Oil furnace repair turns on and off fast, like it is not igniting ?

Observe it closely, open the little inspection shutter. During the cycle does it actually ignite a flame for 2-5 seconds before it shuts down? If it does then the problem is either a dirty or failed flame sensor, clean the sensor eye ( 75% ) or replace it (20%) if it still will not maintain fire then the control module is bad.

If it will not fire at all, remove the burner assembly and inspect the ignitor tips, and combustion chamber. If the tips and chamber are dry you have a fuel delivery problem, clogged filter There are 2 by the way the big one by the tank and a little one right where the fuel enters the injection pump, empty tank, air leak in the suction line or injection pump failure.

If the tips and combustion chamber are wet with oil then dry the ignition tips off and buff the very ends with emery cloth and make sure they are not bent apart ( less than 1/2 inch gap for most models but basically look to see that the electrodes are parallel to the point that they are symmetrically angled towards each other. Make certain that there is not an excessive amount of fuel pooled in the combustion chamber ( wipe up excess with paper towels ) then re-install the burner assembly and try ONE more time while watching for a bright flash ( spark ) just after the motor starts, no flash and no fire will mean a bad HV transformer.

if an oil change hasn't been done recently, than have this done..fuel injector's could be dirty..or moisture in the gas line..try a higher octane..or a boost to the fuel you have at almost a full tank, at least 2/3's.