GM Fuel Pump control scheme

[Jake Kooser]

Can somebody direct me to a thorough description of what "limp home" mode is
with a '747?  The van my TBI came off of was allegedly only firing one
injector.  Is that limp home mode?  The engine itself is working fine, just
keeping an eye out for problems I may run into when I do the TBI re-install
on the engine.  Thanks,

Jake Kooser

> -----Original Message-----
> From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf
> Of Ludis Langens
> Sent: Monday, January 29, 2001 2:07 PM
> To: gmecm at diy-efi.org
> Subject: Re: GM Fuel Pump control scheme
>
>
> WEG1192 at aol.com wrote:
> >
> > To me its obvious that Steve Ravet was right in that the OP
> switch is used to
> > keep the pump running during CPU failure, otherwise limp home
> wouldn't work
> > period. I can also say for certain that the ECM keeps the pump
> running as
> > long it recieves ignition pulses from the distributor. [...]
> > The only plausible resaon left is to keep the pump running during
> > limp home mode.
>
> One problem with your theory - the fuel pump relay is controlled 100% of
> the time by the limp home circuit.  The CPU (and PROM) need to do
> nothing to operate the fuel pump relay.  In fact, they can't
> control the relay.
>
> When initially powered up, the limp home circuit turns on the relay
> briefly, and again whenever there is a distributor reference pulse.
>
> --
> Ludis Langens                               ludis (at) cruzers (dot) com
> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/
>
>
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