DIY_EFI Digest V5 #333

[John Dammeyer]

Hi James.

That may well be.  But that's only at larger throttle and heavily loaded
conditions.  The Honda 1600cc VTEC engines I worked on had, at idle,  a PW
of about 2.0ms with a 24lb pintle injector and about 1.75 with a 28 lb Lucas
Disc Injector (which open much faster).  This was with the O2 sensor
bouncing around 0.5V.

At 800 RPM this is such an incredibly short time compared to a single engine
revolution (75ms) that my software actually waited till the intake valve
started opening and the air started moving before I squirted so I squirted
2ms every 150ms (2 Revs).

At full power I needed about 12ms of injector on time which is longer than
one engine rev of 9.2ms so two pulses of just over 6ms each,  timed to the
TDC of the cylinder would have worked well and been easier to handle.  I did
a true sequential and had problems with timer resources but without knowing
precisely the injector on time the transition from firing once per every
second rev to once every rev is tough to handle and keep the engine running
smoothly.

What was interesting is that at one point the wiring harness had an error
and cylinders 2,3 were swapped.  The engine wouldn't idle below about 800
but we achieved full horsepower and torque.  When we found the problem and
swapped the cylinders back we found we could drag our idle smoothly down to
600RPM without a hiccup (Aircraft flywheel and no propellor so very very
light) and I believe the timing of the injectors were critical to that
smooth low pollution idle.  With the harness swapped back we did not see a
change at the high end because at that point the 28lb injectors were on for
72% of the time.

The injectors were started some time before the intake opened and closing
just before the intake valve closed. i.e. about 540 degrees before the
intake closed.

I think if you don't have a CAM sensor a fire every second revolution while
PW is less than X and then every revolution when PW is larger making sure
you add in the Open/Close time you could make an engine run well; especially
at higher revs.

John Dammeyer

> ------------------------------
>
> Date: Thu, 28 Sep 2000 09:22:14 -0700
> From: jamesc at venturalink.net
> Subject: Re: Some general questions about injection
>
> Don't most sequential systems, even with a cam sensor, still fire the
injector
> twice instead of once every 720 deg?  So you do get that one shot at the
closed
> valve, but also an equivalent shot during an 'open valve'.
>
> I believe the 4.6L Ford does, and certainly the turbocharged Buicks 5.0
Fords,
> even though they had distributor pickups.
>
> Mark
>
> John Dammeyer wrote:
>
> > Hi Nicholas,
> >
> > Since I went through this myself I'll try and answer some of your
questions.
> >
> > No,  it doesn't matter if it squirts into a closed valve.  In fact if
you
> > analyze a stock engine that meets emissions you'll see that they all do
> > this.  This is a good opportunity to dust off your high school math and
> > physics and do some calculations for yourself.
[giant Snip]

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