crank but no start but it trys

[tck4321]

when it cranks, sometimes it will not fire. sometimes it fires and the engine shakes violently. other times it seems like it will start but it doesn't. i thought it maybe fuel related. form may understanding, the way to check fuel pressure is to tee into the line at the fuel filter. i don't have a way to do that. i can hear the fuel pump running with the key turned to start and the clutch out. then i wondered if there is water in the fuel and it froze. its pretty cold outside. i poured some fuel dryer in but it didn't help. still if there is frozen water in the fuel line rather in the tank then i don't see how the fuel dryer can get to it.

also, i removed the oil cap and i can see a cam moving during cranking. i'm not sure if these cars have timing belts or chains.

i'm not a stranger to cars. i just don't know anything about these. plus its really cold outside and i'd rather not spend a lot of time doing diag.

thank you for any help and ideas

[boyrs]

Index of /FSM/Sentra

2.5L or 1.8L? what kind of gas you using? what do the spark plugs look like? any oil on them?

[tck4321]

i kept cranking it and it finally started. runs fine now.