wrote:
> Greetings,
>
>
> I wanted to run my troubleshooting steps past some of the more
> experienced. I have a 97 F150 4.6L throwing a P0401 (EGR insufficient
> flow). I think I have a bad EGR Vacuum Regulator solenoid.
>
>
> I've disconnected the green vacuum line from the EGR Vacuum Regulator
> solenoid to the EGR valve and applied a slight vacuum to the EGR
valve.
> The engine RPMs down almost stalling. I'm guessing the EGR value is
> okay. Reconnected.
>
>
> Moving to the EGR Vacuum Regulator solenoid. After engine warmup, I
> checked the voltage on the EGR Vacuum Regulator solenoid connector.
It
> showed 12-13vdc. I assume that means the EGR Vacuum Regulator
solenoid
> should be open.
>
>
> Reconnected the plug to the EGR Vacuum Regulator solenoid and pulled
> the green vacuum line off the EGR valve, put my finger over the end
and
> could feel a very slight pulsation.. no vacuum however. I lightly
> tapped the EGR Vacuum regulator solenoid with no change. Reconnected.
>
>
> Disconnected the white / green vacuum line combo at the bottom of the
> EGR Vacuum Regulator solenoid. The white line had a solid vacuum on
it.
> Reconnected.
>
>
> If I understand the diagrams correctly, the EGR Vacuum Regulator
> solenoid should be open with 12vdc applied to the connector. This in
> turn should apply a vacuum to the green vacuum like going to the EGR
> valve.. resulting in the EGR valve opening.
>
>
> Do I have a bad EGR Vacuum Regulator solenoid or should I move on to
> the Differential Pressure Feedback EGR sensor?
>
>
> Thanks in advance.
>
>
> Jason

The regulator solenoid is the last item in line to control the EGR
valve, correct? It is ECM controlled. The ECM will ground one wire of
the solenoid in pulsewidth modulated fashion when it wants to operate
the EGR valve. You don't expect there to be power AND ground at that
solenoid at idle in park, do you? The resulting constant EGR operation
would make the engine stumble, which would be bad for everyday idle
quality and emissions.

Apply power and ground to the solenoid manually and see if it allows
vacuum through. If this is OK I would suspect the DPFE. You should
find testing procedures for it in a Ford manual and/or discussions
about it online. If it has stuck or failed internally, it will
register the wrong pressure (in the form of a 0-5 volt reading) to the
ECM, and can cause inadequate or excessive EGR flow codes depending on
how it fails.

The voltage of a DPFE is low when there is no EGR operation and
increases with EGR flow.

One more thing... normally 4.6s clog exaust and intake feed passages,
but I don't know how the intakes and crossover tubes are set up on the
F150 version of the 4.6. They may be different. At any rate, you said
the engine stumbles pretty hard with manual EGR activation. This is a
good sign, but doesn't eliminate the possibility that the passages are
partially restricted or that several individual cylinder runners aren't
totally blocked.

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