Re: Ford injectors (& Question)

[Roger Heflin <rah@horizon.hit.net>]

On Fri, 18 Aug 2000, Dave Zug wrote:

> I have a few notations and a question after reading this thread.
> 
> I have a set of 28# stock GN injectors if anyone wants them. $35 + shipping.
> I bought them off ebay, no guarantees but the guy said they were 80k miles
> and good.
> 
> The SVO's I DO have, but not installed in the 383 yet. I knew they were
> rated at less pressure than the GM's but now I know 39 psi is the test
> pressure.. Thanks.
> 
> A friend has SVO's in his ZZ4/HotCam TPI... one clicked and he replaced it..
> no more clicks. He may pipe in to revise or extend my remarks..
> 
> My stock L98 injectors in the TPI 383  run 11+ ms w/ 48 psi fuel pressure at
> idle, vac off. (just notes for comparison)
> 
> 
> To the question... at 6000 RPM, it is 20 ms, not 10ms between the time an
> intake valve begins to open until THAT intake valve begins to open again.
> (100 crank rotations every second = 50 cam rotations = 50 valve cycles, but
> you know that) Specifically for the driver configuration on the 730 and 165,
> someone please tell me why 10 ms is considered static. Is it that a driver
> is toggling between 2 banks of injectors and is only able to fire any one
> bank for 10 ms?  I'm sorry to NOT have this clear in my mind after years of
> twiddling and reading.. but I'd like it clarified one more time please and
> thanks.

It is 10ms for a batch fire car, they fire it 2x a sequentail
car for only 1/2 of the time.   They are (at WOT) firing both banks at
the same time, but only for 10ms instead of 20ms. and they will fire
twice for injector time listed in that 20ms.    Most of the batch fire
cars seem to work this way, the seqential ones don't, and work the way
you described.   I believe the big reason is that that is the way GM
decided to do things.   

>From notes on other car computer (aftermarket) the injectors won't
close in less than about 1ms, so if you don't have the injectors off
for more than 1 ms the injector wont ever close, and will go static
(alwasy open).   At 6000 rpm this means that somewhere around 9ms and
the injector will go static.    THe basic problem is the coil takes
time for the field to colapse, and the bigger the coil (given the same
electronics) the longer it will take to colapse, and if the field has
not colapsed yet when the injector reenergizzes, then it will open
much faster that a fully closed injector, so you would be getting alot
more fuel than the given PW will claim, and the less it is actually
off the faster it will reopen, or possibly not even get closed.   The
problem is really that at some point before full current flow the
injector is fully open, and the rest of the current flow just adds
more momentum to undo when you close it.  It is kind of like a hose
faucet you can turn is to fully open, and then even go a turn or two
more and not increase the water flow, but you do increase how many
turns (and time) that it takes to turn things off.  The big problem is
it is much simpler to turn things on full (all the way) that to
exactly determine when it is really fully on.
 
Most computer gate electronics also do this, and it means there is
some momentum to overcome to turn things on and off, and if you  time
things too fast they will never actually change state.  There is a set
of computer electronics that don't do this (ECL) but they are quite a
bit more complicated to build and work with.

				Roger


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