EFI fuel pump query

cappers · Oct 3, 2020

On my previous 3.5 hotwire AFM V8s the fuel pump primed on turning the ignition then switched off and waited for a spark signal before running the pump again after the initial prime.

My conversion doesn't. The pump stays on. Has something been wired incorrectly? Does it matter?

Thanks in advance.

jamesmartin · Oct 3, 2020

should do as you say cut off after 4 seconds till engines turning you normally use the efi loom with the pump relay controlled by ecu, presumably your pumps wired direct bypassing that

Ratae · Oct 4, 2020

Hotwire should do as you say.
The earlier flapper EFi fuel pump ran when the engine was cranking & once the engine fired & the key was released the position of the flap in the AFM kept the pump running.
Handy when checking the fuel system as propping the flap slightly open with the key in the run position powers the pump.

Probably 999/1000 running all the time the key is in the run position wouldn't be a problem, but potential danger in an accident with engine stopped but a severed fuel line as fuel would just keep pumping out.

cappers · Oct 4, 2020

Thanks for the replies.
I checked the two aluminium relays - brown wires to one is power supply for efi, the white/purple wire to second is fuel pump, all wiring seems ok as per manual.
It should work that when the ignition is turned on both should click on then after 4 seconds the fuel relay clicks off until you start the engine.
I hear a click after a few seconds but the pump still runs.
Could it be a faulty relay, stuck on?
Cheers.

jamesmartin · Oct 4, 2020

capo said:
Thanks for the replies.
I checked the two aluminium relays - brown wires to one is power supply for efi, the white/purple wire to second is fuel pump, all wiring seems ok as per manual.
It should work that when the ignition is turned on both should click on then after 4 seconds the fuel relay clicks off until you start the engine.
I hear a click after a few seconds but the pump still runs.
Could it be a faulty relay, stuck on?
Cheers.
View attachment 220533

does the white/purple actually power the pump or is the wire teed too another source

cappers · Oct 4, 2020

jamesmartin said:
does the white/purple actually power the pump or is the wire teed too another source

I'll check tomorrow if it stops raining.

jamesmartin · Oct 4, 2020

capo said:
I'll check tomorrow if it stops raining.

cos it could be relay or relay might be working but theres another pump feed

cappers · Apr 19, 2021

An update 6 months later..... (it's an annoyance rather than a problem)

I changed the fuel pump relay for known good one but still the same, pump runs constantly with no priming step. Furthermore the fuel pump runs even with the fuel pump relay removed

so must have been wired independently of the ECU

Removing the main relay prevents starting.
The main and fuel pump relay wiring doesn't look by the book either.
I need to check that pin 12 (MR) and pin 16 (FPR) aren't earthing somewhere and that pin 19 is getting the ignition pulse via term 86 on the FPR.
If it isn't them it can only be a dodgy ECU or more likely a funky wiring setup. Time to get out the probe

I'll post when I find out more.

cappers · May 21, 2021

Sorting through some photos of the engine conversion and I found these which show the Disco loom that came with it.

The main and fuel pump relays are there plus another black relay which is wired into them. I assume it's not standard Disco1wiring but no ideas apart from it being a relay for a defunct immobiliser or something? It looks like they wired the lot in without altering the setup.

Curious.

EFI fuel pump query

cappers

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jamesmartin

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Ratae

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cappers

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jamesmartin

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cappers

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jamesmartin

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cappers

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cappers

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