Strange Starting Problem

[1stBMWTom]

Hi all,
I just purchased my first BMW about 6 weeks ago, a used 2006 X5 4.8is that had about 16,700 miles on it.

I've had a weird starting problem occur two times under similar conditions but never at any other time. On both occasions the problem happened after the vehicle had been on an incline or lifted up. Once was after driving up ramps to do an oil change, the other most recent time was after jacking up the rear to put on my winter wheels/tires.

The problem is as follows....when you first turn the ignition key and the engine starts, it barely catches and then barely stays running and idles very low. It almost sounds like it is running on/pinging/dieseling. It's a very disturbing metallic-like sound but is probably just due to the low idle of the engine. When you shut the engine off and try to restart, it has a very difficult time restarting. When it finally does you can definitely smell unburned gas from the exhaust.

This has only happened twice in 6 weeks and both times starting directly after having the vehicle on an incline. Any thoughts?

As an aside, I've been working on all sorts of cars/trucks for about 24 years. I also build and tune high performance engines, so I'm no stranger to working around vehicles. This one certainly seems odd though so I thought I might throw it out here to see if it has happened to anyone else.

Thank you in advance,
Tom

[Weasel]

I can honestly say I've never heard that one before... Can it be duplicated? Would it do it every time it's put on an incline? If it can be easily duplicated I'd be curious of what the fuel pressure does when that happens. It has the same valve stem sized fuel fitting as a ford, on the passengers side fuel rail.

[1stBMWTom]

I guess the first two instances of it happening on an incline were coincidental.

I had it happen tonight after just sitting in the garage for a few hours after getting home from work.

Went to start it, it started and instantly just began to idle at maybe 200-300 rpms with that horrible "knock" type of sound. I shut it down and waited about 10 seconds to turn it over, all it would do is crank but not fire. Let the key go and of course the start assist kept the starter engaged even after I let the key go. I'm wondering if that worthless feature is what is causing the problem in the first place.

Finally started after a few minutes of trying, with lots of wonderful unburned gas aroma to boot. Is there a secret compartment located somewhere in the X5 where this supposed "quality" is hidden? I'm still trying to find it.....