I have been seeing my mileage drop in the last month or two, slowly enough that the change is only noticable as it accumulates. At first, I attributed it to winter diesel, or to the biodiesel feed stock changes. But I decided to try an experiment anyway:

I blocked off my EGR pipe, figuring that if a faulty EGR valve was the issue, the mileage would bounce back. Sure enough, it did. Yes, it threw at least one code (P0401), but only after I had blocked off the pipe. No CEL before, and no other salient indicator that anything was amiss. It takes at least one cycle of off-on driving for that code to trip the CEL, even with that completely blocked off.

So I would venture to guess that the EGR valve issue is more prevalent than we may realize. If you have a good way to get your codes read, and you've seen your mileage drop, you might want to check the codes. It would also be nice to hear that people who'd already had their EGR replaced are doing this, and that the replacement has indeed fixed the problem for more than a few thousand miles.

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George Reiswig
2005 Jeep Liberty CRD
Suncoast, SEGR, lift, InMotion tune, homebrew B100
At 138k, new head & gasket, timing belt, rockers and swearing vocabulary

I thought my CRD was running fine and getting good mileage till I threw the EGR code. Since it's been repaired it runs better is all ways than it ever did before.

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No one knows as much as all of us.

greiswig, How much of a mileage drop did you see? I've noticed a real drop of a hundred miles lost off of my range. This is still being run the same way and on the same fuel!

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Jason
'95 Dodge Cummins 550+HP #2 Diesel only, NO DRUGS!
'05 Jeep Liberty CRD, soon to have more ponies