And Odd DCS Signal issue...

Removing the B unit won't do anything since the B is a dummy. Based on the symptoms you describe, it sounds as if you have a DCS signal strength issue on one corner of the layout.

This can be caused by, among other things, dirty wheels, track or pickup rollers; a wiring issue; or loss of the signal while traversing a switch that operates using track power (this is dependent upon the nature of the switch motor).

Also, if using MTH RealTrax or Atlas O track, you need to remove the blackening on top of the center rail. If using Ross or Gargraves track, you don't need to remove the blackening, however, you do need to clean off the center rail's oily protective coating.

As for why it only occurs with one engine and not with the other, different engines have different spacing on pickup rollers, and traction tires (electrical insulation) on different wheels.

This and a whole lot more is all in "The DCS O Gauge Companion 2nd Edition", now available for purchase as an eBook or a printed book from MTH's web store site! Click on the link below to go to MTH's web page for the book!

Thanks Barry!

I think it's down to the engine itself.  Everything seems tight on other engines (ie: no issues I can measure).  My next step was to clean wheels and pickup rollers.  If that doesn't work then I'm not sure what my next move is.  The only difference with the F3 is that it is the only multi-coupled engine with multiple tethers.  That's kind of why I wanted to remove the 'B'; I know it's a dummy but it does have tether connections and does pass signals.  

I was originally worried about the switch, but I have 2 switches on the other loop and have never had signal issues there on any other engine.   I could swap the switch with an plain O-60 curve and see if that has an impact.  

It is Lionel Fastrack, BTW.

Thanks again and I'll try to report back!!!

New engine...Run the hech out of it, probably needs a little break in time to clean the rollers and  wipers for outside rail???? I'm really not sure if PS-3 has wipers for the outside rail pick up. hope not, ....

 Not sure how odd this is, but I am experiencing the almost exact same problem in one corner of my layout.
 Normally I run lash-ups and I'm finding that when I check signal strength it varies depending on what engines I'm running. Usually the 5v PS2 engines seem to have consistent 9-10 in signal strength while the 3v PS2 combinations normally will get a 1-3 at best. If I check signal strength with any of the engines (5v or 3v) by themselves it remains around the 9-10 range, but as soon as I lash up it falls apart. I have always been checking strength while the engines are running at about 15mph.
 My loop is 30'x44' and about 150' total length of Gargraves track with two Ross #175 double crossover switches. The loop is broke into four even blocks. I am powering the loop with one TIU fed by a Z4000. The TIU is located in the center of the loop with a no.12 wire going out to each block.
 I have tried a light bulb and/or a capcitor-resistor filter in many different combinations and nothing seems to work.
 I have also tried tying all the blocks together as one continuous loop, an saw no improvement.

 I have other loops of equal length that are a continuous loop(no blocks) but have the same wiring configuration ie: TIU in the center and four no.12 drops feeding each loop, and at least one Ross double crossover switch. I have one light bulb at the TIU on those loops. I can get consistent 9-10's with almost all PS2 engines in a lash-up or alone.
 Any suggestions?

 Thanks, Scott