Injector control

[Greg Hermann]

>-----Original Message-----
>From: Greg Hermann <bearbvd at sni.net>
>To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
>Date: Thursday, November 26, 1998 10:02 AM
>Subject: Re: Injector control
>
>
>>>Hi Greg,
>>>A couple of thoughts regarding PW.
>>>1). The smaller you make the PW (resolution) the more Processing Power
>>>(MIPS) you need in an ECC or it forces the manufacturer to adds an
>>>automatic sequencer so as to keep the costs under control.
>>>2). Those of us who do performance modifications would like to add
>>>larger injectors.  With the low cost ECC's you wrestle with a large
>>>minimum PW which complicates idle and emmisions.
>>>Ron
>>I thought that was what I was trying to say!! Sure, you need more
>>processing power and a faster processor to get smaller pw resolution. With
>>a bigger injector, you need a shorter pw (higher turndown ratio) to get an
>>idle that works. so you go to p&h injectors, but if you do not have fine
>>enough pw resolution,  you still do not get decent idle tuning. Like
>>anything else, you get to spend more money to do it right!!
>>>> Regards, Greg
>
>Wouldn't just using a lower fuel pressure work?.  So as to at least have the
>injector fully on?.  Do a rising rate device, rather than a
>1:1..   That one Bosch PWM FPR is beginning to sound better
>all the time.

>Bruce

Sure--adjusting fuel pressure will get you where you need to go to adjust
idle properly if you are stuck with big % steps in fuel delivery and pw at
idle. And this is a perfectly appropriate way to make do if tuning with a
cheap ecm (GM?).
My real points are:
That Hal-tek, Accel, and apparently Electromotive (see Espen's post) are
selling stuff that is nearly useless for street tuning if their pw
increment is 64 us!
That we should do our best to set the 332 project up to give really fine pw
increments--like 2us--there's certainly enough processore there to do that,
and this is a damn good reason to do so!!
That guys should be aware of the nature of the problem when deciding what
unit to spend their money on, and why they might just maybe want to spend
more!
That it is guaranteed that the only reason that GM spent the money to get
16 us pw increments (if that is really what they get) was idle emissions-if
they did not HAVE to have done it, they would not have!

I agree completely that mechanical injector (and fuel inertia) behavior
becomes a big factor at very short pw's, but without small enough pw
increment capability on the electronic side, we really do not have any kind
of an accurate idea of exactly HOW short a pulse is possible before that
factor takes over!

Given the large pw increment that the DFI/Accel ecu is stuck with, I quit
believing anything that they say about injector limitations!

Did not know that Bosch was making a PWM FPR--tell me more.

And tell Grumpy not to eat too much!!

Regards, Greg