[Diy_efi] Ignition/coil

mark krawczuk krawczuk
Fri Mar 24 12:25:56 UTC 2006

hi, i thought that the wire  used for ballast resistor is a    special
nichrome / resistance wire ?

mark k

----- Original Message -----
From: "Bill Washington" <bill.washington at nec.com.au>
To: <diy_efi at diy-efi.org>
Sent: Friday, March 24, 2006 5:45 PM
Subject: [Diy_efi] Ignition/coil

> David,
> Most coils are 9V fed thru a ballast resistor during normal running to
drop the
> 12V(nominal 14V really) to about 9V. During cranking the ballast resistor
> shorted out to provide extra 'oomph' because the battery voltage sags
> cranking.
> If you go looking for this 'Ballast' resistor in most cars you will not
find it
> because the actual wiring is sized (small) to provide the resistance, and
> cranking a lower resistance path is connected in parallel either by the
> switch or by a relay.
> In a ballast resistor system, if the supply side has been modified (ie the
> resistive wire bypassed) or the relay has failed with the contacts
> closed you will have lots of spark but a short coil life....
> If the car was designed for a 12V coil, ie it does not have a ballast
> and a 9V coil is fitted the result is the same - lots of spark, short coil
> Some years ago an "auto electrician" without my knowledge fitted a Bosch
> (9V) coil in place of my GT40 (12V) coil when a workshop had trouble
starting my
> car (I had told them that they would not be able to start it and to call
me, but
> they "knew" better) - My car had a 12V coil standard - and no ballast
resistor -
> the coil only lasted a few weeks!!! and I had to replace it - the workshop
> refused to accept any responsibility - needless to say they have never
seen any
> of my cars again!!!!
> Just some thoughts
> Best Regards
> Bill
> Subject:
> Re: [Diy_efi] Bosch ignition coil
> From:
> "David Allen" <davida1 at hiwaay.net>
> Date:
> Thu, 23 Mar 2006 21:12:22 -0800
> To:
> <diy_efi at diy-efi.org>
>    Thanks for the info on DIN 72552.
>    As for the iginition system in general; it's a remote-coil HEI.  The
> resistance of the coil-to-cap lead is 12K, and the plug leads range from
> to 13K depending on length. The cap and rotor had evidence of cap/ rotor
> interference but the contacts were clean and the rotor tip wasn't broken
> off.  I replaced both as a set.  The plugs are Bosch Platinum (original;
> multi-tip etc..) gapped at .045". Engine is a 305 running about 10:1
> compression normally aspirated.  There haven't been performance issues
> betwen coil failures.
>    With each coil I replaced the cap and rotor shortly after and tested
> wires, suspecting the high secondary resistance issue you describe. I've
> never had a module outright fail on this car. The new one on there now was
> purchased as a replacement for one I had to "borrow" to get my other car
> running.
>    I think the coil quality may be the problem.  The last couple times the
> coil has died I have been on the road and had to locate a local parts
> to buy a coil. The choices have been limited.  Will see how this one holds
> up.
>    Thanks for the ideas. I do have a great apetite for adventure and no
> to worry about so I will let the module stay for now!  :-)
>    I plan to measure the peak primary voltage and see how this is affected
> changing to non-platinum plugs.  I remember a thread where someone was
> concerned they were damaging plug wires by use of platinum spark plugs. It
> sounded far-fetched but you never know.
> Later,
> David
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