Thanks for the suggestion, but it hasn't worked.  my locos are both back to address 03 (factory default) but they still don't work worth a darn. 

I used Page mode to program them on my programming track.  first I read the value of cv08 and it read back '101'.  I wrote '8' to cv08 and while it did change the loco address back to 03, no change in operation.  that is when I went to read back cv08 and it still reads '101'.  Is the decoder fried?

At this point I am with you thinking this is something in the decoder.  Is there a list of the cv's and the settings for it available?  Maybe I can poke around a bit and find something that isn't right.

Thanks for your help.  I would hate to relegate these engines to a display case.

Well, that was my thought too.  I used an ohm meter between sides of the wheels and found that the wipers are picking up power fine.  I then took the locomotive apart and found that there is perfect continuity between the wheels and the circuit board on the engine.  Still doesn't work without touching the locomotive.   

I then tried reprogramming the engine number....no improvement.

I am quitting for the night because right now throwing it against the wall is starting to look like a viable solution!

Oh, and by the way other engines running on the same track ran PERFECTLY.  just not either of my S4's.

I Purchased one of the n scale S4's and liked it so much I ordered another.  I was running it on my test layout and it ran perfectly for an entire 3 hour operating session.  The next time I ran them (in DCC mode and they have the same address as before, both engines are #15) and the more I ran it the more trouble I began having with 'dead spots'  I recleaned the tracks and other engines run with no problem, but not the S4's.  In fact they have become so spotty on the power pickup that I just can't use them at all.  I cleaned the wheels and even took the truck frames off and cleaned behind the wheels.  there wasn't much there to clean as very little came off on the alcohol soaked paper towel I was using a bit of to reach behind the wheels.  I think I need to take the driver axles out and directly clean the wipers, but really, after the extremely minor dark spots I got with much cleaning, I am not sure this is the problem.

If it is, how do I get the wheels out of the truck after the bottom is off?  I dont want parts flying all over.

thanks for your help in advance.