GM Fuel Pump control scheme

[Bob Wooten]

Bob,

tell me that it is not common practice that you carry a spare ECM in the
car?  i was thinking about putting the OP switch in the car after this
thread, but maybe just a complete
ECM/harness/injectors........................ your right someone did get a
good laugh, thanks
BW


> [Original Message]
> From: Bob Valentine <bob at tecmark.com>
> To: <gmecm at diy-efi.org>
> Date: 1/28/01 11:07:21 PM
> Subject: RE: GM Fuel Pump control scheme
>
> Yikes, I started a monster with this.    My Cutlass doesn't run a OP
> switch, and I've never had a problem either.   I ran a few miles in limp
> home, no problem with FP tho...  This was with a '730, V8 memcal.   
> 
> Limp home mode was caused due to flashlight falling off seat onto ECM thus
> knocking exposed eprom in ZIFF socket out of socket, while spilling cup of
> coffee into ECM in attempt to grab said flashlight .     Hope someone gets
> a laugh out of this.  Wasn't very funny in East Nowheresville, PA at 1am,
> on the way to the efi pow-wow last year.  Spare ECM got me out of that
jam.   
> 
> -> Bob Valentine
> -> bob at tecmark.com
> 
> 
>    
> (on the way to the efi pow-wow no less.... 
> At 09:35 PM 1/28/2001 -0700, you wrote:
> >I have done a few conversions on my vehicles and have not used an 
> >oil pressure switch in any of them.  I think the OP switch is just a 
> >back-up for the fuel pump relay.  Good thing to have in case the 
> >relay goes out while driving on the hi-way at high speeds.  I have 
> >had one relay go out on me when off road in the middle of nowhere. 
> >I had to wire the pump into a spare switch in the dash to be able to 
> >turn it on and off when needed.
> >
> >On 28 Jan 2001, at 23:14, Keith D. Miller wrote:
> >
> >> > -----Original Message-----
> >> > From: owner-gmecm at diy-efi.org 
> >> > [mailto:owner-gmecm at diy-efi.org]On Behalf
> >> > Of Bob Wooten
> >> > Sent: Sunday, January 28, 2001 10:37 PM
> >> > To: gmecm at diy-efi.org
> >> > Subject: Re: GM Fuel Pump control scheme
> >> > 
> >> > 
> >> > I have beenthining about this for a couple of days  & i am
> >> > still confused. if this were in fact to kill the engine if
> >> > the oil pressure dropped below the switch threshold & that
> >> > the redundant CPU relay was just for starting, then this
> >> > would make a lot of sense (kind of).  I would think that
> >> > putting in a switch to tell the cpu OP OK or OP BAD would
> >> > do the same thing.  the thing that i don't get is that my
> >> > car does not have a OP switch & it has never had a problem
> >> > with it running.  this tells me that the cpu must be
> >> > turning on the FPS relay & keeping it on (& it is
> >> > obviously not hot wired on as the CPU turns in on when i
> >> > turn the key on & then turns it off until the motor is
> >> > running).  this tells me that the OP switch is a
> >> >  completely redundant system.  the question is why.  
> >> > 
> >> > It does not make sense to me that the general would put
> >> > this in because the relays have a tendency to fail.  if
> >> > that were the case then good engineering says that you
> >> > spec a higher amp relay or put two of them in series with
> >> > each other so that the cheaper less amperage relay can
> >> > drive the coil of the power relay (kind of like a
> >> > darlington pair or a industrial controller).  one of the
> >> > gents on the list suggested that this had to do with limp
> >> > home mode & that does make some good sense.  If i am
> >> > right the resistors & "stuff" on the memcal does
> >> > something to the cpu to control injectors, the ign module
> >> > does spark & the other thing has to be fuel.  I would
> >> > think that there is a more high tech approach, but
> >> > sometime simplicity is the best way to go.  
> >> > 
> >> > Am i thinkin' to hard?  
> >> > thanks for listening. 
> >> > BW
> >> > 
> >> 
> >> Maybe, maybe not. We all know the ECM charges the rail fuel
> >> pressure at startup. Does it also provide power to the fuel
> >> pump once the motor has started? Or is that done only by the
> >> oil pressure switch after the motor has started?
> >> 
> >> The answers to those questions would likely show the
> >> original intent of the design.
> >> 
> >> Keith
> >> --
> >> 88 CSC (Down, but not out)
> >> kdmiller at westnet.com
> >> 
> >> 
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> >> 
> >
> >
>
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--- Bob Wooten
--- r71chevy at earthlink.net
--- www.r71camaro.homestead.com



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