Fuel pump power issue...

JDZ2 · Mar 18, 2020

Hi all,
I have just joined the forum & am hoping for some assistance with my non running, newly acquired Discovery V8i series 1 '93.
It had been recovered & left by the previous owner who had already purchased a new model before the old one let him down
So, vehicle electrics are not my strong suit but I will persevere..
Engine turns over but no fuel. Battery is good. Fuel pump has no power. I have removed the fuel pump to test it & it works OK outside of the vehicle. I have tested 2 relays located under the dash, drivers side to the left of the pedals -they are 5 pin 30amp relays which I have tested on the bench & they both 'click' nicely.
However, in position they don't click, they buzz....& I dont know how to solve this or what would cause this.
Needless to say, I cannot find any power at the fuel pump end...
I have read about an inertia switch but cannot locate it...should there be one?
Any electrical wizards to advise?...thanks....

sierrafery · Mar 18, 2020

Hi. First of all what voltage you have on the battery while cranking? buzzing relay means it gets power but not enough

discool · Mar 18, 2020

Hi JDZ2, first you will have to understand how the 1993 V8s EFI system which is simple, so go for it.
U don’t have a flat battery do u as relays chatter then when cranking, as I find out regularly.

Ok so your engine turns over, but is the a spark at the plugs, the coil supplies HT volts to the dizzy but also it will Pulse to the EFI ECU which controls the fuel pump, if it doesn’t then there could be an issue with the 12v supply to the coil, note your vehicles immobiliser, if fitted, will also indirectly affect the pump.

If u find the is a spark at the plugs while cranking, then to follow circuit (into and out of) the ECU you will need a wiring diagram for your model year of vehicle, and follow the route from the ECU to the pump relay, the the 12v also importantly the relay earth (ground) a nice click from the relay on the bench doesn’t mean it’s fully functioning when installed as u have found out.

If your vehicle is still fitted with a inertial emergency fuel cut off, it will be positioned in the engine bay on the rear bulk head, which is on the near side of a 300 series V8 disco.

JDZ2 · Mar 18, 2020

sierrafery said:
Hi. First of all what voltage you have on the battery while cranking? buzzing relay means it gets power but not enough

Hi,
I don't know what it is whilst cranking, I will try to ascertain that tomorrow, it's dark here now. I did take a reading across the battery terminals when the battery was back in place,
of 12.53 volts. I took the battery off the vehicle yesterday afternoon when I took ownership of the Discovery, had it on charge all night. Whilst it was on the bench, I took the relays off & tested them & they both worked perfectly.

JDZ2 · Mar 18, 2020

discool said:
Hi JDZ2, first you will have to understand how the 1993 V8s EFI system which is simple, so go for it.
U don’t have a flat battery do u as relays chatter then when cranking, as I find out regularly.

Ok so your engine turns over, but is the a spark at the plugs, the coil supplies HT volts to the dizzy but also it will Pulse to the EFI ECU which controls the fuel pump, if it doesn’t then there could be an issue with the 12v supply to the coil, note your vehicles immobiliser, if fitted, will also indirectly affect the pump.

If u find the is a spark at the plugs while cranking, then to follow circuit (into and out of) the ECU you will need a wiring diagram for your model year of vehicle, and follow the route from the ECU to the pump relay, the the 12v also importantly the relay earth (ground) a nice click from the relay on the bench doesn’t mean it’s fully functioning when installed as u have found out.

If your vehicle is still fitted with a inertial emergency fuel cut off, it will be positioned in the engine bay on the rear bulk head, which is on the near side of a 300 series V8 disco.

Hi, thanks for the reply. I will investigate the sparks tomorrow in the daylight. Sadly, I don't have the luxury of a garage. Interesting what you said about the relays, so there is no correlation between on the bench / in position in the car. I have looked for the inertia fuel cut off switch but cannot see it on the bulkhead. There are just several wire plug connectors with worn out labels that I cannot read. I have ordered a Haynes manual which will help; I have no owner's manual, no fusebox or wiring diagram at present so it feels a little blind at this stage. I will keep the thread updated for others to benefit from any useful info.

discool · Mar 18, 2020

JDZ2 said:
Hi, thanks for the reply. I will investigate the sparks tomorrow in the daylight. Sadly, I don't have the luxury of a garage. Interesting what you said about the relays, so there is no correlation between on the bench / in position in the car. I have looked for the inertia fuel cut off switch but cannot see it on the bulkhead. There are just several wire plug connectors with worn out labels that I cannot read. I have ordered a Haynes manual which will help; I have no owner's manual, no fusebox or wiring diagram at present so it feels a little blind at this stage. I will keep the thread updated for others to benefit from any useful info.

