Re: P&H Injector Interface

[garwillis@msn.com (Garfield Willis)]

On Thu, 25 May 2000 23:40:02 -0700, "Walter Sherwin" <wsherwin@home.com>
wrote:

>The most probable DIY-EFI injector ?conversion? configurations that I can
>think of would be:  1) SEFI MPFI  SAT to P&H ? assume a max of  8 inputs and
>a max of  8 injectors.  2) BATCH MPFI  QUASI P&H (current sharing ganged
>pairs) to individual P&H ? assume up to 2 inputs and a max of 6 injectors.

Whoops gotta go slow here. Why SIX? Or do you mean 6 total, a max of 3
PFI injectors per driver/input?

>3) BATCH MPFI  SAT to P&H ? assume 2 inputs and a max of 8 injectors.  4)
>Single Channel TBI to Dual Channel TBI ? assume 1 input and 2 TBI injectors.
>5) Dual Channel TBI to 4BBL TBI ? assume 2 inputs and 4 TBI injectors.  6)
>Dual Channel TBI to twin 4BBL TBI ? assume 2 inputs and 8 TBI injectors.

Good Golly, are you SERIOUS? You mean to suggest 4 1.2ohm injectors per
driver? for a total of 8!!? OK whose got such a beast wired up? That'd
be 16A peak current on a single harness wire. I don't believe it!

>Every one of the individual injectors listed above, can be safely driven via
>one individual 4/1 amp current driver per injector.

Yes, close, but that's NOT even the problem. OHHHH if only it was, Walt.
The problem is that nobody want's to rewire their harnesses to run an
individual wire up and out to each injector. Neither the original TBI
harnesses, nor the Batch PFI harnesses, have more than the two wires
coming from the ECM and going out to the injector's loom.

THAT is the crux of the problem. If we need to stick to the original
harness, then the drivers have to be capable of driving multiple PFI's
and TBI's *on a single wire* or two, namely the original harness
wire(s), which is the way they're presently wired. In the batch
harnesses, there are at most TWO wires going out of the ECM and up to
the engine, where at some point they get split out to the individual
injectors. But not at the ECM.

There is also another problem with this scenario which I'll mention
shortly.

>Soooo,  how about a basic driver box housing 8 individual 4/1 amp current
>drivers?   This would cover every probable conversion configuration.

Nope, I don't think that dog will hunt. You can't just wire these
drivers up in parallel if you need to drive more than one injector on a
single wire. That's the problem. Your scenario must either assume that,
or additional wires from the interface out to the individual injectors.
The present pair of wires in a batch-fire harness IS able of carrying
the current (not the ECM pins, but the wires are OK; we would splice
into the two wires outside the ECM).

Yes, it *would* be absolutely trivial to create a module containing 8
individual TBI drivers, or 8 individual PFI drivers, or whatever. And
the former is what's needed for SEFI applications, but for batch-fire
ecms...

The issue is, how do we practically drive multiple PFIs and TBIs on the
SAME wire. Once again, that raises other questions about that VIC box.
I'm beginning to wonder if that box actually ASSUMES a re-wire of the
injector loom? If it does, it's not only whimpey and pricey, it's also
unnecessarily intrusive. Geez, it was bad enough suggesting to guys that
they break into at most two wires outside their ECM, but the idea of
insisting on them wiring a bunch more individual wires out to their
engine harness is WAY over the top, at least to me.

Now, here's the other problem with your conjecture that "8 individual
4/1 amp current drivers would cover every probable conversion
configuration". You CANNOT safely drive a single PFI with a TBI driver.
The reason is that with the TBI driver with it's higher peak and hold
current limit settings, (1) the PFI may not reach the peak TBI current
and proceed to current foldback; remember a PFI has twice the resistance
and inductance of a TBI, so it's intended peak current is 2A, not the 4A
of a TBI driver. Simply put, you put a 2.4ohm injector on a driver that
expects to get up to 4A before folding back to it's hold current, and it
may not get there in time, but (2) suppose that poor PFI ends up drawing
all the way up to 4A eventually, and tripping the driver into it's
"hold" mode. BUT what's the hold current now? 1A, not the originally
intended 0.5A of the PFI. You stressed it to peak, now you're stressing
it in hold mode. Not good.

I appreciate the suggestion, unfortunately it's not really a workable
solution, AFAIK.

Gar


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