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Date:         Thu, 26 Jul 2007 12:51:58 -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?
In-Reply-To:  <000001c7cfb1$addab0e0$6401a8c0@TOSHIBALAP>
Content-Type: text/plain; charset=iso-8859-1

Electricity flowing from positive voltage point to negative point is just a concept for convenience. It is closer to the reality that it is electrons that moves in the opposite direction. For AC current the electrons are moving back and forth. They never really flow to anywhere.

The best way to describe how the ignition coil works is to look at it in a current point of view. It would be necessary to look at a voltage point of view if the device is a capacitor.

Basically the primary winding of the coil needs to have an initial DC current flowing to produce maximum magnetic field at the iron core. To induce a high voltage across the secondary winding you cut off the current as fast as you can. The high voltage produced across the secondary winding is an induced EMF by the rapid collapse of the magnetic field in the iron core.

Dennis explained this correctly in an easier to understand fashion. ECU pin #25 should be grounded initially and is switched to open (to cut off current) upon seeing the Hall signal than quickly back to grounded state waiting for the next Hall signal. It is really an electronic point that doesn't arc and doesn't wear.

David

--- Scott Daniel - Shazam <scottdaniel@TURBOVANS.COM> wrote:

> 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----- > === message truncated ===

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