine but will not accelerate. Ford installed “drive-by-wire” technology in these vehicles. So the accelerator pedal no longer is connected to the engine by a cable. Instead it acts like a throttle position sensor. Ford refers to this sensor as an Accelerator Position Sensors (AP). To act as a redundant sensor, Ford also adds an Idle Validation Switch (IVS).

The IVS receives battery voltage on the red/yellow wire. The switch is OPEN when your foot is off the gas and the engine is idling. To check the operation of this switch, connect your digital voltmeter to the red/yellow wire. It should read battery voltage with your foot off the pedal and switch to less than 0.5 volts as you press down on the pedal.

The AP sensor gets a 5 volt reference signal from the PCM on the brown/white wire. The yellow/white is the ground wire. As you depress the accelerator, the AP changes the voltage going to the PCM on the gray/white wire. It should vary from 0.9 – 4.5 volts (4.5 at full throttle). You must test both switches at the same time to determine correct operation. Connect two meters or a dual trace scope to both sensors. As you depress the pedal, watch the voltage on the AP sensor gray/white wire. When it reads approximately 1.3 volts, the IVS switch should close and you should see battery voltage on the red/light green wire.

If the voltages on the two switches do not synchronize, the PCM will conclude there’s a problem and the vehicle will not accelerate. It will only idle. Replace the accelerator pedal to correct the condition.

 

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat



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