[Diy_efi] Electronic expertise requested

[bcroe at juno.com]

Dan, 

For you, the answer is probably 2 sets of injectors.  The 
backup set perhaps would not need to be quite as optimum.  
How about a different EFI for each cylinder, if you could run 
with one dead.  

Here I am contemplating a Q-jet system, then add port injectors.  
With EFI the fuel inlet to the carb is off.  If the EFI dies, I just 
turn on the gas to the carb.  

An injector driver has a transistor that usually fails short 
(injector full on).  Adding another parallel transistor won't 
make the short go away.  When the injector is turned off, 
the energy kicks back to the driver.  Getting all these things 
to transfer over after a failure will be tough.  

The reliability business will never be simple, we take it 
pretty seriously in the phone business.  It reduces to this.
Analyze every possible "what if" that could possibly go 
wrong.  That is not a short list.  Then figure a way to back 
up anything.  Trouble is, the new parts added have to be 
analyzed all over, generating a new list of problems.  It 
never ends, just try to converge quickly on an acceptable 
level of failure.  

Bruce Roe

18 Jun 03 "Daniel R. Nicoson" <A6intruder at adelphia.net> writes:
> Thanks for the response Bruce.  A relay system could 
> start to up the parts count and failure points as well.  Is 
> there any source on the net that discusses failure 
> probability of these various components in language a 
> mere mortal can understand?  You guys that design for 
> a living must have to calculate a failure probability on 
> your projects at your day jobs?
> 
> I also owe you an apology.  I had promised to run tests 
> comparing the DIY-WB to my 4-gas analyzer.  I haven't 
> made it to that project yet.  Hopefully I can yet this summer.
> 
> Thanks,
> 
> Dan
> 
> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org 
> [mailto:diy_efi-bounces at diy-efi.org]On
> Behalf Of bcroe at juno.com
> Sent: Wednesday, June 18, 2003 7:36 PM
> To: diy_efi at diy-efi.org
> Subject: [Diy_efi] Electronic expertise requested
> 
> 
> In general, you can't just connect 2 computers to your
> injectors, the one that is "off" will still conduct current
> in some situations.  Anyway, a failed injector driver
> could defeat attempts of the backup to take control.
> 
> Systems CAN be designed to operate as you desire.
> Short of a custom dual unit, I suggest you use a relay
> to switch over the injector wires to the backup when
> it is powered up.  Another way is just have a second
> set of injectors.
> 
> Bruce Roe
> 
> 18 Jun 03 "Daniel R. Nicoson" <A6intruder at adelphia.net> writes:
> 
> > Can one set of injectors be hooked to the two engine computers
> > (Ford EEC-IV's in this case) at the same time if only one EEC is
> > powered at any time?  The point would be that if one computer
> > fails, flip the switch and the second computer powers up and
> > runs the injectors.  My intention would be to have a backup EEC
> > much like many race cars use a backup ignition system.
> 
> > Dan Nicoson
> 
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