420 SBC project..was Re: selection of TBI components for 383 Chevy

Shannen Durphey shannen at mcn.net
Wed Oct 15 03:53:09 GMT 1997


Curtis L. Martin wrote:

> <snip.>
>
> > FYI: ESC module retards ignition in 4deg. increments then advances 1 deg
> at at
> > time until it can retadr it again.
>
> Do tell..  I was under the impression that the GM knock sensor was an all
> or nothing deal, if the sensor trips, then the ECM dumps 30 degrees of
> timing to suppress knock.  (Or are you referring to what the HEI module in
> the distributor base is capable of ?)

Actually, I was a little off.  Knock sensor pulls down voltage from KS
module
to about 2.5v.  Module interrupts timing from ecm and retards signal in
2 to 4
deg inc. Then when voltage on KS signal line increases  to 5v, module
adds
timing  2 to 4 deg at a time.  Some ECMs have Knock control built in. 
Works
the same way.  Actually, KS adds(or subtracts) A/C voltage to 5VDC on
signal
line.

>
>
> > > > Ignition with be stock HEI.
> >
> > Accell Supercoil on large cap HEI welds advance mechanism solid.  Details
> at
> > 4500+ rpm :-(

> Could you run that by me again in english?  I don't understand what you
> mean by that.
>

OK.  Grey ACCELL coil mounted on top of the cap of an HEI dist. will
cause the
ignition module to produce extra pulses.  On an older mechanical
distributors,
like my Buick 455, this causes random sparks which eventually break down
the
center of the rotor, arc between the advance mechanism and the shaft and
weld
it together.  On newer computer controlled distributors extra module
pulses
cause extra reference pulses to be sent to the ECM.  This can mean as
little as
seeing incorrect rpm on the scan tool or as much as extra injector
pulses,
advanced timing, and rpm/fuel cutout too early. When I ran into this
problem on
my car, I thought that something was causing the advance to get too hot,
and
spin the grease out of the shaft.  I made it regular maintenance to
clean and
lube the advance.  I found an article in Car Craft which contained the
answer.
Their solution was to buy an Accell module, more resistant to the
effects of
the coil's mag. field, and to use the special kit which mounts the coil
remotely, uses high tension lead and adapter to carry spark to
distributor.  I
never tried it.You could use a small cap type HEI dist. from a '90 GM
pickup,
which uses a remote coil.

>

Shannen



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