[Diy_efi] Re: CIS EFI via Fuel Pump PWM

[Bernd Felsche]

Kenny W tapped away at the keyboard with:
> Quoting Kenny Bauman <kennybauman at yahoo.com>:

> > Not sure I understand the 100:1 range needed of
> > the
> > pump.
> > 
> > Perhaps you can clarify?

> I think that's a little extreme, as actual efi systems 
> rarely if ever vary duty cycle from 1 all the way to 
> 100%, which would be varying fuel delivery in a 100:1 
> fashion. I think the main issue with making this work 

100:1 is order of magnitude... 30:1 to 50:1 is expected in most
applications. A 200+kW turbo'd Audi doesn't consume a heck of a lot
of power to idle. Little more than the unturbo'd base engine -
perhaps even less.

> has been covered, that the pump response would be an 
> issue wrt to it's intertia and overall damped step 
> response. It makes more sense to run the pump 
> constantly and switch somthing that has a better time 
> constant both electrically and mechanicaly. Another 
> issue is that fuel in the lines after you shut the pump 
> off will dribble out of the injectors, you need some 
> sort of positive shutoff. You'd need a solenoid valve 
> located as close to the injectors themselves as 
> possible. And now you're back to having a return line 
> so you haven't really solved anything- you might as 
> well be running efi. 

Also worth considering is that Bosch's CIS used a pressure
accumulator to damp the pressure p[ulses from the fuel pump; largely
so as not to upset vehicle occupants, but I gather also to reduce
the likelihood of the pressure pulses bringing about nasty harmonics
in the fuel distributor.

> One thing that would be interesting though is to 
> replace the CIS flapper door with a hot wire AMM. A 
> unit that reads the AMM voltage and with one lookup 
> table outputs a voltage to a proportional valve that 
> varies the pressure just like the mechanical valve 
> operated by the flapper door. This would allow you to 
> use a huge AMM and eliminate the airflow limits many 
> conventional cis distributors impose. But again, buy 
> this time you could have converted to EFI so most of 
> this is pretty moot imo. Now where did I put that 
> medication?...

Such a system was discussed about a year abo, IIRC.

-- 
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