DPFE & EGR Function & DTC's

[Windywoes]

While trying to find the cause of a persistent miss I have been looking at my DPFE & EGR functions. My question is why should I diagnose (meter tests) these devices when the PCM supposedly continuously runs tests on them and has seven DTC's for just the DPFE alone? If either device were malfunctioning wouldn't I get a CEL?

Be patient with me; I've got a lot to learn.

[wiswind]

You are correct.
One test that you can do to see if the EGR system is causing the persistant miss.....roughness......
Remove and plug the vaccum line that goes to the top of the EGR valve.
Take the vehicle for a drive.
Does the problem still exist?.....
if yes....the problem is not the EGR system.
If no...then the EGR system is the problem.
Reconnect the vaccum line to the EGR valve.....

NOTE....this should cause the CEL to come on with a code for insufficient EGR flow.....this is because you have disabled the EGR system.

It is RARE for the EGR valve to stick open.

If the rough running went away with the EGR system disabled....then I would suspect the EGR ports in the lower intake manifold needing to be cleaned (I think I saw in your other thread that you have already checked this)......2nd would be the DPFE.

[danielsatur]

It's cheaper to learn from everyone else ,see
http://www.automotiveforums.com/vbul...d.php?t=971132

If you suspect a bad EGR system, you can put a turnicate on it for the short.
A bad EGR or DPFE can act like an open window to your intake.

[Windywoes]

As you can probably determine from my posts, I am not a very knowledgeable mechanic, but I am willing to try things and learn things along the way. My gut says the problem is related to the EGR system. It looks like I have ruled out a bad EGR valve by driving with the EGR plugged and it still coughed. So my immediate plans are to re-test the function of the rather new DPFE and then take out the injectors for inspection. I have grown weary of buying parts so these possible solutions will not cost anything.

Although I have cleaned the EGR ports, is it possible that there could be an obstruction between the ports and the port where the EGR valve mounts to the block? I did not see any obstruction on the EGR side where it mounts to the block.

I am grateful for everyone's help.

[wiswind]

The test that you did.....removing the Vaccum line to the EGR valve has eliminated the EGR system from causing the problem.
You will NOT get rough running from the EGR system not opening when it should.
I have found that the EGR system from the EGR valve up to the EGR ports does not seem to become clogged.

You can drive yourself crazy looking into the various systems on the vehicle.....so if you are feeling a bit overwhelmed.......do not feel bad.
This is why I suggested the test that I did....as it will confirm or eliminate the EGR system from your list.

Do not forget to look into possible vaccum leaks.
One place to look is the PCV hose.....that goes from the PCV valve to the intake manifold. Oil can soften the hose and cause it to crack, etc.
Look for any disconnected, cracked....or otherwise defective vaccum lines.
There are quite a number of them....any one of which can cause a vaccum leak.

Also, give the IMRC links another look to make sure that they are connected and working.

One other thing you might try.....as it costs no money and is easy.
When it is dark outside.....lift the hood while the motor is running at idle......look for any signs of sparks, etc.
You want to look particularly close around the spark plug wires, coil pack.......
I know that they are new.......but I had a friend that detected defective spark plug wires....(NEW premium ones) that were lighting up like a city when he did this check.
BE VERY CAREFUL under the hood as you don't want any part of you or your clothing to get caught in any moving parts while looking around in the dark.

[Windywoes]

Thanks for all the tips, Wiswind. I will look for arcing in the dark in just a little while.