Help needed, fuel pump
Discussion
Hi guys,
I need some help from the wise people of the Noble Community.
The car left me stranded by the side of the road in the pouring rain last week: fuel pump cut out.
Managed to get it back home with the assistance from a friend who passed by and happened to have a tow bar in the back of his car (merci Maurice).
I had some time to work on the car and try to sort the problem over the weekend.
Here's the situation:
My car is a 2005 M400 which has had a fuel pump upgrade and rewiring done by the previous owner. The fuel pump gets it's power supply from a relay which takes power from the starter solenoid and is switched by the original power supply for the fuel pump as described in the well known wiring upgrade scheme. However, the quality of the cables used for the new wiring was pathetic. Because of this the cables running from the original fuel pump power supply (by the ECU) to the new fuel pump relay (in the wheel arch by the pump) had burned through, probably because they were running very close to the front turbo. This also blew some fuses in the engine bay.
I replaced all the wiring and the fuses and got the engine running again.
So far so good, BUT:
1) In the wheel arch next to the pump there is a second relay and I have no idea what this one does. It is wired like this:
- power supply (30) comes from the starter solenoid the same way as the fuel pump relay.
- switching of the relay (+ or 86) is the + cable from the original power supply for the fuel pump, so the same cable which switches the fuel pump relay.
- the mass cable for the relay (- or 85) is a grey cable which runs to a connector that is on the differential behind the gear box.
- the power output from this relay (87) is a black cable which runs back into the engine compartiment in front of the engine block but for the moment I can not see where it's going or what it's connected to.
At the moment the second relay is disconnected and the engine seems to run fine without it.
Has anyone got any idea what this relay could be doing?
2) When rewiring the pump I noticed that I can not find any safety system installed to cut out the fuel pump in case of an accident or disconnected fuel line, or other problem.
Normally there should be an inertia switch or some other system in the fuel pump wiring cutting out the fuel pump when things go wrong.
Is this something which is programmed into the ECU (which then cuts out the original power output for the fuel pump) or is it simply absent on our cars (which I would find rather worrying)?
Any help would be much appreciated.
Cheers,
Erik
I need some help from the wise people of the Noble Community.
The car left me stranded by the side of the road in the pouring rain last week: fuel pump cut out.
Managed to get it back home with the assistance from a friend who passed by and happened to have a tow bar in the back of his car (merci Maurice).
I had some time to work on the car and try to sort the problem over the weekend.
Here's the situation:
My car is a 2005 M400 which has had a fuel pump upgrade and rewiring done by the previous owner. The fuel pump gets it's power supply from a relay which takes power from the starter solenoid and is switched by the original power supply for the fuel pump as described in the well known wiring upgrade scheme. However, the quality of the cables used for the new wiring was pathetic. Because of this the cables running from the original fuel pump power supply (by the ECU) to the new fuel pump relay (in the wheel arch by the pump) had burned through, probably because they were running very close to the front turbo. This also blew some fuses in the engine bay.
I replaced all the wiring and the fuses and got the engine running again.
So far so good, BUT:
1) In the wheel arch next to the pump there is a second relay and I have no idea what this one does. It is wired like this:
- power supply (30) comes from the starter solenoid the same way as the fuel pump relay.
- switching of the relay (+ or 86) is the + cable from the original power supply for the fuel pump, so the same cable which switches the fuel pump relay.
- the mass cable for the relay (- or 85) is a grey cable which runs to a connector that is on the differential behind the gear box.
- the power output from this relay (87) is a black cable which runs back into the engine compartiment in front of the engine block but for the moment I can not see where it's going or what it's connected to.
At the moment the second relay is disconnected and the engine seems to run fine without it.
Has anyone got any idea what this relay could be doing?
2) When rewiring the pump I noticed that I can not find any safety system installed to cut out the fuel pump in case of an accident or disconnected fuel line, or other problem.
Normally there should be an inertia switch or some other system in the fuel pump wiring cutting out the fuel pump when things go wrong.
Is this something which is programmed into the ECU (which then cuts out the original power output for the fuel pump) or is it simply absent on our cars (which I would find rather worrying)?
Any help would be much appreciated.
Cheers,
Erik
Thanks for the reply.
Makes perfect sense.
But it still does not explain why I've got TWO relays in the wheelarch.
The first one switches the fuel pump and is connected the way you describe.
But I am clueless about the second one with the connection to the gearbox differential (see post above).
As said: the engine runs with this second relay disconnected.
It looks like it was installed afterwards and I can not find anything about it in the US 1 G build manual we all use.
Anyone got an idea?
Makes perfect sense.
But it still does not explain why I've got TWO relays in the wheelarch.
The first one switches the fuel pump and is connected the way you describe.
But I am clueless about the second one with the connection to the gearbox differential (see post above).
As said: the engine runs with this second relay disconnected.
It looks like it was installed afterwards and I can not find anything about it in the US 1 G build manual we all use.
Anyone got an idea?
Hi Jason,
Just had a look and there is an oil cooler in the other wheel arch but it doesn't have a fan.
Been thinking about this connector and guessed it should be either an oil pressure sensor, oil pressure switch or oil temperature sensor.
Your explanation about an oil temperature sensor switching an oil cooler fan seems to make sense.
The car was imported from Kuwait (don't ask ;-) so with the hot climate over there the previous owner may have decided that an extra oil cooler for the gearbox was a good idea.
I will leave the relay disconnected for the moment and drive the car around a bit to see what happens.
Thanks to all of you for the advice so far.
Erik
Just had a look and there is an oil cooler in the other wheel arch but it doesn't have a fan.
Been thinking about this connector and guessed it should be either an oil pressure sensor, oil pressure switch or oil temperature sensor.
Your explanation about an oil temperature sensor switching an oil cooler fan seems to make sense.
The car was imported from Kuwait (don't ask ;-) so with the hot climate over there the previous owner may have decided that an extra oil cooler for the gearbox was a good idea.
I will leave the relay disconnected for the moment and drive the car around a bit to see what happens.
Thanks to all of you for the advice so far.
Erik
andygtt said:
The other one may be for a gearbox cooler pump... If you have an oil feed into the top of the gearbox behind the shifter then this is the case.
Will have a look when I get back home tomorrow.If there is a gearbox cooler pump installed, can you tell me where this would be located in the engine bay?
andygtt said:
I located mine in the side pod were you fuel pump is.... but I have seen them located in many different places, which is why I say to look out for the oil return into the top of the gearbox as thats the same for all cars I have seen.
Just had a look at the car and there is an oil return into the top of the gearbox, which seems aftermaket: see pictures. I can trace the oil lines to an oil cooler situated in the right rear wheel arch but I don't see a pump or ventilator.
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