2001 venture wont start sometimes one mechanic said crankshaft sensor but it is not throwing any codes.fuel pump is working.

Can be any thing -- next time happens need to figure out if problem is spark or fuel --- possibles that don't throw code fuel pump. Fuel filter air filter. Egr valve crankshaft positioning sensor Ignition switch Coil Etc these are just some of reasons have scanned for possible pending codes

Check the crankshaft sensor.

You don't say what size engine you have, but the two most likely candidates for imminent failure would be the crankshaft sensor or the fuel pump. If you have fuel pressure at the rail, then I'd replace the crank sensor fist, as they are common failure items.

Your best bet is to get a reading on the fault codes . Probably the crankshaft positioning sensor is faulty in which case sometimes it will start and sometimes it wont. Code reader should tell.

is there a check engine light, possible mass air flow sensor

Do the basic tests. If it cranks good but won't start, have a helper crank it while you check for spark at the plugs. If spark everywhere use a gage and check proper fuel pressure and fuel injector pulse.
Any applicable trouble codes?

ck fuel pressure ,map maf sensor.timing .

FIXYA ADMIN CHECK. Q APPROVED.

1) If you have any engine codes, these may be a clue. 2) Check air supply, clean filter, not blocked? 3) Check fuel pressure. 4) Crankshaft position sensor, but this will throw a code, so you should have seen this from step 1. 5) Spark plugs & ignition modules - should also throw codes. 6) Fuel injectors

it is possable/likely a bad ECTS (engine coolant tep. sensor), this can cause the injectors to allow to much fuel into cylinders and cause a low compression and or flooding situation, good luck, marty