Date: Wed, 25 Jul 2007 11:54:25 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Is ECU involved in getting power to fuel pump when turning
ignition switch on?
Content-Type: text/plain; format=flowed
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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