Re: 4wd range selector / vss in 747 application

[Shannen Durphey <shannen@grolen.com>]

What's this, a verbal emissions test?
Model years, I just got back from a cruise night.  It's amazing how
many shiny new edelbrock and carter carbs are getting installed.  EFI
swaps are still kinda uncommon in this area.
Shannen

Bruce Plecan wrote:
> 
> > Hey, now.  Things aren't considered "old" around here till ya get back
> > into the forties. : )
> 
> model years, date of birth (ie 1940s), or just human age.
> Your answer will be scored
> Grumpy
> 
> > Shannen
> >
> > Programmer wrote:
> > >
> > > Yep--you're right. Affects 87 and 88 5.0 and 5.7L trucks...Thanks
> Shannon.
> > > Guess I
> > > haven't had a real "old" one in for a while...
> > >
> > > Lyndon.
> > > -----Original Message-----
> > > From: Shannen Durphey <shannen@grolen.com>
> > > To: gmecm@diy-efi.org <gmecm@diy-efi.org>
> > > Date: August 17, 2000 7:28 PM
> > > Subject: Re: 4wd range selector / vss in 747 application
> > >
> > > >See Chevrolet bulletin 88-180-6E.  Also, I know it can happen on
> > > >manual trans vehicle.  It was pretty easy to set the code on the
> > > >hoist, by running the engine at higher rpm while the rear wheels were
> > > >spinning, but the trans was not in gear.  The bulletin talks about new
> > > >calibrations to prevent it, prolly an issue with 88, 89 trucks.
> > > >Shannen
> > > >
> > > >Programmer wrote:
> > > >>
> > > >> Shannon,
> > > >> I don't recall ever seeing a VSS code unless the PRNDL switch input
> > > showed
> > > >> P/N. Otherwise, no codes "should " set, even in low range...
> > > >> Lyndon.
> > > >> -----Original Message-----
> > > >> From: Shannen Durphey <shannen@grolen.com>
> > > >> To: gmecm@diy-efi.org <gmecm@diy-efi.org>
> > > >> Date: August 16, 2000 5:03 AM
> > > >> Subject: Re: 4wd range selector / vss in 747 application
> > > >>
> > > >> >Niinikoski, Juha wrote:
> > > >> >>
> > > >> >> I don't have any 4wd truck wiring diagrams so can anybody help me
> on
> > > >> this. I
> > > >> >> don't know if a switch is needed to inform 747 ecm if the transfer
> > > case
> > > >> is
> > > >> >> in low range. If it is what is the input pin for this information
> ?
> > > Are
> > > >> >> there other tricks how ecm handles lo range ? In my conversion
> easiest
> > > >> place
> > > >> >> to build vss is inside speedo. This way it is always going to
> > > represent
> > > >> >> absolute vehicle speed.
> > > >> >There is no low range input to the 7747.
> > > >> >ftp://diy-efi.org/incoming/747auto_pinout.zip
> > > >> >That is where the VSS is usually placed.  4X4 pickups have a VSS in
> > > >> >the transfer case.  There are no tricks, except that the ECM can set
> a
> > > >> >VSS code if low range is used.  If the engine rpm stays above a
> > > >> >certain level, Vacuum is high, and vss signal is below a certain
> > > >> >speed, a code 24 will be set.
> > > >> >>
> > > >> >> What I have understood so far is that vss input is important for
> ecm
> > > to
> > > >> >> handle idle adjustments and prevent stall on decelerating
> conditions.
> > > >> What
> > > >> >> is not clear for me how ecm handles same situations in lo range.
> Going
> > > >> >> downhill you may have very low speed but same engine conditions
> than
> > > in
> > > >> road
> > > >> >> speeds.
> > > >> >Low range is handled by the same maps as high range.
> > > >> >Shannen
> > > >> >>
> > > >> >> Thanks Juha
> > > >>
> > >
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