Fuel pump problem.

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stevem_it - 08 Jan 2007 13:29 GMT

Hi Porscheheads,

I have an 84 2.5 LUX.
The other day I had difficulty starting it and then while driving it showed
all the symptoms of low fuel pressure. Cutting out under acceleration etc.

I noticed that it had developed a small leak from the pipe leaving the pump.
I have changed the pipe, but now the pump does not appear to run. I have
bridged the relay but the pump does not run when the ignition is turned on
but it does kick when I turn the ignition off.
I have removed the pump and wired directly onto a battery and the pump seem
to run ok.
I have changed the relay, just in case but no luck in getting the pump to
run normally.

Is this pump knackered, even though it works if wired directly to a battery?

Cheers
Steve

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stevem_it - 08 Jan 2007 15:17 GMT

Addendum.

Due to age and stupidity, I jumped the wrong terminals at the relay.
When I jumped the correct terminals, the pump runs continuously. As I think
it should. So the pump appears OK.
So where else should I look now.

I replaced the relay with a new one but the pump does not run without the
jumper.

Cheers
Steve

> Hi Porscheheads,
>
[quoted text clipped - 18 lines]
> Cheers
> Steve

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BGMedia - 08 Jan 2007 19:43 GMT

I have been fortunate and not had fuel delivery problems, so I can't
really give you good advice... but I'll suggest checking your ignition
switch -- especially if you have a large/heavy key fob. I've seen
ignition switches die on other cars and cause wierd problems.

If you're handy with a multimeter, you can download the wiring diagram
and make sure the correct voltages are going to the fuse/relay block.

Good luck!

> Addendum.
>
[quoted text clipped - 31 lines]
> > Cheers
> > Steve

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darthpup - 08 Jan 2007 19:58 GMT

I had a similiar problem with 84 944. I ended up isolating the problem
in the wiring on the relay panel. After twenty years the friction
blade connectors corrode and come loose. Try jiggling the wiring mass
behind relay panel. You will evenually have to remove the seat, get on
your back and press the connections back into place. Spray the whole
mess with ACF50 to revitalize the connections. And it could also be
the ignition switch.

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BGMedia - 09 Jan 2007 01:34 GMT

If you have to mess with all of those connections, wouldn't it be
easier to undo the corner screws on the fuse block and lift it up from
the engine compartment?

> I had a similiar problem with 84 944. I ended up isolating the problem
> in the wiring on the relay panel. After twenty years the friction
[quoted text clipped - 3 lines]
> mess with ACF50 to revitalize the connections. And it could also be
> the ignition switch.

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Martin² - 09 Jan 2007 02:13 GMT

Steve:

>I replaced the relay with a new one but the pump does not run without the
>jumper.

The relay is triggered by the ECU grounding pin 85 of the relay WHEN the
engine is cranking.
Seems to me that's not happening on your car, hence the relay doesn't switch
on the pump.
Either you have bad connection between the ECU and pin 85 of the relay, or
the ECU doesn't
ground it when it detects the engine spinning or maybe the flywheel sensor
doesn't detect the movement (could be just dirty).

On my 868 the ECU has burn out a transistor and doesn't ground pin 85. I
have simply wired pins 87 and 87b to the auto tranny fuse
which gets switched on with ignition, even though mine is manual.

PS I am not familiar with early 944's but I think they all use this std,
Bosch setup and pin numbering system.
Regards,
Martin

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William Noble - 09 Jan 2007 07:13 GMT

you may find it helpful to locate and download the Porsche shop manual - it
has a good diagnostic chart covering this type of problem

> Addendum.
>
[quoted text clipped - 31 lines]
>> Cheers
>> Steve

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