What is the value of the node voltage, V1?
It's been a while and no one has decided to close your question, so I'l write something short.

I think you are talking about this schematic:







simulate this circuit &ndash; Schematic created using CircuitLab

With KVL, starting at the lower left corner (at the ground symbol) and working clockwise, I get:

$$0\:\text{V} + 5\:\text{V}-I\cdot R_1-V_{Z_1}=0\:\text{V}$$

The top node of the zener diode, the node at \$V_1\$, will be more positive than the opposite zener node (bottom, at ground) and so you substract \$V_{Z_1}=4\:\text{V}\$ (or else add the negative voltage you worked out.)

You could merely observe that \$V_1=4\:\text{V}\$ and easily work out the current in \$R_1\$ as well as its voltage drop. Either way works okay.