Hey everyone, thanks for looking. I used to hang around in the forumns for older trucks a lot as I had a 93 f150 but I just recentley purchased a 97. Moving up in the world!!!! Nice to meet everyone. Now down to buisness.

I have a 97 f150 lariat 4x4 with the 4.6.

First I am wondering how many drive cycles or miles until the check engine light eliminates a code that is no longer being detected.

Second, I am having trouble diagnosing an p0401, go figure. I have been using a voltmeter, vacuum gauge, and propane to find vacuum leaks and nothing. When I apply vacuum the the egr valve it moves as it should but should it hold vacuum without me applying more?

Thanks again guys.

 

Yup. See this video showing the action of the EGR off the vehicle with the vacuum being applied.

 

When you moved up to 97 you moved into a different world.
First is to look up the 401 code.
What does it say?
Low flow on a test by the PCM.
That means the exhaust flow from the exhaust manifold to the EGR is stopped or can't be detected. Nothing to do with an intake leak.
The DPFE measures that flow. When detected out of expected limits it sets the code.
It could be the ports behind the EGR are plugged with carbon, or the DPFE is faulty.
A way to prove the port condition is apply vacuum to the EGR while the motor is running. If the motor gets rough or stalls the ports are still open.
That leaves the DPFE.
The DPFE measures pressure difference across a calibrated orfice within the tube. That's the two small hoses from it to the tube.
Once cleared it take two drive cycles to test the operation again.
If you clear the code, the PCM does all the diagnostics from scratch.
Good luck.

 

Here you go a picture. This is on the bottom side of the throttle body elbow that bolts down to the intake. You can see the 2 holes those may need to be cleaned out. Bluegrass. When you say 2 drive cycles what does that mean start/stop start/stop. The only reason I'm asking because I just finished changing spark plugs and wires to clear a P0303 code on a 97 4.6L and I went ahead and left the CEL on to see if clears on its own. Or will require the 100 or so miles to clear. The truck is no longer missing or stumbling. We drove it today about 10 miles. Started it and Stopped it 3 or 4 times

 

A whole new world within Ford at least!! I have found some distinct similarities between the two but I have lots to learn.

I have done tons of diagnosis but im still at a loss. If you wouldn't mind reading through what I have done so far to tell me what I am missing.

First I took off the throttle body spacer and cleaned it, it wasn't that dirty. Then after putting it back together I tested the egr valve by applying vacuum and the engine stumbled like it should. I did end up replacing the valve though just because it didn't hold vacuum very well. Then I tested evp (i think that's what it is called, the vacuum solenoid) and it tested good for voltage and resistance. Then I tested the dpfe for voltage and got 5.06 for reference and 1.02 for signal hot and cold. I replaced it and tested again but the numbers are the same. Then while monitoring the new dpfe signal voltage I manually opened the new egr valve with vacuum and the number stayed around the 1.02 mark.

What now?!

The reason I checked for vacuum leaks with the propane is to see if the line that is supposed the open the egr valve is cracked. Idk what else to do.

Thanks again guys

 

Did you replace the DPFE with a Ford OEM part?
Are the hoses on in the correct order. One is a bit larger than the other for reference.
The EVR solenoid, did you check for operation?
It is a 3 port device. In, out and bleed-down actions.
It has a filter under the round cap that filters air let back into the EGR once the vacuum is removed.
Make sure the EVR is not frozen with dirt. Electrical and resistance test won't detect this. The 'electrical operation' of the EVR is monitored by the PCM but your not getting a code for that.
.
401 test:
The PCM request the EVR to open the EGR under 'pulsing' conditions to control the amount of flow expected to be measured.
The DPFE measures the pressure drop across the orface and reports the value back to the PCM to compare to a fixed table.
The accuracy must be within 2% or better so everything has to be right on.
.
After you clear the code you can see if vacuum is reaching the EGR by putting a TEE in that line connecting to a vac gage.
Go for run to attain OD above 45 mph with very light amount of throttle. You should read about 2 to 4" of vacuum depending on the amount of throttle you have applied. This would prove that the EVR is commanded to open but the DPFE is not reading the correct amount of flow or the DPFE is faulty.
Remember that the PCM test is separate from the dynamic operation as you drive.
The test is when the fault is detected and the reason it's done.
The 'test' is done two times to be sure the lines are open in winter and not frozen with moisture until the engine bay warms up. Exhaust has high moisture content along with contaminants.
Two failures in succession is a logic failure and sets the 401 code.
This tight requirement is by EPA mandate to pass that engine family for sale to the public because it deals with Nox emissions the cats don't fully clean up.
There is more to this whole operation but you don't need to know it for now to solve the issue as it would only add confusion.
As mentioned before your into a new world of computer control.
Your 95 ECM ability running the old motors is way below this level.
Good luck.