Next time it refuses to start don't wait for it to make up its mind-do below immediately to determine if its fuel or spark problem

http://www.2carpros.com/articles/car-cranks-but-wont-start

Get a helper disconnect a sparkplug wire or 2 and ground it to the engine atleast 3/16 away from ground-have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel related problem, Do you hear the fuel pump come On when you turn key on? If not check fuel pump fuse and fuel pump relay if okay-check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs,coil's resistances,cap and rotor,distributor pick-up coil, ignition control module, cam and crank sensors and computer Note: If it doesn't apply disregard it and keep testing

Answered by rasmataz
68 questions asked

mine is a diesel so does not have spark plugs. ill give the fuel pressure a check and let you know how it goes. thanks for your help. much appreciated

Response from rascal_ash3
1 question asked

Hard start for a diesel can mean several things, poor fuel quality is one, lack of pressure is a possibility too. If there are no currently present faults, there may be an issue with a main or fuel pump relay becoming intermittant. BMW did'nt import the diesel cars to the States in 2005. Are you in Europe?

Answered by Dr. Hagerty (expert)
9,669 answers provided