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'04 4.0 SOHC EGR Diagram


mjonesjr

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Does anyone have a diagram for the EGR setup on the '04 4.0? I'm trying to see if someone tried to bypass the EGR on my '04 I just bought.

I keep getting a P0401 but the elbow going into the intake is fine and the DPFE looks new.

Thanks in advance.
 


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P0401 is almost always the DPFE starting to fail, looks can be deceiving.

Here is how the EGR system works so you can eliminate other possibilities before replacing the DPFE.
There are 3 parts for the EGR system, not counting the computer(PCM)
1. EGR valve and tube, this valve is opened by applying vacuum to its port
2. EGR modulator(solenoid or activator), it is a 12volt vacuum valve, it passes vacuum to the EGR valve, PCM controls this by sending it 12volts, it is often a pulsed 12volts, not simply an on/off, this allows PCM to open the EGR valve a little or alot.
3. DPFE sensor measures the pressure difference in the exhaust manifold, it has 2 hoses, one is near or on the EGR tube, the other is on the exhaust manifold.
When PCM opens the EGR valve the pressure in the hose on/near the EGR valve/tube will drop, how much it drops tells PCM now far open the valve is, so how much exhaust gas is being added to intake.

P0401: Insufficient EGR Flow Detected
This code comes from the DPFE sensor telling the PCM that there is no or little pressure change after PCM has started to open EGR valve.

It could be the EGR valve is not opening, so leaky vacuum hose back to EGR modulator or valve is broken.
Get a 3ft piece of vacuum hose that will fit EGR Valve port, install it on the EGR valve, start engine, suck on the end of the hose, create a vacuum, EGR valve should start to open and engine should start to run rough and even die, EGR valve is working.
Follow the EGR valve's vacuum hose back to the EGR modulator, remove it and test it for leaks, i.e. cracks or holes.
reinstall if it is good.
Remove the other vacuum hose from the EGR modulator, and follow it to the intake manifold, remove it and check for leaks and cracks.
reinstall if good.
EGR modulators rarely fail, not never it just isn't common, you can remove the connector and apply 12volt or even use a 9volt battery to test if it "clicks", also put that 3ft vacuum hose on it and suck on the end while activating the Modulator, it should release "your vacuum" when activated.

Now the DPFE sensor.
Where the two hoses go matters, so remove only 1 at a time, they are usually different sizes but not always, check each hose for leaks, they are on the hot exhaust pipes so can get brittle and crack on that end.
If both hoses are OK then time to test DPFE with Voltage meter.

DPFE will have 3 wires
Ground
5volts from PCM
Voltage out to PCM(varies from 0-5volts)

You will need a Volt meter and a sewing pin or safety pin to pierce the wire to test voltage.

Google: test Ford DPFE sensor
 

mjonesjr

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P0401 is almost always the DPFE starting to fail, looks can be deceiving.

Here is how the EGR system works so you can eliminate other possibilities before replacing the DPFE.
There are 3 parts for the EGR system, not counting the computer(PCM)
1. EGR valve and tube, this valve is opened by applying vacuum to its port
2. EGR modulator(solenoid or activator), it is a 12volt vacuum valve, it passes vacuum to the EGR valve, PCM controls this by sending it 12volts, it is often a pulsed 12volts, not simply an on/off, this allows PCM to open the EGR valve a little or alot.
3. DPFE sensor measures the pressure difference in the exhaust manifold, it has 2 hoses, one is near or on the EGR tube, the other is on the exhaust manifold.
When PCM opens the EGR valve the pressure in the hose on/near the EGR valve/tube will drop, how much it drops tells PCM now far open the valve is, so how much exhaust gas is being added to intake.

P0401: Insufficient EGR Flow Detected
This code comes from the DPFE sensor telling the PCM that there is no or little pressure change after PCM has started to open EGR valve.

It could be the EGR valve is not opening, so leaky vacuum hose back to EGR modulator or valve is broken.
Get a 3ft piece of vacuum hose that will fit EGR Valve port, install it on the EGR valve, start engine, suck on the end of the hose, create a vacuum, EGR valve should start to open and engine should start to run rough and even die, EGR valve is working.
Follow the EGR valve's vacuum hose back to the EGR modulator, remove it and test it for leaks, i.e. cracks or holes.
reinstall if it is good.
Remove the other vacuum hose from the EGR modulator, and follow it to the intake manifold, remove it and check for leaks and cracks.
reinstall if good.
EGR modulators rarely fail, not never it just isn't common, you can remove the connector and apply 12volt or even use a 9volt battery to test if it "clicks", also put that 3ft vacuum hose on it and suck on the end while activating the Modulator, it should release "your vacuum" when activated.

