My 2000 528i will not crank intermittenly

Does the crank sensor check good now?
check fuel rail pressure especially the fuel rail regulator. They commonly go out.

Based on your testimonial comment. I know how intimidating the ECM's can be. Another tool everyone should have is a ODB diagnostic system. These are now easy. Get a Kiwi3 - this plugs into the ODB connector under the steering wheel and converts all the signals to bluetooth. The get a program for cell, laptop, tablet etc to read all the information in the computer. The software that I use is ODBTech - pro version. This might help you mechanic husband learn and understand more about what's happening in the virtual ream.

Could be bad sensor whether crank sensor, sam sensor, idle air control sensor, bad ignition module, bad coil or even timing belt. if you have a service engine soon light/creck engine light it's more than likely a sensor. If no light, probably timing belt/fuel filter plugged/ or weak fuel pump.

The engines run very lean for fuel efficiency. Although a "cold start sequence" gives the impression of freezing temperatures, the operating range is much higher. The water temperature sensor (some have 2) may be staying too warm for the reset. You may need to change the sensor. Then the fuel mix will be richer and the engine will start.

when you have your hood up in the air can you hear the starter trying to make a clicking sound or no sound at all with the starter ? Starters also go bad too and some times it is intermitten some times as well. You can use a multimeter if you know how to use one that you can use one to test the starter red hot plug from the battery to it.

Sounds like you tested the alternator, how did you test the battery, did you take it out and get it load tested? If not it can still be the be a weak battery.

A bad crank postion sensor can be intermitten till it just fails, causing syptoms that look like you ran outa gas. So its one of 2 things (maybe both in worse case scenario) CRANK POSTION SENSOR, Or a fuel pump. Honestly I suspect a crank sensor if its the 4 litre engine. But like the poster said check the valve and see if any fuel comes out. If so you got yourself a bad crank sensor.

Also heard of some really really wierd issue with the PCM bolts grounding out the ECU, might try backing those out and it just may be the cause.

I hope this helps (remember to rate this answer).

Put a monitor on the starter...
How many miles on the starter (original or replaced)?
Always advisible to change it if older than 6yrs old or it may fry your battery, solanoid/coil packs, and starter.

Have it double checked... it is tricky as it is fickle.

Cheers

check spark from coils, make sure it is getting fuel...

the most common cause of intermittent no start issues as the crankshaft position sensor on this car.
I need clarification on your heater issue.

it is a loose ground to the starter. look for a ground to the bell housing. chances are it's loose this is the ground for the solenoid on the starter. I had the same problem with my vehicle . please rate this thanks

I want to thank u for reporting ur problem. I recently had to change my fuel pump and it just happened to have happened on the same day u had to change urs. I really think that after having a car for less than 2 years this should not have happened but I am no mechanic just a driver. But just wanted u to know that u should also have them do a fuel cleaning and flush out the injectors and a throttle body service. Good luck hope I have helped u out.