[928uk] Fuel pump over-running on ignition

[Paul]

Unlike some other cars, the 928 pump does not prime the ignition when
switching on the ignition

It only runs when the Crank Position Sensor says the engine in turning over
(either via starter motor or by itself)

This means you need more juice left in a failing battery than you would if
it primed the system for a 2 or 3 seconds each time you switch on the
ignition

A strange oversight

Paul
87 S4 Manual

On Fri, 28 Jun 2019 at 15:25, Paul Lacey via 928uk <928uk at lists.928.org.uk>
wrote:

> No it runs all the time
>
> Best Regards,
> Paul L
>
>
> On Friday, 28 June 2019, 15:21:30 BST, David Martin <3admartin at gmail.com>
> wrote:
>
>
> It only runs whilst the ignition is on... but I was sure that it ran and
> then switched off when the system was pressurised......
>
>
>
> On Fri, Jun 28, 2019 at 3:16 PM Paul Lacey <t595 at btopenworld.com> wrote:
>
> Hi,
> The fuel pump does run all the time, excess fuel returns to the tank, fuel
> pressure regulator maintains correct pressure inside the injector supply
> rails.
> The pump runs when it's relay is energised. The ECU tells the relay when
> to be on and this is when engine is cranking, and all the time the engine
> is running.
> So if your fuel pump is running with engine off then either your pump
> relay has been bypassed, or jumpered somehow, or the relay has got jammed
> closed (that'll be a first I've heard of). Try another relay like front
> fogs etc.
> It's nothing to do with ignition switch.
>
> Best Regards,
> Paul L
>
>
> On Friday, 28 June 2019, 15:08:43 BST, David Martin via 928uk <
> 928uk at lists.928.org.uk> wrote:
>
>
> Hi,
> Latest little foible is that when I turn on the ignition, the fuel pump
> fires up and starts priming but doesn't stop it just keeps running.... Any
> thoughts on previous experience of this and likely cause would be very
> useful.... Top options are:
> Fuel Pump shorting on ignition
> Relay fixed on
> Fuel pump broken
> Fuel filter - but not sure what that could be doing
>
> The last one I was going to add was fuel pressure sensor but not sure
> there is one unless its in the fuel pump itself....
>
> Thanks all
>
> David
> 1984 928 S2 Manual
>
>
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