EST Distributor

[Bob Wooten]

I see.  I think that you are right, it is time that I get another source of
information.  what I was using was the print in the manual & an educated
guess @ how it works.  the description that Keith quoted makes perfect sense
to me now.

the reference to the 8 engine code is to the VIN.  there were two TPI engine
codes in 91, one was 8 & the other F.  I think that the difference was one
was MAF & one MAP.  the distributor diagrams in the manual that I have are
different for them as well.  It appears that the 8 Engine code is the "HEI"
style of distributor with the Coil in cap & the F is the tall thin
distributor that I have that has an external coil.  but as I said, I don't
have that one so I don't know what it really is.

a fried of mine has an Iroc that is a MAF car.  His computer died & the GM
dealer told him that there are two ECM's for his car.  one has the coil
driver in the ECM & the other has another "module" that goes between the ECM
& the distributor.  this has always perplexed me as I don't recall having
ever seen a GM "Module" that was not either in the distributor or in the
ECM.  any thoughts or is this just another "parts guy" that doesn't know his
ECM from a hole in the ground?

Tanx, again to all.
BW

-----Original Message-----
From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf
Of Shannen Durphey
Sent: Thursday, March 29, 2001 6:06 PM
To: gmecm at diy-efi.org
Subject: Re: EST Distributor


Isn't this abbreviation in the FAQ?  It should be.

EST stands for Electronic Spark Timing.  This is a control mode.  The ECM is
in
control of spark timing (and dwell in distributor applications), with input
from
and output to the distributor.  The ecm also uses inputs from the other
engine
sensors to determine spark timing.  This is one of two basic spark modes,
the other
being Bypass mode.

I don't know what you mean by "the 8 eng coded 91".  The only distributor
which I
can think of with something close to EST, in addition to mechanical and
vacuum
advance units, is the 81 vintage 305 used in Chevy/GMC pickups.  This was an
ESC
system, which would retard spark when knock was detected.  I do not know of
any CCC
or later generation ecm/pcm controlled engine management systems which used
mechanical and vacuum advance in addition to ecm controlled timing.

You would be a wise man indeed to trade your Chilton's reference manual for
a real,
true GM service manual.  You should also consider finding the address for
the
company that supplies GM with its training materials, MSX.  The manual
titled "fuel
injection" will supply some very good reading material. Much of what you are
saying
is backward or misinterpreted, which could easily be attributed to a good
mind
learning from a poor source of information.

Shannen

Bob Wooten wrote:
>
> Questions #2, I think also another simple question.
>
> what is meant by EST?  I have a 91 Camaro that has an EST distributor (so
> says Mr. Chilton).  what I have noticed, & I am guessing but want to clear
> it up is that EST is more a scheme than anything.  this means that the
> Distributor controls the spark duties w/the small input from the ECM for
> retard & LHM.  this means that the distributor conditions the PU coil, has
> the driver in it for the HV coil & outputs a signal that is used to
> determine RPM.
>
> another guess is that all the EST setups do not have any Vac or Mech
advance
> to them, but?????  I noticed that the 8 eng coded 91 has the "standard"
HEI
> setup & I think (I don't have it so....) that it does have both Mech & Vac
> advance on it still.
>
> thanks for clearing that up.  here comes #3.
>
> Bob Wooten
> r71chevy at earthlink.net
> www.r71camaro.homestead.com
>
> --------------------------------------------------------------------------
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