ECM Tolerances? EEPROM PCM in LT1

[Kurek, Larry]

Well, the 94+ EEPROM PCM's in the F-bodies have what is known as a
replaceable "knock module" which plugs into the PCM through an access
cover, similiar to the way old chips did. The KM is where the knock
filtering and conditioning occurs. What I tried was to switch modules
between the PCM's as well, and no major difference in results. 

However, this issue goes WAY past just the knock retard issue in the
PCM. I can understand how controlled devices can give different results
by different programs in the PCM itself. However, why are the sensors
giving me different feedback as well? It isn't just a matter of degree,
like a voltage difference would provide, but an actual difference in the
characteristics of the curves resulting from the sensor output. For
instance, ho is it that my MAF sensor with the old computer would peak
out at around 230 gps at the rev limiter, while with the new PCM I'm
getting around 260? Same engine. Same sensor. Same weather conditions...
Unless there are production differences in the PCM where a certain
frequency input from the MAF is interpreted as one airflow rate vs
another...but I would think that is a software function anyhow.
Again...still searching.

Later,

Larry

> -----Original Message-----
> From:	Roger Heflin [SMTP:rah at horizon.hit.net]
> Sent:	Thursday, August 20, 1998 2:20 PM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	Re: ECM Tolerances?  EEPROM PCM in LT1
> 
> Bruce, 
> 
> I  am going to post to this list what I posted to the fourth-gen list
> for
> larrys article. 
> 
> 
> The knock sensor filter is in the computer. (I think).   Maybe one of
> the
> filters is broken and the other is working correctly?  There is
> generally
> quite a bit of deviation in analog filter design, it is real hard to
> get
> them exaclty the same, even with components with pretty good
> tolerances.
> So both filters might be mostly working just working differently, and
> one
> is filtering more of the "junk" (false knock) out.
>  
> In the <94 I believe the knock filter is in the Calpack.  At least
> that is
> what something I read claims is the thing in the rest of the calpack.
> So
> it would be possible on a 93 to get different results by changing the
> chip
> (and therefore the knock sensor filter) with exactly the same
> programming
> in the chip.  I wonder if anyone adjusts these?
>  
>                         Roger
> 
> 
> On Thu, 20 Aug 1998, Bruce Plecan wrote:
> 
> > 
> > -----Original Message-----
> > From: Kurek, Larry <LKurek at ocfexch2.ocf.anl.gov>
> > To: 'diy_efi at efi332.eng.ohio-state.edu'
> <diy_efi at efi332.eng.ohio-state.edu>
> > Date: Thursday, August 20, 1998 2:29 PM
> > Subject: RE: ECM Tolerances? EEPROM PCM in LT1
> > 
> > 
> > > Peter wrote:
> > > >Hi Larry
> > > >Not sure. Please take this with a grain of salt
> > > >1.      An 8051 PCM can have different cals.
> > > I know this...but we both have 94 LT1's with identical engines,
> > >and manual transmissions. The only difference is the PCM I borrowed
> is
> > >from a Pontiac and mine is a Chevrolet. Same part numbers though...
> > 
> > <snip>
> > 
> >  The Left and right O2's
> > >were actually fairly similiar at WOT, yet the pulse widths were
> > >different by a few .1 milliseconds.
> > > >later:peter
> > > <SNIP>
> > > Thanks!
> > > Larry
> > 
> > 
> > This is most interesting,  I've talked with a few other folk
> relative to
> > some forms of racing where things must be pure stock, and they
> > try an arm load of ecm's to get the most HP.    This is not just a 
> > gm issue.   The folks I talked to didn't have the ability to measure
> 
> > the PW, so this was an unknown, but to actually hear that there 
> > is, is rather enlightening.
> >    Seems like another perfect bench ecm test.  
> > Cheers
> > Bruce
> > 
> >