[Diy_efi] This turbo assist stuff, suggestions

[Mike]

At 03:26 PM 1/2/03 +0800, you wrote:
>Also didn't want to risk installing a capacitor that may have caused
>the ignition system to fail... adding capacitance may not be
>"welcome" by the ignition amplifier and finding a replacement part
>at this time of year is even less likely than me getting a day away
>from work about now.

I suppose that would be a concern if the +ve of the coil went into
the 'bosch amp' etc. On my setup the cap goes from ignition +ve to
ground somewhere near the ignition transistor. The ECU (by Bosch)
just drives a 500v NPN transistor which drives the coil directly,
but it is fully reliant on a 0.5uF cap near the coil +ve which is
the same as the +ve ignition line. After changing to 8uF the difference
is dramatic to say the least!

Your battery is effectively acting as a capacitor, though if you'd
ever seen the noise on a battery terminals from injectors and ignition
it would seem to be a very bad capacitor, batteries have a high
internal reactance though their internal DC resistance may be low.
In this respect the DC circuit is very different to the AC circuit,
the assumption is I take it, that there is some suppression within
the 'bosch amp', if its more than 10 years old and ove that time
has been subject to our Aust. conditions then its probably reduced
in capacity or suffers from resistance leakage - either way its
lacking in suppression.

It could be that were the car new and not modified then no extra cap
may be needed to suppress ignition noise from posibly upsetting the
timing start of ignition by the ECU. After a period of time, all
sorts of things become marginal and who knows what tolerance was
built into the initial setup - do you know what vintage is the
ECU electronics and what year the 'bosch amp' was manufactured ?

I and other engineers can probably be safe to say they can guarantee
that placing a good suppression cap from ignition +ve near your coil
(if this is the positive ignition supply) to ground (also near your
coil) wont do any damage but will improve dramatically the AC circuit
your ECU and ignition amp is seeing !

I take it you havent tried some other bosch amp as a swap ?

>There is no capacitor fitted to the vehicle, shown in any schematic
>or appearing anywhere in the parts catalogue for that type of engine
>management system.

There would have to be something - probably in the 'bosch amp', on
most schematics I've seen, its a separate cap due to issues like
size and reliability, I recall for one car it recommended replacement
each 100,000K ! Also over the last 25 years or so, I have
seen many errors in automakers schematics, omissions being the most
common.

How old is the car ?

And what is the specfic indication you get that the ECU goes into
retard mode, is there a light, beeper or just a dramatic drop in
power - or that zippiness sensation ?


Rgds

Mike
Perth, Western Australia
Some power/auto stuff here:-  http://www.iinet.net.au/~erazmus


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