1999 honda civic keeps shutting off while driving

Things need to be tested ie. proper spark , fuel pressure , injector pulse . Unfortunately in your case you have to do the testing when the problem occurs .

Wont start at all? Perhaps after it heats up to operating temperature the engine stalls? How far into run time does the issue begin? Is it intermittent or everytime the vehicle is operated? Typically a good baseline is ideal in a case like this. You have replaced vital components to the ignition. Other things to check to have a baseline, is fuel pressure and delivery at rail, also check pressure bleed off time and ensure they are within spec to manufacture, unless modified. Compression, ignition spark, timing, ensure all harness connectors are clean and well seated. Next steps, check ignition key cylinder function, wiggle while running and see if engine falters or stops running while whiggling key (watch RPM and listen to engine), check all fuses to ensure they are seated. Battery post connections (properly tightened) and alternator function (charging). This is a side note: torque spark plugs to proper torque specs, ive done head repairs that could have been avoided by properly torquing spark plugs. Once an aluminum head has stripped threads, its a nightmare and costly for something simple. Fill me in on your findings and we will go from there. Be as descriptive/detailed as possible with your responses. Thanks, good luck in your findings

Do us the favor and let us know when you find the problem , thanks