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.
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).
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
I've also been researching and found this diagram which I am struggling to decipher.
http://www.tom-seven.stillgame.ch/Main/Fuel_pump_l...
Not sure if it helps?
http://www.tom-seven.stillgame.ch/Main/Fuel_pump_l...
Not sure if it helps?
DCL thanks for all the info much appreciated. I have just been to the garage and put the plug back together, the pump is still coming on with the master cut off switched on. I am assuming now the diode is bust so will source another one. Hopefully that solves it.
As an aside having just been out there to check there is a significant (circa 2-3 second) pause before the pump turns on after switching the master cut off on. However when the ignition is switched off there is no pause the pump just runs straight away! So I am assuming that relay closes after the power is initially supplied to the circuit and then remains closed (only interrupted by the ignition and immobiliser). This could potentially point to the diode being unserviceable as I would assume that it should stop the initial signal from the battery (post making the master cut off ON).
Not sure what your thoughts are on my simplified thought process?
As an aside having just been out there to check there is a significant (circa 2-3 second) pause before the pump turns on after switching the master cut off on. However when the ignition is switched off there is no pause the pump just runs straight away! So I am assuming that relay closes after the power is initially supplied to the circuit and then remains closed (only interrupted by the ignition and immobiliser). This could potentially point to the diode being unserviceable as I would assume that it should stop the initial signal from the battery (post making the master cut off ON).
Not sure what your thoughts are on my simplified thought process?
Penelope thanks for all the help sorry in my delayed reply been working nights. I’ve checked all the fuses that I think could be related and they are fine.
The only thing I fiddled with was the plastic connector and diode, the MFRU could have been damaged by my actions I suppose although it seems to be functioning and I can here the relay making initially when the master cut off is supplied.
I will check to see of the pump works with the ECU unplugged but I am 99% confident it will not run. The ecu is an MBE type standard Caterham fit.
I have some new diodes in the post and am hoping this will cure it, I have been unable to test the current one as I don’t have the right equipment. I believe it should be installed as DCL mentioned with the silver band toward the wire going into the MFRU, but I have tried it in both directions and it makes no difference. My hopeful belief is that it’s failed short and is now just acting as a wire.
The only thing I fiddled with was the plastic connector and diode, the MFRU could have been damaged by my actions I suppose although it seems to be functioning and I can here the relay making initially when the master cut off is supplied.
I will check to see of the pump works with the ECU unplugged but I am 99% confident it will not run. The ecu is an MBE type standard Caterham fit.
I have some new diodes in the post and am hoping this will cure it, I have been unable to test the current one as I don’t have the right equipment. I believe it should be installed as DCL mentioned with the silver band toward the wire going into the MFRU, but I have tried it in both directions and it makes no difference. My hopeful belief is that it’s failed short and is now just acting as a wire.
Penelope you are probably right to be honest, my knowledge of the circuitry is limited.
In good news I have just fitted a new diode and it has cured the problem so I must have damaged the last one when removing it.
Big thanks to DCL and Penelope for helping me out with this one and saving some cash (£2 for 10 diodes was the total cost), if you are in or visiting the Reading area anytime send me a message I owe you both a beer.
In good news I have just fitted a new diode and it has cured the problem so I must have damaged the last one when removing it.
Big thanks to DCL and Penelope for helping me out with this one and saving some cash (£2 for 10 diodes was the total cost), if you are in or visiting the Reading area anytime send me a message I owe you both a beer.
Not sure on that one. If you haven’t tried it may be worth disconnecting the battery which will reset the ECU and then trying to start and see how it runs (if you have a battery cut off then this does the same job in which class you’ve probably already tried it). Other potential I can think off could be the lambda sensor in the exhaust (not sure if the 1.6 has one) giving dodgy readings to the ECU.
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