The 2001 BMW 525d e39 with the M57 engine is experiencing difficulties starting due to insufficient rail pressure.

[CyberNinja]

Hello.

I am experiencing difficulties initiating the ignition of my engine. The engine was suspended on a stand for a considerable period of time until I fitted it. During the first startup, I used a significant amount of initial fuel, which resulted in the engine igniting and running smoothly. Subsequently, it became effortless to start the engine. When rewiring the system once again, as I had previously sketched it temporarily while activating it, I had the same issue of difficulty starting it. Although it started successfully with the assistance of gas, it required gas for every subsequent start. Currently, it is not able to start or ignite.

Thus concludes the narrative of the issue, and now we will go to the subsequent aspect. The current issue involves an engine swap in an older Volvo 745, where a stand-alone Engine Control Unit (ECU) has been installed. When using INPA, no "valid" fault code is displayed to indicate the specific problem. However, it is observed that the rail pressure is significantly low. During the initial cranking, the pressure rises to 60 bar, but subsequently drops rapidly to 10 bar. I am now use two pumps to maintain the pressure in the low-pressure line, with one pump located within the fuel tank and the other positioned under the vehicle. The gasoline filter was changed during the installation of the engine.

According to INPA, the pre-pressure is 3.81 while the gasoline pumps are functioning. while cranking, the figure declines rapidly. Is this considered normal?
Furthermore, I attempted to substitute the o-ring on the fuel pressure regulator. Although it seemed to be in good condition, I decided to replace it while it was detached. However, this replacement did not provide any noticeable changes.
Based on my observation, there are no air bubbles present in the fuel line, both before and after starting the engine.

I have been contemplating if the rail pressure sensor may be responsible for displaying inaccurate pressure readings, but I am unsure of how to measure it.
Is it possible that the boost sensor on the intake might potentially contribute to some of the issues?

Sincerely

[bvlenci]

Can you provide a description of the injectors?

[CyberNinja]

I believe they are satisfactory, but I am uncertain. The donor vehicle originated from Germany, and I myself transported it by backpacking and driving it back to my destination. I never had any issues while the e39 was still in use. I like to recall that the vehicle had around 300,000 km on its odometer.

To properly inspect the injectors, it is necessary to have the engine running and measure the return feed from each injector, correct?

[bvlenci]

Indeed, doing a leak off test would be a prudent first step.
Measure the returns from the injectors while the engine is operating.

[CyberNinja]

Understood, I will verify if I can locate any resources for the examination.

Is it typical for the pre-supply feed pressure to decrease from 3.8 bar to 1 bar during cranking?

[CyberNinja]

The issue has been resolved. The issue was not caused by the injectors, but rather by my ignition key. When the key was turned to the "crank" position, it interrupted the flow of electricity to the ECU at pin 26.
I identified the issue when I connected the fuel pump relay and saw that INPA disconnected when I attempted to start the engine for more than 5-6 seconds. Consequently, I discovered that the relay disengaged during the starting process.

Thank you for your assistance! I will inspect the injectors at some point in the future. The only reason for not completing the task today was due to my forgetfulness in bringing the appropriate measuring cups.

[bvlenci]

I am pleased that you have identified the issue.