Fuel pump power issue...

JDZ2 · Mar 20, 2020

discool said:
Considering all that cranking and not firing I would expect that the plugs to be soaking wet, if so there’s not much hope of starting, there’s a fuel pressure valve on the injector fuel rail or slacken an injector hose to check petrol is reaching the engine.

OK, yup, will do....thanks.

sierrafery · Mar 20, 2020

Dont kill the battery again cos i won't start as long as the other(main) relay is not closed(it seems that the ECU refuses to deliver earth to both relay's coils), beside what @discool said try to give direct earth to pin 85(blue/purple wire) of the pump relay and to pin 86(blue/red wire) of the main relay then try or if it's easyer bridge the main relay too for test to see if it starts then with both relays bridged

JDZ2 · Mar 20, 2020

JDZ2 said:
OK, yup, will do....thanks.

...checked all the plugs whilst waiting for the battery to charge up. The plugs were a little sooted up but completely dry....

JDZ2 · Mar 20, 2020

OK, still no attempt to fire at all.
I have removed removed the fuel line into fuel pressure regulator & there is fuel there so that's good. I can see very minor dampness in the pipe unions on the fuel pump so that's good & I will tighten them further. With the relays jumped as suggested I can hear the pump motor whirring. I have checked the plugs again & they are still dry & clean. So with the refreshed battery I'm cranking the engine, it's turning well but absolutely no attempt to fire!!
Any thoughts on what I should try next? Perhaps something silly or minor?

sierrafery · Mar 20, 2020

At this point seems that the ECU is not managing the injectors so not so minor IMO... are you sure that the ECU has feed cos it should close those relays you bridged and manage the injectors too and it seems it doesnt do it's job at all

JDZ2 · Mar 20, 2020

sierrafery said:
At this point seems that the ECU is not managing the injectors so not so minor IMO... are you sure that the ECU has feed cos it should close those relays you bridged and manage the injectors too and it seems it doesnt do it's job at all

No, I don't know if it does, I will see if I can find out....thanks.

sierrafery · Mar 20, 2020

Unfortunately i dont have pre-95 diagrams so i can't tell you where to measure but IMO you should make sure that the ECU is ''active'' cos it seems very like it's not doing anything

discool · Mar 20, 2020

First make sure the two coil top terminals & connections are clean and tight, the black/white from the coil negative terminal links directly to the ECU and carries the pulse signal to the ECU when the engine is cranking & running. No link, no EFI function.

JDZ2 · Mar 20, 2020

discool said:
First make sure the two coil top terminals & connections are clean and tight, the black/white from the coil negative terminal links directly to the ECU and carries the pulse signal to the ECU when the engine is cranking & running. No link, no EFI function.

OK thanks, I'm cleaning all the connections now. There is also 1 little cylindrical component attached to the body by the coil - is it a capacitor? Anyhow, there is a wire connected to it with a double spade connector...it's loose, not connected to anything & I don't know which terminal it should go to?

Stanleysteamer · Mar 20, 2020

Is there any mileage in OP taking an injector off and earthing it, then cranking to see if anything actually sprays out? Bit old school and only to be done safely, but wouldn't that eliminate or confirm the ECU problem?

JDZ2 · Mar 20, 2020

OK, it's a noise suppressor onto the positive side....found it.

discool · Mar 20, 2020

JDZ2 said:
OK, it's a noise suppressor onto the positive side....found it.

Interference suppressor then

in the wiring diagram previously posted u will see that the ECU has three earth connections, they will terminate local to the ECU later D1s the earth point is a stud worth checking.
There isn’t a DIY diagnosis of the ECU function unfortunately, so replacing with a known working one Is the only other DIY option.

I went through an ECU issues many years ago, the only way my main dealer could check was by replacement taken from another RR, but they weren’t able to supply a new one, there was a national shortage, but at least it was drivable... just.
I had to remove the ECU and take it the the Lucas department that dealt with LR ECUs, so off I went to Litchfield 200+ mile return in a fast car

Lucas put my ECU on a gig and after 90k miles not surprisingly found loads of faults, they then replace components while I waited, and updated the ECU. When fitted back in the RR the engine roared was better than ever.
That was for a 3.5 engine not a 3.9 that u have.

jamesmartin · Mar 20, 2020

JDZ2 said:
OK, still no attempt to fire at all.
I have removed removed the fuel line into fuel pressure regulator & there is fuel there so that's good. I can see very minor dampness in the pipe unions on the fuel pump so that's good & I will tighten them further. With the relays jumped as suggested I can hear the pump motor whirring. I have checked the plugs again & they are still dry & clean. So with the refreshed battery I'm cranking the engine, it's turning well but absolutely no attempt to fire!!
Any thoughts on what I should try next? Perhaps something silly or minor?

just getting the pump running wont sort out why the relays dont work properly black one needs to switch ecu on which then switchs fuel pump relay on, without black relay working it wont run

JDZ2 · Mar 20, 2020

discool said:
Interference suppressor then in the wiring diagram previously posted u will see that the ECU has three earth connections, they will terminate local to the ECU later D1s the earth point is a stud worth checking.
There isn’t a DIY diagnosis of the ECU function unfortunately, so replacing with a known working one Is the only other DIY option.

I went through an ECU issues many years ago, the only way my main dealer could check was by replacement taken from another RR, but they weren’t able to supply a new one, there was a national shortage, but at least it was drivable... just.
I had to remove the ECU and take it the the Lucas department that dealt with LR ECUs, so off I went to Litchfield 200+ mile return in a fast car
Lucas put my ECU on a gig and after 90k miles not surprisingly found loads of faults, they then replace components while I waited, and updated the ECU. When fitted back in the RR the engine roared was better than ever.
That was for a 3.5 engine not a 3.9 that u have.

That was for a 3.5 engine not a 3.9 that u have.....
Mine is a 3.5 not a 3.9...

JDZ2 · Mar 20, 2020

black one needs to switch ecu on...
So the black relay turns the ecu on? Then the ecu is off & is why the fuel injection is not working.
I need a better understanding of vehicle electrics...other than changing the relay itself, I need to work out how to solve the issue with the plug then...

JDZ2 · Mar 20, 2020

However, in position they don't click, they buzz....& I dont know how to solve this or what would cause this.......is what I wrote in my original / first post.
So this appears to be the nub of the problem....does anyone have any suggestions as to where I may look to solve this?

jamesmartin · Mar 20, 2020

JDZ2 said:
However, in position they don't click, they buzz....& I dont know how to solve this or what would cause this.......is what I wrote in my original / first post.
So this appears to be the nub of the problem....does anyone have any suggestions as to where I may look to solve this?

what were the original relays like

sierrafery · Mar 20, 2020

JDZ2 said:
However, in position they don't click, they buzz....& I dont know how to solve this or what would cause this.......is what I wrote in my original / first post.
So this appears to be the nub of the problem....does anyone have any suggestions as to where I may look to solve this?

This was answered then... measure voltage across the coil with relay in situ

JDZ2 · Mar 20, 2020

The originals were Bosch, slightly smaller than the recent ones, grey metal cased...here's a picture

JDZ2 · Mar 20, 2020

sierrafery said:
This was answered then... measure voltage across the coil with relay in situ

Darn it, I must have missed that, I haven't done that yet. If the reading is bad it means a new coil?

Fuel pump power issue...

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