Date: Mon, 23 Jul 2007 21:57:31 -0700
Reply-To: Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM>
Subject: Re: Is ECU involved in getting power to fuel pump when turning
ignition switch on?
In-Reply-To: <786454.27536.qm@web82715.mail.mud.yahoo.com>
Content-Type: text/plain; charset="us-ascii"
See SDF below -
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
David Kao
Sent: Monday, July 23, 2007 9:42 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Is ECU involved in getting power to fuel pump when turning
ignition switch on?
If you look at the fuel pump relay circuit you may wonder why the fuel
pump relay gets power from the #15 terminal of the ignition coil.
This terminal does not have +12V there. The #1 and #15 terminals are
the two leads of the primary winding of the ignition coil. The #1 pin
is connexted to ECU.
I believe the ECU feeds the #1 terminal with the pulsation current, which
makes the high voltage winding to generate high voltage for the spark plugs.
This pulsation current then comes out of terminal #15 to feed to the fuel
pump relay as the power source for the relay.
If for any reason the engine stops (misfires permanently) wheile you are
driving the van, the Hall sending unit will stop generating the Hall signal.
The ECU will stop feeding the pulsation current as a result. Consequently
the fuel pump relay will lose its power from the #15 terminal. As a result
the relay deactivates and the fuel pump stops. This is indeed a safty
feature.
You don't want the fuel pump continues to pump causing fuel line to burst.
As an example, if your van is rear ended by someone, which knocks out the
ignition distributor and the engine stops. Let's say you pass out from the
impact from the rear. So the ighition key is still in the on position.
The fuel pump will stop pumping gas, which may prevent a fire or an
explosion
as a result. Basically if the engine stops the fuel pump will not pump.
When the engine is being cranked the fuel pump will pump because the engine
is turning.
SDF - no, the fuel pump runs during cranking because of the 'start signal'
from the key. It's a black/red wire in the black junction box. After
'start' ..when the engine is running....yes, then it gets the 'keep the fuel
pump relay energized' information from the ignition system.
I believe this to be correct.
If you have a bad ignition coil the fuel pump will not pump. If you have a
bad
Hall sending unit the pump will not pump either. If the ECU is bad of course
the pump may not pump either. I would check the Hall sending unit first.
Usually
the only way it will break down is bad connection. I would check the
ignition
coil's primary winding. ECU is possible so it would be nice if you have a
spare.
SDF - for whatever it's worth......in thousands of vanagons I worked on, I
have never ONCE found a bad hall sensor. I know everybody goes checking for
that cause it's in the Bentley ....I never even think about it, never find a
bad one etc. I have all these parts for sale, good used, of course.
Hope this makes some sense to you.
David
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