Fuel is a good guess; Is there a service indicator showing for information ? If not it's back to the basics. What is not working at the time of the failure, no spark, injection pulse, fuel pressure? The fault has to be found, then trace the error back to what controls that function. You've already spent money to address to problem, seek a person that can help you trace the malfunction, with the right tools/equip, back to the root of the problem.
Possible ; crankshaft angle sensor on the rear of the cyl. head, looks simular to a distributor without a cap. How about the "indicator" already ask about in #1 answer? Light on in dash while it's running? Good scanner is a must! Even IF no light is on.