[Gmecm] Saturated/P&H injection

[davesnothereman at netscape.net]

Interesting question.  The 727 can definitely operate high impedance 
injectors without trouble.  That's what it's used with in OEM 
applications.  If you look at the 7730 <-> 7727 equivalency chart on 
Ludis' page you'll see the connection for "Injector A Sense" on pin D5. 
  This sense line is used with low impedance injectors in P & H mode.  
The P & H circuit may be calibrated to operate only (2) 2.0 Ohm 
injectors.  You might want to check into this a little further.

Zaphod

-----Original Message-----
From: Robin Handley <Robin at FuryWorld.fsnet.co.uk>
To: gmecm at diy-efi.org
Sent: Sun, 14 May 2006 20:48:59 +0100
Subject: Re: [Gmecm] Saturated/P&H injection

   Many thanks again. I knew about the difference impedances but the 
local
solution that I'd heard of involved adding a resistor. The GMECM 
triumphs
yet again!

Sorry for all the questions, but here's another one! Can the 727 do 
both?
(I've never come across any mention of a jumper in the time I've been
researching the 727.) I have a bunch of Bosch high impedance injectors 
which
I'd like to use.

Thanks,

Robin

----- Original Message -----
From: <davesnothereman at netscape.net>
To: <gmecm at diy-efi.org>
Sent: 14 May 2006 20:07
Subject: Re: [Gmecm] Saturated/P&H injection


> OIther than the fact that one indicates a single driver while the 
other
> is plural?
>
> Peak and hold injector drivers operate low impedance injector drivers.
> They allow higher current to initially open the injector, then when
> current reaches a peak level the driver switches to "hold" mode,
> limiting current to typically 1/4 of the peak value.
>
> Saturated injector drivers are designed for high impedance injectors.
> Total current draw through these injectors is lower than the low
> impedance types, so the driver simply allows maximum current through
> the injector coil at all times.  This scheme allows the injector coil
> to become "saturated" with current.
>
> P&H drivers will operate saturated type high impedance drivers.
> Saturated drivers are not intended to be used with P & H type
> injectors, although some people (and even OEM's) will do so with the
> aid of current limiting resistors.
>
> The 7749 can operate in either saturated or P & H mode selectable by 
an
> external jumper.
>
> Zaphod

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