To crank or not to crank.............

I bought a 97 Explorer XLT 4.0 SOHC with 110,000 miles for 750 bucks. Of course I had to rebuild the engine. What a job. Anyway the engine now has 1500 miles. The check engine light came last Mon., Sat.the wife drove the suv all day and parked it that evening. Ball pract. Sun. ,It doesn't start. Monday after work I was going to start trouble shooting. Tried key first, it started , drove around block,Tuesday at noon, it would not start. I replaced the crankshaft sensor. It started, but will it tomorrow? The trouble code is PO455. Any suggestions?

Your trouble code is for gross evaporative emissions leak. Either a line is off, broken or the gas cap was loose after fill up. When it will not start, does the starter engage the engine? Does it spin over normally, or kinda sluggish?

I replaced the crank sensor(a mechanic overheard me at the parts store and said to replace it). It starts everytime now. I'm trying to work out the trouble code PO455 (EVAP leak).What I,m noticing is that when you rev the motor the rpm goes down to 1000 then after a couple seconds drops to around 600. It seems the motor tries to pick back up, but it doesn't. Just stays around 600. All the research I have found so far on the EVAP system is to check charcoal canister, hoses , ends and the VMP. couln not find any leaks. About the only thing I couldn't check is the crankcase baffle. Its located under the lower intake. This being part of the vacuum system, would this cause the EVAP to display a leak? ie...vacuum leak ; I did replace the gas cap. Don't know if it helped.