Date:         Mon, 23 Jul 2007 21:02:09 -0700
Reply-To:     David Kao <dtkao0205@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Kao <dtkao0205@YAHOO.COM>
Subject:      Re: Is ECU involved in getting power to fuel pump when turning
              ignition switch on?
Comments: To: most david <dmost@yahoo.com>
In-Reply-To:  <394972.55364.qm@web35601.mail.mud.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

I printed out the circuit diagram from the shop training manual from Benney's
email then did a detail comparison with the circuit for my 84 in mey Bentley
manul. Believe it or not, they are just about the same. The shop manual does
not include a complete circuit so I can't be 100% sure but the fuel pump relay
circuit looks identical.

The ECU's #3 pin does control the fuel pump relay's activation or deactivation
by ground the relay coil's one of the two pins. This is the same to 84's fuel
pump relay circuit.

When the relay is activated the fuel pump should get +12V power through the relay
and should pump fuel. The starter terminal is permanently connected to the battery's
+12V on my 84's circuit. The circuit on the training manual only shows that it is
connectws to starter terminal. So the fuel pump relay circuit for 87 and 84 looks
really the same to me.

Based on this you can conclude that the ECU does control the activation and
deactivation of fuel pump relay. The fuel pump relay gets power from ignition coil
terminal #15. So the ignition module is also responbible for the activation and
deactivation of the pump relay. THe ignition module is controlled by the Hall sending
unit as well as ECU.

I would try to replace ECU, Idle stablization control unit, Hall sending unit,
ignition coil, fuel pump relay and fuel pump. One of them is defective. If you have
the skill of tracing electric signals you can troubleshoot the circuit to identify
the cause of defect. But if you have spare parts it won't take too long to find the
defective part by swapping one of them at a time.

David










--- most david <dmost@yahoo.com> wrote:

> Hi David.  Thanks for the reply.  I now understand that the ECU provides a ground for the fuel
> pump relay.  I'm still trying to figure out what to check next (see my prior email), but I'm
> making progress.
>
> Thanks,
> David
>
> ----- Original Message ----
> From: David Kao <dtkao0205@yahoo.com>
> To: most david <dmost@YAHOO.COM>; vanagon@GERRY.VANAGON.COM
> Sent: Monday, July 23, 2007 4:23:57 PM
> Subject: Re: Is ECU involved in getting power to fuel pump when turning ignition switch on?
>
>
> The answer would be yes for my 84 according to my Bentley. But yours is a 87.
> So I will let others to clarify that for you. I do not have a Bentley manual
> that covers 87.
>
> David
>
>
> --- most david <dmost@YAHOO.COM> wrote:
>
> > It's been one month, and I've made no real progress in solving my "intermittent power at fuel
> > pump when turning key on" problem in my '87.
> >
> > At least one person has suggested the ECU (I've ruled out fuel pump relay and ignition
> switch).
> >
> > For those of you who are good at reading the circuit diagrams in the Bentley, can anyone tell
> me
> > with certainty if the ECU is involved in getting power to the fuel pump when the key is turned
> > to the on (not start) position?
> >
> > Since I can't use the vanagon now due to not being able to count on it starting, I appreciate
> > any help that anyone can offer.
> >
> > Thanks,
> > David
> >
> >
> >
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>
>
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