It heats up it dies after 30 min. will not restart until you release pressure and wait for 30 min. had this problem on older with carb. we used to call vapor lock it is acting same but this is fuel injected 3800 series II motor a head scratcher if ever I saw one

As you have eliminated the coil and spark plugs than it is likely fuel-related. Perhaps your fuel line is degraded or your fuel pump is failing. Unfortunately until you either have more sophisticated diagnostic equipment such as DIS or ISTA where are you can look at parameters such as fuel pressure it will be they put up with it until it finally fails kind of scenario. Ione several BMW and have never had that problem without a code. Sorry you're saying that you do not get a check engine light at all?

When it shuts off it is time to check things out. Check fuel pressure on the fuel rail and check for spark at the plugs. If no spark the coils may be bad. As the engine heats up the inside of the coil pack may be seperating or grounding themself out. If fuel pressure is low the fuel pump may be weak and on its way out. This happens to people that run there car untill the fuel light comes on.it is ******* the fuel pump because the fuel it's pumping is what cools it. You can search on google or youtube for what your particular cars fuel pressure should be.

Could be bad coil or crank/cam sensor that only fails as it gets hot. Could also be bad gas cap or fuel pump. Use fuel pressure gauge to see if pressure drops as it dies. If electrical, very hard to tell unless while it fails there is no spark to plugs.

hav u replaced the fuel pump--some cars with old pumps are sensitive to turns--git a fuel pressure test done to confirm

I had a trooper that had the same concern. Turned out to be the ECT sensor.

The battery might be dying in one of the sensors, despite still giving a pressure reading. You can either go to have the sensors tested to check their battery status, or just wait until the sensor that has the dying battery finally gives out and you have it replaced.

Check on frame rail on drivers side, near front of gas tank.

check for 12v constant at your fuel pump if you are not getting that replace your relay.
if you are getting 12 volts at your fuel pump the fuel pump is possible to run tuel it gets warm then shut down to a lower rpm I would then replace the fuel pump

check fuel filter and fuel pump. replace if not functioning.

i bet u hav as many miles on dat cars as a trip to the moon-the trans is old in alot of places-varnish on parts from heat etc-u can get troubleshootin lit in library sec629 chiltons or haynes in discount auto