Date: Thu, 26 Jul 2007 11:20:38 -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: <BAY125-F212452583011E15EE90A43A0F20@phx.gbl>
Content-Type: text/plain; charset="us-ascii"
Hi.
I've heard that electricity 'actually' flows from negative to positive all
right, but in practice it is considered to flow, DC is, from positive to
negative. That's why ground is at the bottom of the Bentley diagrams, and
the fuse box ( positive ) voltage is across the top.
Looking at it the conventional way like this, pin 25 is not a source of
voltage.
Right, on almost all cars, the ignition circuit is unfused.
There is no fuse anywhere between positive voltage and pin 15 on the coil.
Then we are in agreement and understand the circuit the same way.
'most' switching take place on the positive side of the circuit, but it
doesn't have to of course, could just as easily take place in the negative
side.
The horn circuit is an example of switching in the ground side.
Relays also - the ECU supplies ground to complete the pathway for the small
windings in the fuel pump relay, another example of switching in the ground
side of a circuit.
scott
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Dennis Haynes
Sent: Thursday, July 26, 2007 4:52 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Is ECU involved in getting power to fuel pump when turning
ignition switch on?
If you go with the fact that electrons are actually flowing from the
negative terminal of the battery to the positive, then you are correct that
pin #25 is a source. Since most folks see the positive as the source and the
negative as the "ground", ( which it really isn't) or common, we see the
positive and most switced connections as the source. This is called
conventional current flow.
Except for the wire from the ignition switch going through the fuse box, #15
on the coil is feed directly off the ignition switch. There is not even a
fuse in the way. Pin #25 completes the path to the chassis to control the
coil as you described. This is known as a "sinking" control circuit.
Dennis
>From: David Kao <dtkao0205@YAHOO.COM>
>Reply-To: David Kao <dtkao0205@YAHOO.COM>
>To: vanagon@GERRY.VANAGON.COM
>Subject: Re: Is ECU involved in getting power to fuel pump when turning
> ignition switch on?
>Date: Wed, 25 Jul 2007 21:11:37 -0700
>
>On the Bentley manual the #1 terminal is connected to the ECU's pin #25.
>This pin is a current source controlled by the ECU. Why is it a current
>source
>you might ask? It is because the ignition coil's primary winding is in fact
>an
>inductor. Current in an inductor and voltage across a capacitor are what
>you
>deal with for these devices.
>
>In order for the secondary winding to generate high voltage the primary
>winding
>is first fed with a steady DC current from the ECU pin #25 into the
>terminal #1
>and out from #15. Upon seeing a pulse from the Hall sending unit the ECU
>then
>cuts off the current momentarily. The ignition coil, an inductor, will
>react to
>induce an EMF to counter the sudden cutoff of the current. This induced EMF
>is
>transformed into a high voltage on the secondary winding.
>
>The current flowing out of the #15 of the primary coil is used to power
>both the
>power supply relay and the fuel pump relay. The voltage at the #15 is
>slightly
>less the ther battery voltage of 14 volts. It should be arround 12 volts
>still.
>1 - 2 volts are dropped off due to DC resistance of the primary winding.
>
>If for any reason the ECU loses the pulses from the Hall sending unit, it
>will
>cut off the current feeding the coil. as a result #15 terminal loses the 12
>volt
>which then shuts off the power supply relay and the fuel pump relay. Both
>the
>fuel pump and all injectors are no longer powered. You will have to turn
>the
>ignition off then turn it back on to start all over and energize both
>relays.
>If you begin to crank the engine and if the ECU sees the Hall signal it
>begins
>to feed the coil the required current again.
>
>If you have a defective rotor in the ignition distributor, a defective Hall
>sending
>unit, a broken high voltage wire for the center terminal of the
>distributor, a broken
>primary or secondary winding of the ignition coil, or of course a defective
>ECU
>the #15 terminal will not get the 12 volt. The power supply relay and the
>fuel pump
>relay are de-energized. The injotors will receive no power and the fuel
>pump will
>not pump. If your fuel pump is not getting power and is not pumping this
>should give
>you some hints for troubleshooting, in addition to checking the relays.
>
>David
>
>
>--- Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM> wrote:
>
> > Hi
> > Coil terminal 15 of course is the 'ignition on' 12volts DC , terminal
>of
> > course.
> > On a coil system terminal # 1 is connected to the points. ( in all
>this
> > wiring '1' is always associated with ground - points supply ground )
> >
> > Whether " Terminal #1 of the coil does get battery voltage " ....
> > Depends on how you look at it.
> > I'm sure there is voltage there during the process, but I wouldn't say
>it
> > 'gets battery voltage." I wouldn't say that at all.
> >
> > The purpose of ballast resistors as I understand them.....
> > ( a small embellishment to somewhat reduce one inherit weakness of
>points
> > )
> > is to reduce the voltage flowing in the points to help them last longer,
>arc
> > less, etc.
> >
> > during cranking to start, the resistor is bypassed so the points get the
> > full 12 volts , to perk things up to help the engine fire up , during
>'run'
> > the points get power through the resistor, which reduces the voltage.
> >
> > I should hope that an ECU that is directly involved with the primary
> > ignition circuit, as on 2.1 waterboxers and Subaru engines.....would
>change
> > dwell with rpm, as needed.
> > This is an example of how extremely compromised and lame points are
>compared
> > to electronic ignition.
> > It's even, I realize, very parallel to carbs/versus electronic fuel
> > injection.
> > The electronic system can be so precise, and optimized beautifully for
>each
> > different parameter, where the mechanical system, ( carb or points ) is
>a
> > general compromise, and subject to mechanical wear, as well.
> > Scott
> > wwww.turbovans.com
> >
> > -----Original Message-----
> > From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
>Of
> > Dennis Haynes
> > Sent: Wednesday, July 25, 2007 8:54 AM
> > To: vanagon@GERRY.VANAGON.COM
> > Subject: Re: Is ECU involved in getting power to fuel pump when turning
> > ignition switch on?
> >
> > Terminal #1 of the coil does get battery voltage. The ECU switches the
>path
> > to the chassis in response the hall sensor. Basic ignition coil
>operation
> > even back to points. Points closed or ECU conducting, coil is charging,
> > magnetic field builds. Points open or ECU opens, magnetic filed
>collapses
> > and high winding side of coil generates the high voltage to create a
>spark.
> > Back in the points day the condenser was needed to allow for the reverse
> > current as the field collapsed and prevent the points from arching.
>Dwell
> > was the angle how long the points were closed. Longer is better
>especially
> > at higher speeds. Minimum point gap was needed though to stop arc. Some
>cars
> > used ballast resisters to limit current at low speed, bypassed during
> > starting to compensate for lower battery voltage. ECU based systems will
> > change dwell in response to speed.
> >
> > Dennis
> >
> >
> > >From: Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM>
> > >Reply-To: Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM>
> > >To: vanagon@GERRY.VANAGON.COM
> > >Subject: Re: Is ECU involved in getting power to fuel pump when turning
> > > ignition switch on?
> > >Date: Mon, 23 Jul 2007 21:57:31 -0700
> > >
> > >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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> >
>
>
>
>
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