Injector control

[Greg Hermann]

Hi guys--

A new thread. Bought a copy of the latest issue of "SUPER CHEVY" cuzza it
had a four page  article  on the Fel Pro SEFI 8 LO ECU in it. I know-and I
NEVER look at the pictures in "Sleazy Rider" either--!! [DUCKING!! :-) ]

Anywayz--in the article, they mentioned that the FP unit has an injector
pulse width RESOLUTION of 8 MICRO seconds--and bragged on this being far
better than a resolution of 64 mi. s. I kinda assume this to mean that the
smallest change in (adjustment to) injector pulse width which their ecu is
capable of making has a magnitude of 8 mi. s. and that (most likely their
competitors, brand A and brand H) other units can only make adjustments to
pulsewidths 64 mi.s at a time, no smaller.

This raised several questions in my little brain.

First--has anybody figured out how small an incremental adjustment to
injector pulse width time the OEM ecm's are capable of making (GM, Bosch,
etc.???)?? If so, is it posted anywhere??

Second, a few months ago, I talked with Lance Ward, the FP tech guy, on the
phone. He said (among other things) that they program their ecu so as not
to allow injector pulse widths shorter than 1 MILLI second. I assume that
this number presumes the use of p&h injectors, and that they have verified
that the p&h injectors work repeatably down to 1 ms. pulse width. But the
light bulb that came on is over the fact that an 8 mi sec adjustment to a
pulse width of 1 ms. would make a 0.8% change in amount of fuel
delivered--a reasonably fine adjustment increment when in a search for a
good idle. Whereas a 64 mi sec adjustment to a 1 ms pulse width would only
give a 6.4% change in amount of fuel delivered--way to coarse a
change--like, for example, you would have a choice of running 12.4:1;
13.5:1; or  14.3:1 mixture ratio at idle, and nothing in between- a
situation which would leave you without a prayer of getting a decent idle
if your injector pulse width needed to be as short as 1 ms at idle. And,
even if your idle (only) needed a 2ms pulse width, a 3.2% increment of fuel
adjustment is still too coarse an increment to do a REALLY good job of
adjusting things at idle.

I guess the apparent moral of this story, at least to me, is to temper any
info anybody gives you about how short a pulse width given injectors will
work with by asking how fine an adjustment to pulse width the ecu which
they are peddling will make!! And if you are putting together a setup which
is gonna use big injectors, and need a short pulse width to idle, you
really need to make sure that you are gonna use an ecu which will make
small enough incremental adjustments to injector pulse width too!

BTW--how small an incremental change in injector pulse width can the 332
project hardware make, and what level of attention is being paid to this
issue in the 332 project software??

There is a lot of room for comments here, so let's have at it!!

Regards, Greg