The EGR valve is clogged on the backpressure port, that is the small tube that you need to clean the EGR valve needs to be replaced unless you are sure that air can pass through with the egr valve opened.
The engine light needs to be reset it does not automatically turn off. In some cases if the egr valve is known to be good as well as the modulator there may be a problem with the vacuum switching valve(VSV) that controls the egr system and this vsv may need to be replaced.
P0401 = Exhaust Gas Recirculation, insufficient flow detected
Start by inspecting the EGR for obvious faults such as vacuum leak on the supply line. Also check to make sure the EGR is opening when vacuum is applied. A vacuum tester should work well for this test.
Check for
vacuum leaks on intake manifold,
the air tube between the air filter.
intake manifold vacuum hose.
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clean throttle plate with Berryman carburator cleaner
SEE sample picture HERE
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Also remove carbon built up behind the EGR valve and the EGR passage tube.
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Vacuum leak WILL offset the intended 14.7 to 1 air fuel ratio.
More un-metered air (leaks) will lean out the fuel mixture.
Use small amount of Berryman carb clearer at potential air leak area will help you identify trouble spot.
At idle,just spray and listen for the RPM surge.
The in-rush of carb clearer will increase the RPM on the motor.
Record the problem spot(s) and address it later.
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EGR carbon built up require 2+ hours to clean from start to finish.
You will need a new EGR base gasket before your start.
Locate and remove the EGR valve after the vehicle is cool down.
Carefully record the connector and vacuum line (for older vehicle) location by drawing an easily to follow diagram.
Remove the EGR valve.
Inspect the location of the carbon built-up inside the valve and the EGR passage tube.
SOAK these areas with WD-40 spary.
You will need a small screwdriver,cloth hanger and lot of newspaper and time to get this cleaning done right.
RE-SOAK the carbon and let it sit for over-night will also help.
One the last round,pass a shop vacuum of the EGR valve and the passage pipe.
Install the new EGR gasket and connectors.
Allow the vehicle to warm up outdoor to burn up any remaining WD-40.
Take it for a test drive.
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Cheers,
Mustgo
Where is the vacuum on a 2000 expedition 4.6?
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