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
Ok
So let me start by explain the wiring you start with and then what you should have after the 'upgrade'
Stock
The ecu sends a negative switch to the stock relay on the bulkhead above the battery.
The relay sends a positive and a negative to the fuel pump in pathetic spec wire.
Fuel pump simply uses these wires.
Upgrade
In the wheel arch you add a relay
Use the positive from the stock relay to switch the new relay on.
Run a new fused positive from the starter motor into the relay in adequate wire. then from the relay to the pump.
Run a new negative direct from chassis to the pump.
Original negative is not used.
its because of the pathetic stock wire to the pump that the wiring upgrade is needed... the ecu sends the switching to the relay and controls the pump in both instances and if you crash and you engine cuts out so does the pump as the ecu knows... if the engine is running so is the pump, there isn't any accident switch off like most production cars.
hope that makes sense.
So let me start by explain the wiring you start with and then what you should have after the 'upgrade'
Stock
The ecu sends a negative switch to the stock relay on the bulkhead above the battery.
The relay sends a positive and a negative to the fuel pump in pathetic spec wire.
Fuel pump simply uses these wires.
Upgrade
In the wheel arch you add a relay
Use the positive from the stock relay to switch the new relay on.
Run a new fused positive from the starter motor into the relay in adequate wire. then from the relay to the pump.
Run a new negative direct from chassis to the pump.
Original negative is not used.
its because of the pathetic stock wire to the pump that the wiring upgrade is needed... the ecu sends the switching to the relay and controls the pump in both instances and if you crash and you engine cuts out so does the pump as the ecu knows... if the engine is running so is the pump, there isn't any accident switch off like most production cars.
hope that makes sense.
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?
ERIKM400 said:
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?
When you say "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" - what connector?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?
Well I've just had a good look at mine and I don't have the relay you're talking about and neither do I have that connector. I think that's the fill plug for the gearbox so maybe it's a level or temp sensor for gearbox fluid but wired how you describe it suggests it's only live when the fuel pump is on??
Is there any other wiring around that connector?
Is there any other wiring around that connector?
Erik: The mysterious sender on the gearbox looks to me like a temperature switch. I am guessing that at some point in your car's life it had a gearbox cooler or there was a plan for one - these are fitted in the wheel arch (not sure which side). Not sure if M400 had these standard?
So the second relay appears to be the switch for the gearbox cooler fan, the sensor in your pictures.
If you have a gearbox cooler - although its obviously not in this wheel arch.. otherwise you would see it - then you can energise the relay and check it works (wherever the fan is!). If your car doesn't have a gearbox cooler with a fan (as I suspect) then you can just leave it as-is, tape up any loose ends, etc... for when you want to fit one (if ever).
So the second relay appears to be the switch for the gearbox cooler fan, the sensor in your pictures.
If you have a gearbox cooler - although its obviously not in this wheel arch.. otherwise you would see it - then you can energise the relay and check it works (wherever the fan is!). If your car doesn't have a gearbox cooler with a fan (as I suspect) then you can just leave it as-is, tape up any loose ends, etc... for when you want to fit one (if ever).
Edited by Evo2aGTO on Monday 28th September 20:43
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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