Now the DPFE sensor.
Where the two hoses go matters, so remove only 1 at a time, they are usually different sizes but not always, check each hose for leaks, they are on the hot exhaust pipes so can get brittle and crack on that end.
If both hoses are OK then time to test DPFE with Voltage meter.

DPFE will have 3 wires
Ground
5volts from PCM
Voltage out to PCM(varies from 0-5volts)

You will need a Volt meter and a sewing pin or safety pin to pierce the wire to test voltage.

Google: test Ford DPFE sensor
Thanks.

I know the elbow going into the front of the intake on the passenger side is good. I followed its hard plastic tube around the back of the motor to the driver side valve cover and it was loose there. I pushed it back in, but it was still a little lose in the valve cover. Is that connector that goes into the valve cover something that I can get to replace it?

I will do the other test tomorrow when I get home. I appreciate the help in advance.
 

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You are talking about the PCV(positive crankcase ventilation) system hose in the above description, it isn't related to EGR system or code 0401
 

mjonesjr

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You are talking about the PCV(positive crankcase ventilation) system hose in the above description, it isn't related to EGR system or code 0401
Thanks for the info. I read somewhere online that it could cause the P0401. Thought it was worth a shot to check.

I will report back when I go through all the test above.
 

RonD

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Always good to check for vacuum leak, and that's a common leak point on Ranger 4.0l SOHC.

Leaking PCV elbow caused P0171 & P0174, lean on bank 1 and 2, sometimes just one or the other
 
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mjonesjr

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Always good to check for vacuum leak.

Leaking PCV elbow caused P0171 & P0174, lean on bank 1 and 2
I haven't had those codes, yet. When I removed the brake booster vacuum line to work on the wiper motor, it had good vacuum in it.
 

enjr44

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Always good to check for vacuum leak, and that's a common leak point on Ranger 4.0l SOHC.

Leaking PCV elbow caused P0171 & P0174, lean on bank 1 and 2, sometimes just one or the other
As I once found out on my 02!!!:beer: The code for just the left bank really got me!!!
 

mjonesjr

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I "think" I found the problem. The EGR Vacuum Solenoid had the lower vacuum stud broke off and someone had stuck a screw in the hose to fill it up.

I'm going to replace the Vacuum Solenoid (Modulator) and see if that fixes the problem. The DPFE looks brand new.
 

mjonesjr

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I replaced the EGR Vacuum Solenoid and now I'm getting a P0403. Everything is plugged in as it should be without any vacuum leaks.

The EGR functions as it should with applying vacuum at idle and the truck shudders and almost dies.
 

RonD

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Could be a fuse blew or just a loose wire inside the connector.

P0403 is EGR Solenoid Circuit Malfunction

Nothing to do with EGR valve, DPFE, vacuum or hoses, just a straight electrical issue
 

mjonesjr

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Could be a fuse blew or just a loose wire inside the connector.

P0403 is EGR Solenoid Circuit Malfunction

Nothing to do with EGR valve, DPFE, vacuum or hoses, just a straight electrical issue
It didn't start giving the P0403 until I replaced the broke vacuum solenoid. I'm going to get a replacement one and see if that fixes the issue.
 

RonD

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You got the P0403 after you replaced the EGR solenoid, and P0403 means solenoid wires are not connected, so..............................check the wires on the solenoid.

P0403 would have come up before if there was a problem before, so only logical reason it came up after you replaced the solenoid is that either the new solenoid is bad, it happens, or the connector is not "connecting"
 

mjonesjr

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I've got a new one that should be in tomorrow morning. This morning when I started the truck, the CEL came on instantly for the P0403. I unplugged the EGR VS, plugged it back in, and reset the CEL. I drove to work and checked the CEL and only had a "pending" CEL for the P0403, but no light.

I'm going to replace the EGR VS tomorrow and check the wiring to make sure it is good. I'll report back.
 

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