The car has been running fine until now. Regular fluid checks and changes. Drove home the other night, ran smootly and everything seemed fine. Next morning, cranks but no attempt to start. Chekced: spark (ggod to plugs); fuel: (good to fuel rail); timing belt: (tight and in good shape); injectors: (electronicallydiagnosed as good last week); checked fuses: (all OK). The PGM-FI light comes on sometimes, but the previous owner says it has done so for over a year, and since I've owned the car I have had the same experience. However, there has been completely smooth operation whether on or off. (no stumbling or surging). Passed smog a month ago and up until now has started immeiately. Now it cranks, but no start. Because of the sudden nature of the proglem
I am suspecting a sensor or relay problem, but I am at the limits of my experience. Any ideas?

If the Check Engine Light comes on and goes off after 2 seconds, when the ignition switch is turned to ON (Position II), I would replace the Ignition Control Module. The plugs may be firing but not when the ECM wants them to. If, after replacing the ICM, the problem persists, I would replace the distributor housing (genuine Honda only)--internal sensors (CKP, TDC, and CYL) may be failing.

TXGreaseMonkey, thanks for the response.

Theis is a 1987 Honda Prelude SI. It is OBD I, so it has no check engine light. Is there something else I can check?

It's hard to believe that you don't have a CEL. My 1993 Civic is OBD I and it has a CEL. My neighbor has an OBD I 1988 CRX and it also has a CEL. Regardless, I would still go with the suggestions.

I had the same problem with my 87 Prelude SI. I replaced many things like the main relay assembly, but it ended up being the O2 sensor. An easy $50 fix.