got a problem with ignition

my friend got an 88 crx si.. it will start up and run for like 5 mins and then just shuts off like someone turned the key. we replaced the ignitor, we put my si ecu in, took the old alarm out cause it had ignition kill on it, put it in time, and it still shuts off after about 5 mins and then u have to wait like 30 mins till it gets spark again.... any ideas what this might be? n e help would be greatly appreciated by me and him cause it is driving us nuts... o and its not throwing any codes on the ecu

check the plugs, plug wires, the coil, and check for any loose wires going to the distritubutor or ECU.