The weather should be good tomorrow.
The Haynes will cover both D1s with electrical circuits, although you may have to relate to the 300 series, that’s from 1994 when that model was launched with the 1995 model year.
The Haynes book is designed for the DIY mechanic so a bit better than the D1 factory item that was originally published for the trained mechanic.
The inertia switch is a break switch therefore It would isolate the supply to the pump, if your vehicle had one, to reset it is just a simple press on the top of the switch. I see no reason why the switch would be removed as it sits there asleep until the vehicle is in a crash sufficient to operate it.

I’ve never see an owners hand book for the 200 series, it could very well be a collectors item now, but a copy maybe be available on line, I did once try to get a hand book to get the sequence for setting the manual alarm-immobiliser with a key in the drivers door, but never did.

JDZ2 · Mar 18, 2020

discool said:
The weather should be good tomorrow.
The Haynes will cover both D1s with electrical circuits, although you may have to relate to the 300 series, that’s from 1994 when that model was launched with the 1995 model year.
The Haynes book is designed for the DIY mechanic so a bit better than the D1 factory item that was originally published for the trained mechanic.
The inertia switch is a break switch therefore It would isolate the supply to the pump, if your vehicle had one, to reset it is just a simple press on the top of the switch. I see no reason why the switch would be removed as it sits there asleep until the vehicle is in a crash sufficient to operate it.

I’ve never see an owners hand book for the 200 series, it could very well be a collectors item now, but a copy maybe be available on line, I did once try to get a hand book to get the sequence for setting the manual alarm-immobiliser with a key in the drivers door, but never did.

Does that mean that not all the models would have the inertia switch? I agree, I can't think of a reason to remove it. The previous owner owned it for 23 years, it's 2 previous owners from new & it's in great shape for a 27 year old vehicle; still has the original front & rear number plates with supplying dealer on them & the front & rear bumpers etc all look original, so I think it's unlikely it's been in accident to operate the switch. I will, of course take another look although I confess I don't actually know what one looks like but it should be obvious I think.

discool · Mar 18, 2020

Have look behind the windscreen washer bottle the black round top of the switch that is pressed can be seen and easy to reach and pressed.
Only vehicles with fuel injection (petrol or diesel) plus high pressure electric fuel pumps have the factory fitted switch, so only the petrol engine D1s
See No 3 is similar I believe your model has a black square box with a small button on top to press.

sierrafery · Mar 18, 2020

IMO the gist of the problem is

JDZ2 said:
However, in position they don't click, they buzz

if the inertia switch was tripped the relay was not suppossed to buzz cos it cuts the feed to it's coil

JDZ2 · Mar 19, 2020

sierrafery said:
IMO the gist of the problem is
if the inertia switch was tripped the relay was not suppossed to buzz cos it cuts the feed to it's coil

I'm unclear about what that means...are you meaning the relay shouldn't be buzzing at all therefore it points to something else & not the inertia switch? ( If I can find one)

JDZ2 · Mar 19, 2020

discool said:
Have look behind the windscreen washer bottle the black round top of the switch that is pressed can be seen and easy to reach and pressed.
Only vehicles with fuel injection (petrol or diesel) plus high pressure electric fuel pumps have the factory fitted switch, so only the petrol engine D1s
See No 3 is similar I believe your model has a black square box with a small button on top to press.

