Fuel pump permanently on
Discussion
Hi all,
I’ve been doing some work on the car this morning and cleaned up and resealed an electrical plug that goes into the relay on the side of the battery (R400 Duratec). That has somehow affected its operation as the fuel pump will no longer turn off it is even on when the ignition is out. Only way to turn off is the battery isolator via the cut off. Any help greatly appreciated (potential earth problem assumed but I didn’t move any connection there). Car runs fine.
I’ve been doing some work on the car this morning and cleaned up and resealed an electrical plug that goes into the relay on the side of the battery (R400 Duratec). That has somehow affected its operation as the fuel pump will no longer turn off it is even on when the ignition is out. Only way to turn off is the battery isolator via the cut off. Any help greatly appreciated (potential earth problem assumed but I didn’t move any connection there). Car runs fine.
Thanks for the reply. Yea as soon as I unplug that connector it will not work at all. The connector is just down from the MRFU and has what looks like a diode in it and that is all. I have since resealed it and put it back but the pump is still continuously on (tried it running both ways). The relay in the MRFU seems to be working just in the wrong way now.
Sequence goes. Cut off key on, pause two seconds pump turns on and starts priming. Ignition on pump cuts out, immobiliser deactivated fuel pump runs again engine starts. Turn ignition off fuel pump cuts out pause two seconds then it starts running again, only way to turn off is cut off key.
My only assumption so far is that the diode is now bust but I have no idea how to get a matching one.
Sequence goes. Cut off key on, pause two seconds pump turns on and starts priming. Ignition on pump cuts out, immobiliser deactivated fuel pump runs again engine starts. Turn ignition off fuel pump cuts out pause two seconds then it starts running again, only way to turn off is cut off key.
My only assumption so far is that the diode is now bust but I have no idea how to get a matching one.
Well at least you have a way of turning it off 
What prompted you to work on it in the first place? What problems was it showing? Had something happened to it before to prompt the work?
Seems like there's something wrong with the connector or the relay unit(s). Maybe a short of some description?
Do you have diagrams of what does what in the MRFU?
What prompted you to work on it in the first place? What problems was it showing? Had something happened to it before to prompt the work?
Seems like there's something wrong with the connector or the relay unit(s). Maybe a short of some description?
Do you have diagrams of what does what in the MRFU?
I stupidly thought it was the spare connection for the oil temp sensor (not fitted to my car, that I was fitting). So I stripped it down and fitted the cable and sensor to check at which point I realised it wasn’t (as the car wouldn’t start). All it had was a plastic connector plug spliced into a green/brown wire with some heat shrink on the end (containing the diode, or what i believe is the diode).
My auto electric knowledge is somewhat limited so although I could find the MRFU diagrams I reckon I would struggle to do anything with them. Suppose my next option is to ring a professional.
My auto electric knowledge is somewhat limited so although I could find the MRFU diagrams I reckon I would struggle to do anything with them. Suppose my next option is to ring a professional.
djwhittaker14 said:
I stupidly thought it was the spare connection for the oil temp sensor (not fitted to my car, that I was fitting). So I stripped it down and fitted the cable and sensor to check at which point I realised it wasn’t (as the car wouldn’t start). All it had was a plastic connector plug spliced into a green/brown wire with some heat shrink on the end (containing the diode, or what i believe is the diode).
My auto electric knowledge is somewhat limited so although I could find the MRFU diagrams I reckon I would struggle to do anything with them. Suppose my next option is to ring a professional.
My auto electric knowledge is somewhat limited so although I could find the MRFU diagrams I reckon I would struggle to do anything with them. Suppose my next option is to ring a professional.
Thanks for the help so far. Hopefully the photos help. You can see the plastic plug and it’s contents must have had some effect but I am unsure how I’ve changed that with my actions. It also feels like it may have been a bodge job by the previous owner which I’ve now uncovered. Either way the symptoms are that the relay is doing the opposite of what it should when battery power is applied (acts normally when ignition is on).
The plug you tried to modify does have a diode and is part of the MFU electronics. I am not sure about it exact function but is likely to be used to interrupt the fuel pump relay as part of the fuel pump control sequence from the ECU. I would suggest it is probably now open circuit and the fuel pump relay is latching on in some way.
Great thanks for that I will give it a shot. Assuming the diode is no longer functional (I don't have an ohm meter) any idea how I get a replacement I've done an online search for the numbers written on the diode but not a lot comes up. I believe it is something along the lines of 1N4001(top line) 0727A (bottom line). Kind Regards, Dan
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