Sequential Injection injector overlap?

[John Dammeyer]

>Date: Wed, 8 Sep 1999 19:36:34 EDT
>From: PHXSYS at aol.com
>Subject: Sequential Injection  injector overlap?
>
>Hi
>
>I was wondering if anyone knows if the injector pulse widths overlap on
>sequential injection. The application is a Chrysler 3.3 v-6, 97 model year,
>but I am sure GM is similar. What I mean by overlap is, say injector 1 has
>fired, is it possible (or likely) for the next injector to fire while the
>previous injector is still on?
>
>Thanks
>
>Jon


Yes.
.......
OK.  I'll elaborate.  ;-)

Basic rules for injector selection are as small as possible in order to be able
to accurately meter out the tiny quantities needed at idle.  Otherwise you may
find that the injector has been asked to open,  then close before the pintle
barely even moves off the seat.  You can assume that an injector needs at least
1ms as a minimum pulse width.  If the injector is too large idle will be rough
and erratic.

Down side of this is that the injector must then open before the intake valve
opens in order to supply enough fuel and at full RPM the injector may be open
for 80% of an engine cycle.  ie:  at 6500RPM (18ms) it could be open for 14ms so
it actually turns on during or at the end of the the power stroke of the
cylinder.

Because each cylinder in a 4 cyl engine has a power stroke the injectors do
indeed overlap and you might have 3 of them on at the same time at high revs.

There are all sorts of tricks you can use to get around this rough idle.  An
extra throttle body injector for idle speeds is one.  A dual set of injectors, 1
small and the other big much like the two barrel carburetor.

Honda,  in order to have a smooth idle and raw power at the top end uses a
14lb/hr injector for their 1600cc VTEC engines.  They have a smooth idle because
the CAM is mild mild mild until 4000RPM at which point the VTEC solenoid is
activated and the intake profile goes to HOT HOT HOT.  Even so,  the 125HP
engine can just barely make rated horsepower with 14lb/hr injectors and about an
88% duty cycle.  In other words I don't believe the engine in the street
configuration is rated for sustained full power at the top RPM without
overheating the injectors.   But it does run continuously at peak torque RPM of
5200RPM with about 50% injector duty cycle.

Regards,

John Dammeyer