This is on a 1984 BMW 6 series but people on BMW forums know jack crap when it comes to their own cars, so I figured it would do more justice here. This system is your standard return-style fuel system, regulator on the fuel rail, a single in-line fuel pump and a draw pump in the fuel tank. Nothing fancy, still has a MAF, 6 injectors and a computer to run it all. Let me know if you guys have any suggestions.

Alright, this is my second brand new Bosch pusher pump I've installed, I put only one new in-tank fuel pump in, I've done the fuel filter twice and just installed a new fuel pressure regulator.

Here's the problem, when the engine is stone cold, it will run fine and it will redline (getting pissed, so I tried it). When the engine gets warmer and warmer it just will NOT maintain fuel pressure like it should. The longer I drive it, the worse it gets. It will idle normally at 30psi but when you press on the gas, fuel pressure creeps further down the higher up the RPMs get. Here's the weird part though.

I put it in park and I floor it, it will free rev to around 4500rpm until fuel pressure reaches say, 10psi, then it will just fall HARD while free revving. If I keep the fuel pedal to the floor, the engine will hover while sputtering and backfiring at 2500ish rpm. BUT, if I only do partial throttle, I can free rev all the way to redline and fuel pressure will maintain 20-25psi while I do so.

I'm just lost at this point, any advice would be great. Thanks!

P.S.
The ONLY two things I can think of is either:
A. The in-tank pump is going bad and slowing down as it gets warmer, causing a restriction in fuel flow (which really shouldn't be to THIS extent though).
B. Either the MAF or Computer is bad, when it gets warm, or when the IAT goes up, it's causing the injectors to run at 100% duty cycle, thus flooding the engine while dropping fuel pressure.

 

No clue, (no experience with beemers) but I would expect a fuel pump to be able to outrun open injectors.

Is there a sensor that could be misinforming the engine control computer in a way that causes it to think the engine is not running, thereby shutting down the fuel pump?

 

Ehhhh, I doubt this system is that in depth. Really, the in-tank fuel pump shouldn't be a restriction, but right now that's really my best guess of what's happening, because I do agree with you that open injectors shouldn't drop fuel pressure like that.

 

So, if you've got time to kill experimenting...

Is the fuel return accomplished by a vacuum line to bypass diaghragm? If so, remove and plug the line, preferably with a vacuum guage. Should read high at idle (low fuel demand), and drop with throttle applied. Also, tap a voltmeter into the power feed to the pump. Run your test again. I still think it's a problem with a sensor or ported vascuum since the problem only occurs on a warm engine (closed loop operation). During cold (open loop) operation, the ECU will ignore some sensor inputs and rely on a base map of operating parameters. Good luck.