My question what is the problem of bmw car 5 series engine wont start but has cranking?someone pls give some advice

Have you checked the spark and injector pulse

run the fault codes
check that the immobilizer is operational ( fob key battery)
check for broken timing belt/chain
check crank/cam position sensors
check the ignition control module

Your fuel injected could be blocked

If you've checked the fuel system, then check the "spark" end of things

Lets find out

1. pull spark plug any one hold about 1/4 inch from engine block(with insulated pliers) and have someone crank the car. You should see a spark jump across to the engine repeatedly . if so ing system is ok
2. You don't sat the year so pull the fuel line off where it enters the carb, throttle body or injectors whichever you have. put end in a jar crank eng just a little . if fuel squirts up into the jar pump is ok. should be a lot.
3. This will tell you which system is causing the problem

Hope this helps Mike

Assume you have gas. BMW does not like to start or run if the battery voltage gets too low (for example sitting in the driveway unused. It does not take long with all the electrical drain(computer, security, etc.). A peculiar item about M cars is if the oil gets 3 quarts low, the engine wont start to protect the engine. Other less common camshaft sensor, crankshaft sensor, ignition coil pack, fuel filter, fuel pump. If it does not crank but battery is fine, check the starter. Turn the ignition to ON but not START then if you cannot hear the fuel pump humming, the fuel pump itself or a relay to it is probably bad. Using a rubber mallet, give a couple of sharp blows to the underside of the fuel tank and then try to start. If it starts, fuel pump is bad. Fuel pump is located under the back seat on the passenger side-easy to get to.

wont crank?
or cranks robustly (the crankshaft spins fast) but wont start.
all cars that dont start one, all ran when new. etc.
what counts is the now. only.
you need to do the tests. all covered in the FSM or at alldata.com
i cant help you because you . cuz did not say crank or start? so......

1: test all fuses. (not just gandering, use a meter)
2: check battery voltage 12.6vdc rested.
3: if not cranking, wiggle the shilter (a/t) or clutch if m/T
if a/t? try cranking in Neutral. cranks now? bingo.
4: cranks ok, and fast so check spark/

ill end there, due to vast number of tests and no clear stated
symptoms.
ever give it a full tuneup (60,000 mile service schedule?) or this DECADE. if not why ask the spark plug question.

water in the fuel pump open the drain plug on the bottom of the pump.to drain it .then close it .now pump up the pump as hard as it will go .get someone to turn over the engine as you keep pumping .

If it fires only occasionally, my first suspect would be the crank position sensor (aka pulse generator). Should be on the front of the engine mounted very near the toothed wheel on the crankshaft,
You should check for fuel pressure at the fuel rail while you are cranking to see if it is a fuel delivery problem.

check for a spark if no spark and engine cranks ok then renew the ignition module