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EMRSR
EMRSR, Master Certified Service Manager
Category: Ford
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Experience:  20 years with Ford, Master Certified
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2003 Ford Focus: idles rough..the vacuum lines..DPFE..EGR valve

Resolved Question:

2003 Ford Focus 2.0 idles rough. Found small amount of moister when removed the vacuum lines from the DPFE sensor. Could the DPFE sensor be the trouble or the EGR valve? Also idle smooths out when carb cleaner is sprayer while at idle on the intake where the 3 vacuum lines enter - I found 1 leak - repaired but still runs rough.
Submitted: 7 years ago.
Category: Ford
Expert:  EMRSR replied 7 years ago.

Replace the DPFE sensor and hoses, this is a very common concern.

The Exhaust Gas Recirculation (EGR) system controls the Oxides Of Nitrogen (NOx) emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air/fuel charge. The combustion chamber temperature is reduced, lowering NOx emissions.

Differential Pressure Feedback EGR System

The Differential Pressure Feedback EGR system consists of a differential pressure , EGR vacuum regulator solenoid, EGR valve, orifice tube assembly, Powertrain Control Module (PCM) and connecting wires and vacuum hoses. Operation of the system is as follows (Figure 86):

  1. The Differential Pressure Feedback EGR system receives signals from the Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Throttle Position (TP) sensor, Mass Air Flow (MAF) sensor and Crankshaft Position (CKP) sensor to provide information on engine operating conditions to the PCM. The engine must be warm, stable and running at a moderate load and rpm before the EGR system is activated. The PCM deactivates EGR during idle, extended wide open throttle or whenever a failure is detected in an EGR component or EGR required input.
  2. The PCM calculates the desired amount of EGR flow for a given engine condition. If then determines the desired pressure drop across the metering orifice required to achieve that flow and outputs the corresponding signal to the EGR vacuum regulator solenoid.
  3. The EGR vacuum regulator solenoid receives a variable duty cycle signal (0 to 100%). The higher the duty cycle the more vacuum the solenoid diverts to the EGR valve.
  4. The increase in vacuum acting on the EGR valve diaphragm overcomes the valve spring and begins to lift the EGR valve pintle off its seat, causing exhaust gas to flow into the intake manifold.
  5. Exhaust gas flowing through the EGR valve must first pass through the EGR metering orifice. With one side of the orifice exposed to exhaust backpressure and the other to the intake manifold, a pressure drop is created across the orifice whenever there is EGR flow. When the EGR valve closes, there is no longer flow across the metering orifice and pressure on both sides of the orifice is the same. The PCM constantly targets a desired pressure drop across the metering orifice to achieve the desired EGR flow.
  6. The differential pressure feedback EGR sensor measures the actual pressure drop across the metering orifice and relays a proportional voltage signal (0 to 5 volts) to the PCM. The PCM uses this feedback signal to correct for any errors in achieving the desired EGR flow.

Differential Pressure Feedback EGR System Operation


Hardware

Differential Pressure Feedback EGR Sensor

Differential Pressure Feedback EGR Sensor


The differential pressure feedback EGR sensor (Figure 87) is a ceramic, capacitive-type pressure transducer that monitors the differential pressure across a metering orifice located in the orifice tube assembly. The differential pressure feedback sensor receives this signal through two hoses referred to as the downstream pressure hose (REF SIGNAL) and upstream pressure hose (HI SIGNAL). The HI and REF hose connections are marked on the differential pressure feedback EGR sensor housing for identification (note that the HI signal uses a larger diameter hose). The differential pressure feedback EGR sensor outputs a voltage proportional to the pressure drop across the metering orifice and supplies it to the PCM as EGR flow rate feedback.

Tube Mounted Differential Pressure Feedback EGR Sensor

Tube Mounted Differential Pressure Feedback EGR Sensor

Customer: replied 7 years ago.

So is is fairly safe to say this is not a vacuum leak but a problem with the DPFE sensor and is the moister I found in sensor the key along with rough idle

Expert:  EMRSR replied 7 years ago.
For sure, this is the season for these to fail.
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