Po401,po304

PO401 - EGR flow insufficient and PO304 - Cylinder 4 misfire.
Is this a sure sign of clogged EGR ports or what ? The vehicle seems to be running fine but When I whent to get it smoged I was informed of these two codes along with a burned out check engine light. I replaced the light, and sure enough, it is staying brightly lit. What to do next ? Any suggestions?

- Mark-

Model year?

Model year?
It is a 96

Thanks, Mark

I am not too familiar with the 96s but your problems definately COULD be caused by clogged EGR ports. (assuming your year has individual ports internal to the intake system)

Agreed, I know the '97 3.8L has them. If you do, it will not hurt to do the lower intake cleaning and a IAC cleaning if you haven't done them yet. You can search on these topics and get a step-by step procedure on them.

Thanks for the info. This 96 3.8L has high miles ( 162,000). It is a clean vehicle that I picked up cheap for driving around town. I was told that the oil had been changed often . By the physical condition of the vehicle, it appears to have been well maintained. At this point I just want it to pass the E - Check.

From what I have been reading it seems most likely that the EGR ports are the problem. Should I proceed with the port cleaning process or check The EGR system first ? Is the misfire indication a sure sign that it is the ports and not just the Egr system ?

Is there a possability that if I reset the CEL, and take it in right away, that it will pass the E- check. It is currently running great, plenty of horse power, and does not seem to be missing. I could tackle the Egr problem later?

It may be the DPFE sensor. Which is right in front of the egr valve, its square with two hoses going into it along with an electrical connection.

If you are having EGR troubles it is doubtful that you will pass emissions.

The DPFE is also a common problem and can give the insufficient flow code but it does not address the misfire.

You can test the dpfe with a voltmeter and a vacuum pump and a Haynes.

I still think you may end up cleaning your EGR ports. On my 99 it is not a huge job. About 6 hours but relativly straightforward.

Md,
I have a '96 3.8L.
99.9% chance that the problem you have is clogged EGR ports.

P0304 is a missfire at cylinder #4. That is the front passenger side of your engine. The ports clog closest to the EGR valve first.....and Cylinders #1&4 are the last to become clogged. So now....pretty much all the EGR flow is through Cylinder #4....which causes the missfire.

I have been down this road...last year.
I posted some pictures at

http://community.webshots.com/album/201931518cScpNK

that show the EGR ports.

There are a lot of vaccum connections on the back of the upper intake manifold....I have a picture of the back of the upper intake manifold posted....and you can see the places that things connect.

I removed the throttle / cruise control cable bracket from the throttle body......then removed the throttle body....and set it aside....with the throttle / cruise control cables still attached.

The upper to lower intake manifold gaskets are reusable....and are most likely good....

If you are ambitious.....while you have it apart....you might want to physically remove and clean the spray ends of your fuel injectors....as they tend to get a buildup of crud inside the end cap. I have a couple of pictures showing this as well.

To clean the injectors....you want to release the fuel system pressure....which is done at the needle valve that is located at the center of the front fuel rail (the fuel rails are crome).
You do NOT need to disconnect the fuel line from the fuel rail.....
Next....clean the dirt from around each fuel injector....where it goes into the head. I know you have dirt there....because that is a major dirt trap. You want to prevent that dirt from falling into your engine as much as possible.
Then, releasing the clips on the fuel injectors....and pulling up on the fuel rail.....remove the fuel rail.....and set it aside....you have enough play in the flexible fuel line to do this.
You may have an injector or so come up out of the head in the process.
Remove each fuel injector....and spray carb. cleaner up inside the end cap....to flush the crud out.....it will come right out.
Then....reassemble....making sure that you get the fuel rail firmly clipped onto each injector.
What I did......once the fuel rail is fully in place...but BEFORE I installed the upper intake manifold.....turn the ignition key to ON....but not start. The fuel pump will pump the fuel system up to pressure......Check for leaks.....you will be easily able to inspect each fuel injector to fuel rail connection and see any leak(s) that may be present. I did not have any leaks....but was the best time to see and correct them...if they are present.

I mention the fuel injectors as you have done much of the work to get to them.....and I was back in to clean them for another misfire issue that came up not long after the EGR port cleaning. I use fuel system cleaner in the gasoline.....and still needed to do the physical cleaning.....


When you have the upper intake manifold off....is is NORMAL for there to be some oil present in there.

www.autozone.com has repair instructions and show the correct sequence to tighten the upper intake manifold bolts. They also give the correct torque.....take note that it is INCH/lbs......so you do not want to over do it. But have them tight enough to prevent vaccum leaks.

You might also want to check the condition of the spark plugs. My originals were still working great at 135K miles.....but I found that the rear 3 plugs had significantly increased in gap size.......which places additional stress on the ignition system. If you need to replace them.Use ONLY Motorcraft Double platinum plugs as specified. They will be good for another 100K miles.

Armed with my Haynes manual, and all the information from this site, I will soon begin the project of cleaning the ports and injectors. I will let you know how it goes. Thanks , again, for all the help!