injection timing

[Stephen Dubovsky]

At 04:57 PM 8/26/97 -0400, you wrote:
>
>How come a Bosch CIS ( continuous injection ( mechanical)) on a Porsche
>924 ( or any audi /VW for  that matter of the late 70's ) tends to have a
>MUCH smoother idle than many newer sequential efi systems. ??  The spray
>is always sprayed constantly, at the intake valve, and to mee that would
>cause puddling, and rough idle, but ironically runs smoother and better
>than most efi systems.  My car with a stock ( but soon to be modified CIS
>(K-Jetronic)) is capable of idling STEADILY at under 300 RPM. A stab at
>the gas peadle gives immmediate response. ( nearly impossible to stall it
>even at the low idle when just jabbing at the accelerator.)
>
>Anyone ever consider adding a feedback system to CIS other than
>KE-jetronic's (frequency valve ) ???  (trick is to modulate "control
>pressure", (formerly from the warm up regulator,  why not put in a
>variable valve to control pressure in the circuit to give  closed loop
>fuel delivery ?
>
>
>Just some thoughts for chewing..
>
>Dave
>
>

Actually the CIS (K-jetronic) is closed loop.  The system pressure is set
up to run rich (good for WOT) and leans the system out to stoic by letting
some air 'leak' around the metering flap (or is this the 'freq valve' you
refer to in the KE-jetronic?)  Anyway, the only real difference in leaning
the mixture and lowering the fuel pressure is that you could probably
reduce the idle speed a little bit more in the fuel-P system.  My 83 3.0L
911 (last year w/ CIS) used to idle at 800-1000 rpm, but now w/ a K&N air
filt idles at 1500.  Something about improved flow;)  BTW, it still idles
at 800-1000 at startup, but runs rich until the O2 sensor heats and puts
the system in closed loop;)  I SHOULD go in and set the idle speed better
by adjusting the flap or throttle body, but what's wrong w/ running a
little rich at startup;) (BTW, I also have the air-intake pop off valve to
keep the rare backfire on VERY cold mornings from blowing up my airbox).

Just a few, but sometimes worthless, thoughts...
Stephen Dubovsky