Re: 4wd range selector / vss in 747 application

["Bruce Plecan" <nacelp@bright.net>]

> 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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