Dcs power fluctuations

Z4000 problem?   Tiu problem? layout problem?  where do  you start trouble shooting? I'd probably start with a replacement transformer.   Any old lionel transformer kicking around?

That was my next plan I've checked every thing else

I would start with an  AC voltmeter, at the transformer terminals, and work downstream from there.

Are you using both outputs or just one?  Do both outputs feed the layout in parallel (a no no)?  Do both voltages drop?  What is the amperage reading?

Could be that the operation is over 180Watts and your phasing both sides of transformer and it goes into protection mode. 

More likely you have loose internal connectors on TIU or to the track, or a periodic short.

I would remove TIU and operate conventionally and see what happens.  If still fluctuating either track or transformer.   G

What track are you using? What type of connections to it?

You may have been over drawing through it and it's finally failed somewhere. Do you have power going through your switches? Is it the whole layout or just a certain area?

I use only 1 input,gargrave track,Ross switches switches are powered by a zw.how can I determine wattage. The breakers on the Z4000 gave not tripped 

Where are you getting the voltage readings you state in original post?  when voltage drops, do amp readings on Z4000 change?  With those few engines, wattage not an issue.

You have to take voltage readings at various points, as I said above, to pinpoint cause.

Thanks for input from all rewired all connections,transformer,tiu,,terminal block. Problem seems to have corrected.Tom