Pulsed injectors on/off times

[Peter Berrevoets]

No, you've just created a whole lot more!

I'll start with this part because I can't follow it in the context you've
described below (sorry I'm no engineer)

"100% is OK! 85-99% is begging for trouble"

Earlier in the paragraph you mention that some don't fire at 100% so how
does this fit?

Peter Berrevoets
1990 200TQ
Toronto, Canada
http://frontpage.home.net/pjberr/



> >-----Original Message-----
> >From: quattro-admin at audifans.com
> >[mailto:quattro-admin at audifans.com]On
> >Behalf Of Jorgen Karlsson
> >Sent: Sunday, February 11, 2001 11:20 PM
> >To: Ameer Antar; quattro at audifans.com
> >Subject: RE: Pulsed injectors on/off times
> >
> >There is a simple way to measure the time it takes for the
> >injector to open.
> >A signal generator an oscilloscope, a .1ohm power resistor
> >and a drive
> >circuit is needed to do this. Using a car running at idle works.
> >
> >Connect the resistor in series with the injector, measure
> >the voltage over
> >the resistor with the oscilloscope, when you have got it to trigger
> >correctly you will have the shape of the current on the
> >display. It will
> >increase rapidly at the beginning and then start to
> >stabilize. Then at a
> >well defined point the current will start to increase
> >quicker again, this is
> >the point where the pintle bottoms out, the injector is fully open.
> >
> >If my memory serves me right the time before the injector is
> >fully open it
> >can be considered as half open.
> >
> >General times for a Bosch injector are 1-1.5mS, A Lucas disc
> >type injector
> >opens in 0.5mS. These are the only brands that I can
> >recommend. Bosch has
> >the better fuel atomization of the two, this to some degree
> >compensates for
> >the slow opening time.
> >
> >The max opening time can also be found in a similar way, but
> >it is a lot
> >harder to find the point. Different fuel pressures change
> >the max open time.
> >
> >IMPORTANT:
> >When the injector is used above it's maximum time it will
> >start floating.
> >This mean that the injector will deliver half as much fuel
> >as it is supposed
> >to!
> >
> >Stay with the 80-85% design rule, most injectors tend to
> >float at around
> >90-95%. some Rochester injectors float at 80% when the fuel
> >pressure is
> >high, raise the fuel pressure a bit more and they will not
> >open at all!!!
> >
> >The general rule is to design with half a pound per hp per
> >hour. That mean
> >that a 40lbs injector will support 80hp when fully open. By
> >following the
> >above rule it also supplies fuel for 40hp when it is 95%
> >open!!! Remember
> >this. 100% is OK! 85-99% is begging for trouble!
> >
> >
> >Then we have different types of fire sequences, many cars
> >use batch fire.
> >They Fire all injectors at the same time.
> >
> >Bank to bank fire is an other scheme, the injectors are used in two
> >alternating groups.
> >
> >Then we have the best way of doing it, Full sequential fire.
> >Each injector
> >is fired just in time for its intake valve to open. This
> >ensures that the
> >mixture will be perfect for all cylinders. Since the
> >injector only fires
> >once every other engine rev it will also have more time to
> >inject and to
> >close. This mean that the 80% duty cycle will be equal of a
> >conventional
> >scheme running at 90% duty cycle. The same goes for small
> >opening times, the
> >injector only fires at the open valve. The resulotion is far
> >better when
> >using full sequential.
> >
> >Audi uses sequential fire on the 20v engines.
> >
> >Good sequential EFI systems can also vary the balance
> >between the injectors,
> >really good injection systems can change the balance between
> >the injectors
> >depending on rpm and load! Good systems can also vary the
> >phase when the
> >injector fires and you guessed it, really good systems can
> >vary the phase
> >with rpm and load.
> >
> >Systems of the last type compared to a batch fire system has
> >far better idle
> >with 80LBS injectors then the batch fire system has with
> >40lbs injectors. If
> >we compare with CIS we could probably fit 160lbs injectors
> >and still have
> >far better idle quality.
> >
> >I hope that this answers a lot of questions.
> >
> >Jorgen Karlsson
> >Gothenburg, Sweden.
> >