My 89 civic hacback only starts when it won't.starts great in the morning or when it sits but if I stop to get gas or etc.it won't start up un less the chack eigin light goes out it a good strong motor so I don't no

Perform the K-Test on the ECM, which may be failing:

The K-Test: Remove the MAP Sensor connector and turn the ignition switch to ON (not start). Using a multimeter, check for 5 volts going between the MAP Sensor connector's reference wire (+) and ground. As you look at the connector, this is the socket on the right. Really press the black test lead into a cleaned main ECM ground on the thermostat housing. If the voltage is low, it's probably indicating ECM failure. Most failed ECMs will record a fraction of a volt. To me, the K-Test is simple, elegant, and accurate.