I doubt it's the fuel pump, try rapping on the MAF with your knuckles. Have a look at the spark plugs. If you want to replace parts then cam sensor would not be a bad idea. The brakes should work like normal at least for the first application when the cars stalls, so something probably going on there. Smoke test doesn't rule out a vacuum leak.

OK I see you replaced the cam sensors, but with OE parts ?? why was the crank sensor replaced ? was that replaced with OE ?? If the problem started after the crank sensor replacement that is highly suspect. Are you reading all the codes with your scanner ??

Especially if the leak is in the booster. Smoke test uses pressure and check valve at booster will block the smoke.

Push your brake before you start the car after sitting a long time even overnight usually will be enough vacuum the pedal is soft.

If you have a firm pedal suggests a leak in booster or the check valve is shot.

Booster leak is a classic diagnostic miss.

If car stalls when going from 5-0 mph it's always been the cam sensor on the cars I've maintained.

I don't usually see stall related to vacuum leak. I usually see plenty of errors if there's a leak or misfire from injectors or plugs.

You mentioned replacing CPS but did you use OEM or better? The engine is really particular on that sensor. New ≠ fixed. Follow the symptoms.


–awr–

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I did not use OEM sensors. I changed the crank sensor bc I incorrectly diagnosed the failing fuel pump. Turned out it was the fuel pump.

I think I'm leaning toward swapping the battery and alternator. Alternator is original. I feel like the car is turning over a touch slower than normal. It's slight, but I know this car and feel it.

Two weeks ago, I drove upstate to fish Salmon on Lake Ontario. Car ran without a hitch. Actually range hit 650 miles with my new fuel filter, oil changed and new cam sensors. I think previously I've only seen Max range at 570 or so. Engine runs smooth. Idle is smooth and steady.

Clean the ICV valve, #1 culprit for stalling.

In my 2004 X3 2.5i, used to have random stalling, cleaned the ICV.
Zero problems since.

While there, change the rubber elbow (BMW part only, no aftermarket.

The smaller rubber bushing for the ICV: you can re-use it.

Good call on the ICV. May cure the problem just cleaning.

+1 on no fake intake boot get a real one. I tried to use a knock off it wasn't corrugated it just had ribs on the outside.


–awr–

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I will try that first. What is the logic on cleaning it vs replacing the ICV. I'll read more about it. I know I've taken it off and checked it over the years. I do not recall replacing it ever, so it's original. My rubber elbow has been replaced, I will check for tears.

Turning over a bit slower is probably the starter. The alternator and battery should be easy enough to test at least to narrow down the slow cranking but also probably not totally waisted money changing if the alternator is original or the battery isn't great.

Regarding the ICV and vac leaks etc. it seems like many of these problems would cause poor running, poor idle, hard starts, bad fuel mileage, etc. I have nothing of that sort. Really seems more like electrical failure of some sort. The car doesn't hesitate and die, it just dies and dash lights come on. Car restarts without issue. Ugh. So frustrating bc feels unsafe driving it.

Get a measurement of the current draw at start. I think the 3.0 pulls about 225 cold start and 175 re-start. I took some voltage drop measurement from the 12v socket to B+ jump point and it worked out to about 1/300 of the current

Eg: .75v drop .75*300=225a

You need a DMM that will register peak DC voltage but that will get you a sense of starter health.

.625*300=187.5 was close to what I would get on an immediate restart. That was with my 3.0.

Most of the cases i read where somebody thinks a bad battery is causing weak starts it's really the starter.


–awr–

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2003 X5 stalled while driving at low speed
 

If the stalls are low speed like stop/go 5-0 mph it's always been the CPS on the cars I've maintained.

If you used a knock off I'd switch it even if that's not the current cause as it's a guarantee to be the problem in the future.

Of a doezen or so CPS I've changed i think only one set an error code related to itself.


–awr–

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