Sometimes php5 process stress cpu

[bulforce]

i host around 15 blog sites... all using wordpress

What i notice is that every once in a while (lets say couple of days) the server get under very high cpu load... average CPU 70~80%

with "top" i can see a lot of php5-cgi processes and some of them shows [defunct]. I am kind of new to linux and so far the only way to fix this is to write killall php5-cgi which is helping for a while but then its happening again.

Can somebody tell me how can see which php file exactly is causing this high load, so i can dig into that issue... i mean some freak "ps dsuaby | grep -dkjsahu" command maybe.

System infomation
Pentium 4 3GHz
1GB ram
100 MBps uplink

Debian 4.0
ispCP 1.0.0 RC4 OMEGA
build: 20080308
Priamos

Thank you