How to debug random crash/reset ?

Hi all,
I started having this error lately on esp8266. It's not triggered by a particular line of code. My code is a bit large to be included here, it makes a data model and read from a sensor.
It looks like I am doing something that make the esp unstable, but the code continue running to some point where the esp is stressed then the crash happens. I tried another esp8266 board and with v1.94, no change. It's probably my code then. I would like to find the code part responsible for this instability. How to learn more about what happens ?

Any idea how to debug this problem ? is an abuse of callstack a possible cause ?

Polypod

 ets Jan  8 2013,rst cause:4, boot mode:(3,7)
wdt reset
load 0x40100000, len 2408, room 16
tail 8
chksum 0xe5
load 0x3ffe8000, len 776, room 0
tail 8
chksum 0x84
load 0x3ffe8310, len 632, room 0
tail 8
chksum 0xd8
csum 0xd8
2nd boot version : 1.6
  SPI Speed      : 80MHz
  SPI Mode       : QIO
  SPI Flash Size & Map: 32Mbit(512KB+512KB)
jump to run user1 @ 1000
rLoading 7436 bytes from flash...