4-cyl HEI in GM Autos?

[Shannen Durphey]

alk

Clare Snyder wrote:

> Garfield wrote:
> >
> > On Sat, 29 Nov 1997 12:32:33 -0500, Clare Snyder <clsnyde at ibm.net>
> > wrote:
> >
> > >It's official!
> > >
> > >The same module is used on 4,6,and 8 cyl vehicles. Echlin/Napa part#
> > >TP25 fits the following, and mabee more:
> > >92 spectrum 1.5L
> > >86 Cavalier 2.0L
> > >86-90 Caprice 4.3L
> > >86-88 MonteCarlo 4.3L
> > >1990 Caprice 5.7 pursuit
> > >1989 Caprice 5.7
> > >88-89 Camaro 5.7
> > >87-88 MOST 5.0L
> > >
> > >TP22 fits the following:
> > >83 Cavalier 2.0L
> > >90-92 Camaro 3.1L
> > >88-89 Camaro 2.8L
> > > etc
> > >
> > >
> > >I'm not going to say "I told you so", or rub your face in it or anything
> > >:} Just go for it!!!!
> >
> > Uh, huh. Yeah, far be it from YOU, Clare, to say "I toldya so". Hee.
> >
> >



> <snip>
> >
> > Just to sneak my previous reasoning back into the
> > discussion/argument/armwrestling, since the module is used on a 4 and an
> > 8, and kicks in some advance above high idle, the AMOUNT of advance
> > observed and WHEN (rpm) it kicks in is gonna be way diff., unless the
> > module is clairvoyant or can just "feel" the number of cyls. Heh. That's
> > why I conjectured/pontificated that they just *couldn't* be used on any
> > ole #ofCyls. But hey, who am I to argue with the Parts Book, eh? Some
> > times "science" just fails us. Sigh.
> >
> > Garfield
>
> You got my answer on that one already, Gar. IF it works the way I
> described it, it does not need to know how many cyls  there are, and
> from what I have heard, you can use the unit on a one lunger with the
> same results as on an eight. Use 4 on your 4 cyl for DIS.
> Again, I may be wrong, but I'm batting 100 so far :}
> -

  Electronics aside, in the interests of reduced manufacturing overhead and
part number consolidation one might be tempted to use the most "conservative"
module produced by OEM in all applications where it will fit.  Remember that
we're talking about advance during a loss of computer controlled timing here.
Whether or not the module delivers 4, 6, or 10 deg. advance, the driver is
still going to notice a check engine light and a large loss of power. I would
guess NAPA is more concerned that they have no problems when everything is
working correctly.

The explanation about the B&S ign. system makes sense to me, and it sounds like
this system has a gradual timing increase as rpm increases.  The module in my
pickup, a GM part, has no advance until around 2500 rpm, and then BOOM it's
advanced.  All or none.

Knowing that GM makes electronic advance possible in the ECM by sending a
reference pulse which is 7 cylinders delayed, (or 90 cs degrees advanced), and
then retarding it, I would guess they do something similar within the module
when needed.  Although honestly I have no idea how this is done.

And while I'm thinking of it, the rise in voltage from the pickup coil to a
certain level causes the module to close the primary circuit..  This energizes
the coil.  It's the drop in signal voltage and the resulting open circuit to
the coil which causes a collapsing mag field and spark.  What you have
described is the increase in -dwell- which is indeed a feature of the module.

Whew.

Shannen