Problems with starting the fuel pump

vendimoto55 · Tue May 21, 2024 11:34 am

Greetings to everybody,

I am writing on behalf of a buddy who has been experiencing difficulties starting the engine of his E46 330D touring vehicle.

Firstly, does anybody own any hyperlinks to wiring diagrams for this particular vehicle? Since I am encountering difficulties in locating anything.

The signal wire connects the fuel pump to the fuel pump. Should this be linked to the ground (disconnected from the gasoline pump) in order to maintain continuity? with my perspective, the answer would be no, but, peculiar occurrences tend to take place with German automobiles. (This persistent short is consistently present and does not go)

We believe we have verified the functionality of the relay by testing it in a different location, and we have also established that the fuel pump is operational when supplied with 12 volts. However, there seems to be an anomalous electrical issue that requires more investigation. Therefore, the electrical connection extends from fuse 54, which is specifically designated for the fuel pump relay, to the relay itself. This wire exhibits an intermittent electrical connection to the ground, which is not consistently present throughout testing. It is possible that this issue is related to manipulating the relay connector and its associated wires. When the relay and fuse are both removed, there should theoretically be no electrical connection to the ground. However, in certain cases, there is still continuity seen. Unclear. Curious to know, I decided to test whether the automobile would start after the short circuit was resolved, and to my astonishment, it did. I am uncertain if this is a deliberate distraction or not. However, the relay seems to be functioning properly and all the necessary voltages are present on the plug to be sent to the pump. However, the pump did not receive any electrical potential difference.

It would be useful to have wiring schematics since the cable for the signal wire at the relay socket has a different colour compared to the signal wire on the main fuel pump located behind the rear seat. Consequently, I presume that this cable is intended to be connected somewhere prior to reaching the fuel pump. I would really appreciate it if someone could provide me with more information on this matter. Indeed, originally the automobile was experiencing a failure to activate any of the gasoline pumps. However, after tinkering with the wiring, it is again operational.

Any recommendations, whether related to electrical issues or not, would be much appreciated as well! The automobile is now operational, but, I anticipate the recurrence of this issue in the future.

dontito · Tue May 21, 2024 11:34 am

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jameswright77 · Tue May 21, 2024 11:35 am

The supply wire connecting the fuse to the relay contact should not be grounded under any circumstances. The lone grounding point is located on one side of the pump, whereas the dde grounds the coil of the relay in order to activate it.
If there is intermittent grounding on the supply wire, it is likely that there is a chafed area somewhere along the wire. It is peculiar that this issue is not causing the fuse to blow.

vendimoto55 · Tue May 21, 2024 11:36 am

Indeed, I found this aspect perplexing. The area on the circuit where the short occurred is the least probable location for such an event, unless there was an entry of unwanted substances in the relay plug. This could potentially clarify why the fuse did not blow, as the presence of unwanted substances does not always result in fuse failure based on my previous encounters. However, upon inspection, there was no visible evidence of such substances, nor should there be any due to the placement of the relay plug. However, he will certainly resolve this matter if it arises again!

Could you further clarify your definition of the DDE grounds? I get the concept of using a ground to activate a relay. However, I am curious about the source of this ground connection that is used to flip the DDE, as mentioned by you.

Additionally, do you happen to know where I can get electrical schematics for this vehicle? I had similar illustrations, but they only depicted a single gasoline pump.

jameswright77 · Tue May 21, 2024 11:36 am

The DDE (ecu) supplies the ground to the relay coil in order to activate it, since the positive side is powered by the fuse.
The web resources mentioned in the link provided by greasy are the ones I would recommend consulting.

vendimoto55 · Tue May 21, 2024 11:37 am

Indeed, I get the matter now. Thank you!

Considering that we were able to successfully start it, would you say the Engine Control Unit (ECU) or Digital Diesel Electronics (DDE) is functioning properly? If this component was damaged due to overheating, it is reasonable to anticipate that it would not function properly upon startup.

jameswright77 · Tue May 21, 2024 11:38 am

Given that the relay is energised when a fault occurs, and that the positive current to the pump is being grounded, it can be inferred that the DDE is functioning correctly by instructing the relay to operate.
Upon discovering a failure in the 12v wire connected to the pump, it is necessary to conduct a more thorough examination of that wire.