I have an 06 BMW 325i, I’ve had it since December of 2013 and I haven’t had any issues until recently. In early June I went into the store and when I came out the car would not start, I kept trying to start it but I didn’t want to flood it so I waited about 30 minutes before trying again and it started right up. Fast forward to early July, I go into a store come out and the car won’t start, I tried giving it some time and nothing. I called a friend who is a mechanic and he asked me if I had gas in the car, I did, but it was very low. So, I got my gas can and walked to the closest station. The car started right up. So later that evening I went into yet another store and when I come out the car will not start. This time there was plenty of gas in the tank. I gave it time but it would not start. I ended up draining the battery and getting stranded overnight. In the morning, I called AAA to give me a jump but the car still would not start. After that I called a mobile mechanic to come out and diagnose the problem but as soon as he jumped the car it started right up. I was too afraid to turn the car off but he said that it was the fuel pump. I got home, turned the car off, I tried to turn it back on and it started right away but I let it sit for 10 minutes and it would not start and didn’t start again until the next day. I had someone else come out to diagnose it and they said that it was the fuel pump, so I had the fuel pump replaced but the car still would not start. It started several hours later but it was running very rough, the check engine light was on and the car smelled very strongly of sulfur. I had the engine code read and it said that cylinder 4 was misfiring so I purchased an engine coil pack and had it installed but that still wasn’t the issue keeping the car from starting. (I know that BMW’s can be tricky some times but I am recovering from a life changing tragedy and I couldn’t afford to take the car to a dealership or specialist.) I had someone else come out who said that it had to be the crank shaft position sensor, I had it replaced and the car still would not start. I finally had the car towed to specialist who only works on BMW’s. Initially, he said that the fuel pump was improperly installed, he re-installed it but the car still would not start, then he said that in the midst of all of this my starter went out, he replaced it and the car still would not start. Then he said that the fuel pump wasn’t providing enough pressure, installed a new fuel pump, car still would not start. After that, he said that it had to be the sending unit, replaced that, car still would not start. Now he is not answering or returning my calls. I use my car to make a living so I haven’t been able to work these past few weeks and I am desperate to get my car running again.
Thought number one have a check of the battery done, has it ever been replaced? if not do it now using a memory saver of course. It is surprising the number of maladies that can occur from such a simple maintenance item.
What needs to be determined first (assuming no diagnostic codes are set) is what’s missing; spark or fuel. A miss on one cylinder should not cause a no-start condition.
You might get a can of aerosol carb cleaner, spray a healthy shot into the intake tract, and see what happens. If it starts and runs for a second or two you can at least weed out a lack of spark issue and focus on the fuel system pump controls. If it doesn’t run or cough then it’s back to figuring out why there is no spark.
There seems to have been some guessing going on without thinking the problem through.
I’ve seen fuel pump relays act that way intermittently on BMWs. Is that one of the many things your “mechanics” guessed? It’s easy to switch another relay with the fuel pump relay next time it doesn’t start. The relays and fuses should be identified on the fuse/relay box cover. MANY relays are identical. If you switch a couple, use one that is not absolutely necessary to the running of the car, like the A/C relay if it is the same as the fuel pump’s.
I was initially thinking it was the fuel pump or fuel pump relay too. The reason is b/c you say you sometimes run the gas tank to nearly empty, and doing that can shorten the lifespan of electric fuel pumps. But later in the post you say it’s been proved to not be the pump. hmmm … well, the idea to figure out scientifically what system is causing the problem, spark or fuel, that makes a lot of sense. But if you feel lucky, my second guess is that one or more of the injectors are faulty and leaking gas into the cylinders after the engine has been shut off. That would explain why it will start after you wait awhile. That gives the extra gas an opportunity to evaporate. And it would explain the sulfur odor. I presume you live in the eastern part of the USA, which tends to have a little higher sulfur content in the gasoline.
The guy who said that it was the crank shaft position sensor did spray something into (I think he said the air box) and the car started right away but immediately turned off. After that it would start if I let it rest a few minutes between attempts but it always immediately shut off.
It seems that a lot of guessing at the problem has been done but not a lot of good trouble shooting to pin down the problem. You seemed to say that someone sprayed some starter fluid into the intake to see if that helped get the engine running and it got the engine to respond. That is a good easy trick to use when trying to determine if the trouble is fuel or ignition related. If the trouble is fuel related the engine will start and then die shortly afterward as the fluid is used up. The trouble could very well be with the fuel pump relay as others have stated. It sure acts like a faulty relay as intermittent as it is. It is too bad that wasn’t done first instead of replacing the pump. I suggest you try replacing that as a next step. There could also be a faulty power connection beyond the relay but I would say that is a little less likely if the trouble really is with the power to the pump.
Since the "spray fuel into the intake manifold trick "made it start, that would tend to disprove my leaker injector theory. hmm … well, I guess you are back to square one, finding out if it is fuel not spraying when it should, or the spark not sparking when it should. A faulty crank position sensor would prevent spark, and on most cars lack of spark prevent fuel from being injected too. It’s a safety thing. And those CP sensors are known to be heat sensitive. But a faulty fuel pump or fuel pump relay could explain the symptom too. And those parts are also know to be heat sensitive. If I had this problem, when the symptom appeared, I’d make a visual check for spark. Hooking up a fuel pressure gauge would also get to the bottom of it I expect.
I think at this point you have to accept that your car has a problem beyond what a normal mechanic and even an independent BMW specialty shop can handle. That means have the car towed to a BMW dealer. A dealer service department has more diagnostic equipment and might have gone through this scenario before on someone else’s car. I think you have a bad fuel pump, or a bad fuel pressure regulator, or a bad relay in the fuel pump circuit, or a bad ignition switch.
I had a similar problem with my fuel injected marine motor and it was a bad relay.