Date: Mon, 17 Sep 2007 17:44:29 -0700
Reply-To: Michael Elliott <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Michael Elliott <camping.elliott@GMAIL.COM>
Subject: Re: Rich on side, lean the other?
In-Reply-To: <1b0df96d0709171730x6c4a85d6y4fd4138269d4792a@mail.gmail.com>
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Makes sense electrically. Yup, that it does. And I reckon the designers
thought that with individual feeds to the injectors they might, maybe, at
a later date, if properly inspired, have an ECU with separate output drives.
What I've asked the group twice and not gotten an answer on: three out
four times an injector fires at a closed intake valve? And the fuel pools
up or something until the valve opens and sucks it in?
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR
On 9/17/2007 5:30 PM tinker man wrote:
> Simple answer? Because it's connected that way at the ECU - take a
> look INSIDE the ECU where the connector is soldered to the PCB and
> you'll see that all four injector outputs are indeed wired in parallel
> (Euro Digijet 025 906 021F, no reason others versions are different).
>
> Technical answer?
> 1. For better performance: because of the high instantaneous currents
> involved driving the injectors and the limited wiring gauge available,
> each injector is connected right at the driving source, the ECU, to
> eliminate voltage drops (=> lower drive = reduced and inconsistent
> performance). Just like all POWER circuits in our home connect right
> to the fuse box, not one after the other in parallel on the same line
> coming from the fuse box, because each load further down the line
> would see a lower voltage due to voltage drops (magnified by the
> higher current of several loads in parallel) . Lower power circuits
> (e.g. lights) are indeed often cascaded in parallel. If we had
> unlimited gauge wire then this would not be a problem, but unlimited
> gauge creates physical implementation problems.
>
> 2. Keeping the above in mind, It's easier for wiring harness
> manufacture for each wire to go to a separate pin at the ECU
> connector. Otherwise, there would have to be a junction somewhere and
> again voltage drops would accumulate due to the limited wiring gauge
> from the ECU to this junction and reduced performance.
>
> 3. Redundancy/reliability - in case there's a problem in one of the
> circuits/injectors (e.g. lower resistance/partial short between
> windings), preventing the culprit from robbing all the drive power
> from other injectors (again lowering performance).
>
> Anyway we look at it, even if they fire in parallel, this topology is superior.
>
> TM
>
> On 9/16/07, Michael Elliott <camping.elliott@gmail.com> wrote:
>> On 9/16/2007 8:31 AM Raymond Paquette wrote:
>>
>>
>>> I don't doubt that you know what you're talking about, but that seems
>>> bizarre. Why then is there an injector at each cylinder, instead of one big
>>> one in the throttle body? Faster response? Why not more than one per
>>> cylinder, or one on each bank?
>> Bentley's 97.55 shows each injector getting its own individual feed from
>> the ECU.
>>
>>
>> --
>> Mike "Rocket J Squirrel" Elliott
>> 71 Type 2: the Wonderbus
>> 84 Westfalia: Mellow Yellow ("The Electrical Banana")
>> 74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
>> KG6RCR
>>
>
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