Thanks for the diagram, that's a great help.....raining here at present but I'll investigate further this morning if there's a break....

jamesmartin · Mar 19, 2020

JDZ2 said:
I'm unclear about what that means...are you meaning the relay shouldn't be buzzing at all therefore it points to something else & not the inertia switch? ( If I can find one)

when you switch ignition on the relay with the brown thick wire clicks on this switches the other fuel pump relay on for 4 seconds,it then shut fuel pump off till ecu sees engine is cranking which it knows from a wire feed from the coil it can sense the pulse, if your relays are buzzing they are either faulty or not getting enough power, inertia switch would cut power completely so no buzzing, they are 30 amp relays so you need to get like for like and not just any 5 pin relay

JDZ2 · Mar 19, 2020

jamesmartin said:
when you switch ignition on the relay with the brown thick wire clicks on this switches the other fuel pump relay on for 4 seconds,it then shut fuel pump off till ecu sees engine is cranking which it knows from a wire feed from the coil it can sense the pulse, if your relays are buzzing they are either faulty or not getting enough power, inertia switch would cut power completely so no buzzing, they are 30 amp relays so you need to get like for like and not just any 5 pin relay

Hi, thanks for the advice. You may have noticed my previous posts on here...so, I bench tested the relays & purchased 2 new ones because I had convinced myself they were faulty before I tested them. Iv'e been told that bench testing them doesn't mean they are OK. The old relays are metal cased Bosch, the new are from Halfords, plastic cased & the bodies slightly bigger but they are the same: pin no's match, 30 amp 12v. I have looked again & cannot identify the inertia switch so at this stage I still don't know if there is one at all regardless.
So, it's unlikely all 4 relays are faulty, right? Then, where should I look next? The coil? Why would the relays not be getting enough power?

sierrafery · Mar 19, 2020

JDZ2 said:
I'm unclear about what that means...are you meaning the relay shouldn't be buzzing at all therefore it points to something else & not the inertia switch?

YES

...

JDZ2 said:
So, it's unlikely all 4 relays are faulty, right? Then, where should I look next? The coil? Why would the relays not be getting enough power?

Follow the black wire which should go to an earth point or splice into that wire with one connected to a ''solid" earth to rule that out, eventually measure voltage on the relay's coil in situ with ignition on cos if it's buzzing there should be some volage but not enough to close the contact which means bad earth or a voltage drop on the feed path. If across the coil the voltage is low measure across body and the coil's positive side and if you get good voltage then the earth to the relay is bad

JDZ2 · Mar 19, 2020

sierrafery said:
YES

...
Follow the black wire which should go to an earth point or splice into that wire with one connected to a ''solid" earth to rule that out, eventually measure voltage on the relay's coil in situ with ignition on cos if it's buzzing there should be some volage but enough to close the contact which means bad earth or a voltage drop on the feed path. If across the coil the voltage is low measure across body and the coil's positive side and if you get good voltage then the earth to the relay is bad

Many thanks, that's great advice...I'll get out there when the rain stops!

jamesmartin · Mar 19, 2020

JDZ2 said:
Hi, thanks for the advice. You may have noticed my previous posts on here...so, I bench tested the relays & purchased 2 new ones because I had convinced myself they were faulty before I tested them. Iv'e been told that bench testing them doesn't mean they are OK. The old relays are metal cased Bosch, the new are from Halfords, plastic cased & the bodies slightly bigger but they are the same: pin no's match, 30 amp 12v. I have looked again & cannot identify the inertia switch so at this stage I still don't know if there is one at all regardless.
So, it's unlikely all 4 relays are faulty, right? Then, where should I look next? The coil? Why would the relays not be getting enough power?

if they are buzzing before cranking ie with ignition on its not relays or inertia switch its insufficient power to relays or poor earth to relays

JDZ2 · Mar 19, 2020

OK.....thus far:

I have a spark...great.
The relays.....when the ignition is on: neither relay makes a sound, when cranking neither relay makes a sound. When I turn the ignition back to position 1, the relay with the
blue plug does nothing, the other relay buzzes. I'm now trying to follow/trace the wire from the blue relay plug pin no 85. Does this extra info give any insight to anyone?

JDZ2 · Mar 19, 2020

..I should of said added: pin no 85 I think is the earth cable.
Please note, I have no wiring diagram or anything to reference to hand!

jamesmartin · Mar 19, 2020

any pics of both relays and surrounding area

JDZ2 · Mar 19, 2020

jamesmartin said:
any pics of both relays and surrounding area

Fuel pump power issue...

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