92 integra - S4 light flashing and does not start

Hi,
I have a 92 Integra, and when i try to start it, the S4 light in the indicator panel flashes, and it does not start. The starter does work, but engine does not start.
occasionally, it does start, but now it does not.
One mechanic mentioned it could be the transmission, another said it could be the speedo, found this in some other forums as well, others say they have connect to the diagnostics port.
is there any way of us connecting to the diagnostics port?
any help appreciated.
thanks