Re: P&H Injector Interface

[garwillis@msn.com (Garfield Willis)]

On Sat, 20 May 2000 19:36:33 -0400, "nacelp" <nacelp@bright.net> wrote:

>Pg 182 shoes the late truck ecm connectors (Drk Rd-Drk Blue)
>...
>12089660 Terminals

OK, if you're saying the ecm connectors are MicroPack connectors, then
the terminal part no. you have above (12089660) I don't see in the
catalog (btw, where'd you get that #?). The female MP terminals are on
pg. 172, along with all the currently available housings. Most of the
other numbers you quoted aren't in the catalog either, nor in the
cross-reference. That's no biggie if it's just the color of the plastic
that's involved. They often made color specials for OEM usage. But the
fact that the terminal numbers don't correspond has me still a tad
worried. Have a look at pg. 172, and see if those terminals are indeed
the females we're seeking, and you're using.

>What I thought was 727 terminals were wrong, I can't find them anywhere in
>this catalog

Hmmm, wonder if on those they used someone other than Packard as
supplier? Gawd, why would they DO that?

OK, Segue back to another erstwhile issue:

...if these GM ECM terminals we've been discussing are indeed MicroPack
connectors (which I trust they are), be aware that the nominal rated
current per circuit on the MPs is 5A. Hence my concern about peak
currents when driving 4 P&H injectors thru them. When driving one TBI
(1.2ohm 2mH) injector on such a circuit, this is just within parameters
(it might not look like the math is right, but the 1.2ohm injectors are
sposed to have a nominal current-limited peak of around 4.5A, and a hold
current around 1A: remember you have to consider the inductance as well
as the resistance), and would be equivalent to driving two (2) TPI
(2.4ohm) injectors, but I think driving four (4) TPI injectors puts you
over the top. [With sat injectors (12-16ohm), you can see how you can
drive considerably more of those injectors together thru one such pin].

Now, mind you, you CAN "get away with" that, all that happens is the
terminals get warmer, and the contact resistance goes up, and the
low-side load floats up a bit. But in the long run, it's considered bad
practice to exceed these ratings, because outside it's design limits the
terminal is corroding from the heat, stressing from the thermal cycle,
and the injector solenoid isn't pulling in quite as firmly as it would
have normally, due to the increased resistance. All not-so-good
downsides. This is all on a continuum tho; just be aware you're skating
on thinner ice when you hang out on the hairy edge like this. The curves
on all this bad stuff mentioned above, go up very rapidly outside the
design region. That's how they decided what IS the design region for the
connector pin. :)

Makes we wonder more about the wisdom of retrofitting new higher-power
drivers directly into the ECM box. All that extra drive current has to
go out those wee pins. Better to take an injector "signal" from the box,
and let the bigger external drivers handle the extra load with
better/bigger contacts (not to mention bigger ground returns) on their
own side. That'd be my take. Guess I'm getting leery of this "secondary
ECM connector idea", especially if we're still talking about driving 4
P&H injectors thru one pin. Hey, call me paranoid, call me
overly-cautious, but don't call me if months down the road, during some
critical race, your connectors start to smell and get intermittent on
ya. In fact, driving 4 (2.4ohm) P&H injectors thru one of these pins is
far enough over the edge for me that I think this is where I get off the
train.

I think bigger connection pins are in order for these conversions. Just
me dos centavos, amigos. Back to the intrusive wire splice. Sorry Eric.

Crumbs, why do I have to always play the part of the Ogre? Whimper.

Gar


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