Hi all,

After cleaning the TB, carbon deposits, checking the DP Senor and growing tired of the P0401 poping up every couple thousand miles, I finally changed the EGR. I found out it was a aftermarket part and replaced it with a Motorcraft part. I also changed the oil and air filter will all motorcraft parts.

Well, now it is in for inspection. The inspection garage can't get it a emission reading (WTF). Did I do something wrong, or is it possible that the "system" hasn't cycled through? (1998 4.6L V8. FX4 Off-Road)

 

How long has it been since you cleared codes, disconnected the battery, or replaced the parts?

 

I did the cleaning and air filter replace this past Sunday and replaced the EGR a day ago.

 

Just go get a "U.S. Grant" inspection, they always seem to work good for me!

Good Luck!

 

Well, first the garage doesn't do emmissions testing.
They only look at the codes from the ECM and send that data to Harrisburg via telephone modem and repair what is a problem before final testing.
Next,what do they mean? Can't read anything?
If yes, the fuse for the test port is blown, pin bent or pushed back at the test port.
Find out what is the 'real' issue.
If codes were cleared then some monitors may not be reset.
Depending on what pid monitor is not reset, you are still allowed to pass as long as it's not emissions affecting. Example: a fuel monitor not reset is a 'passable' item in Pa. because it can take so long to auto reset (many hundreds of miles). A P4xx code is not passable.
Un set pids cause a code P1000 and don't turn on the CEL lamp.
Your garage has to look at the pids with a good scanner to tell if any are not reset and which ones.
Sounds like you need to go to a garage that knows what they are doing.
Good luck.

 

Thanks Bluegrass. There was problem with the test port. Everthing checked out fine and my truck passed emissions and inspection. 100 miles later, check engine light and a P0401 code. I have a new motorcraft EGR & O2 senors, the DPFE is good, and the vacuum pressure is fine. Only thing I can think of is that the Air In-Take value needs to be cleaned.

 

The p4XX codes are very tight in tolerence per the EPA.
All the possible faults are the sensor, the cabling to it, the EGR, the vacuum gateing device, it's cable/vac hose, the metal tube from the exhaust, the small hoses that attach the DPFE.
401 is insufficent flow.
Look for the following.
1. cracked metal pipe at the exhaust manifold or along it's length.
2. the small hoses split and not sealing the the DPFE.
3. The EGR not resonding to the gated vacuum signal.
4. the vacuum gate has an issue such as not allowing the EGR to close once opened etc.
5. plug-up not good or corroded.
6. restricted porting in the intake manifold after the EGR.
At the stand pipes, check that you can feel exhaust pulsing out of them with the motor running. Inside the bigger part of the pipe is a calbrated restriction that is used as part of the measuring standard the software uses for the test results. That must not be blocked.
Be sure to use only a Motorcraft replacement DPFE.
A tech with a scanner can access all these functions and make them operate so there really is no misterey about servicing the system.
The normal functions for these test are done at various times in the drive cycle. It take 2 test failures in a row to set a code.
The 401 test is done by pulseing the gate valve that opens the EGR a set % amount, then the DPFE measures the differencial pressure drop accross the calabrated orfice in the pipe. The DPFE pressure sensed value either is inside or outside the 'expected' value as a pass or fail.
Since this value is so tight for tolerence in the order of about 2%, any issue that affects the flow rate will be seen by the DPFE as a failure and is why this is such a high profile troube code with these motors.
Good luck. There's no more I can offer about the problem. It just has to be understood and run down.