Have a 98 civic LX. It started to die recently and is now not drive able. It cranks up, runs 10-12 minutes then starts to sputter and dies. If I unhook battery and let the codes clear it'll do the same thing. Crank up, run for 12 minutes, then die. But it's not a temp thing. If I let it cool but don't clear the codes it won't start. Not timing. New timing belt, CPS, plugs, dist cap is only a year old, new Catalytic converter and O2 sensors, tried 2 different ecu's. All doing the exact same thing. Only engine codes coming up are for O2 sensors. Battery and alternator seem ok as it isn't dead when the car knocks off. I can sit an turn it over but it'll never start again until I unhook the batt for a while

 

Could be the distributor? Fuel pump relay? Although that doesn't exactly match to your symptoms, if resetting the battery, does sound like ECU is getting weird info back from computer. Have you run a diag to watch what's happening before it dies? For example, even though you replaced items, the ECU might not be reading them correctly (meaning perhaps a wiring short somewhere, as you said you replaced the ECU). I'd look to see what various sensors are spitting out. And what does the timing say while running?

 

The timing is set I think to 12* btdc. But I haven't checked it when it starts to sputter. I didn't assume the timing would change at all I didn't think the ecu would be able to do that unless it was a vtec or w.e. I'm not the best with hondas and mostly mess with older american cars but I'm missing the gas mileage lol
I think *12 but I could be wrong. I'll have to double check. It may be +/- 2*

 

Do you have a scan tool that can see engine sensor data in real time ? It sounds like you may have adaptation issues. You need to monitor the Primary O2 sensor "Short Term Fuel Trim" and "Long Term Fuel Trim" values... if these max out positively over the course of the ten to fifteen minute period in which the car runs and then slowly chokes out and dies... this would be an indicator of either a damaged/psycho Primary O2 sensor or a large exhaust leak in front of the sensor itself causing irregular/false readings. Also, check to see what the "IAT" (Intake Air Temperature) and "ECT" (Engine Coolant Temperature) sensors read. Upon cold start up, they should both read very close to ambient temperature. As the engine runs, it will slowly warm up and the ECT values will increase to operating temperature (typically between 178 and 200 degrees F). Whereas the IAT values should stay somewhere between the "outside temperature" and the "outside temperature plus 40 degrees" F. Once you begin driving, the ECT values should stay at operating temperature... if they begin to drop below 177 degrees F, you likely have a thermostat that is stuck open or partially open and this will also richen up the fuel delivery... affecting both fuel economy and potentially choking out the engine itself.