question for electrical engineers

[LCAM-01XA]

So we have this mystery black box. It has three pin connectors on it, let's call them pin A, B, and C. Here's the data I've gathered on this device so far:

a) box removed from truck and on work bench, resistances across different pins reads as follows: pins A<->B = 160k, pins B<->C = 120k, pins A<->C = 105k ohms.

b) box still removed, truck harness pins read as follows: pin A = 5V, pin B = 5V, pin C = ground.

c) box installed and plugged in, truck harness pins read as follows: pin A = 5V, pin B = 2.5V, and pin C = ground.

What do yall think is in the box? And what value resistors and connected into what circuit I would need to cause the wire harness pin B voltage to drop from 5V down to 2.5V, so I can toss the mystery box in the trash can once and for all?

 

[typ4]

tell us where the heck it came from and maybe we can help you.
I am guessing water in fuel box.

 

[Brianedwardss]

^ X2

 

[Dsl_Dog_Treat]

Wiper motor relay box??

 

[LCAM-01XA]

barometric sensor for E4OD

 

[typ4]

Having done some FI mods, I would leave it on and let it do its work. To much work to make it work properly without. It is basically a map sensor. Now if it would raise line pressure under boost that would be cool.

 

[LCAM-01XA]

Russ, it ain't quite like a MAP sensor to - the MAP sensor changes its readings dynamically all the time based on load on the engine, while the baro sensor only looks at ambient air pressure to guess altitude and somewhat alter the shift schedule (IIRC it pulls the upshifts a bit earlier the higher you go). Therefore if you only drive at one elevation most of the time, the baro sensor is all but useless, as it will always read about the same. This is my situation, I don't drive the truck much, and when I do I most certainly do not try to climb over the Rockies and then drop down to Pacific coast altitude (or the other way around), so the benefits the baro sensor offers to your regular slushbox user are not something I'm really keen on keeping - I'd much rather have the trans shift the same way all the time, much more predictable this way. And there is the reliability factor too, a simple resistor or 3 don't go bad all of sudden, while a faulty baro sensor can be hell to diagnose (read trackspeeder's comment in my E4OD odd issues thread) and in extreme cases I'd imagine that could cost a trans its life.

So after giving it some more thought I suppose I could rephrase my initial question - given two 5V inputs and one 0V ground, how do I make one of those 5V to drop to 2.5V? Resistances I measured in the black box probably don't have much importance, since I ain't after duplicating their circuits or anything - all I want is to cut one of those 5V in half, nothing more...

 

[rhkcommander]

Figure out the amperage, then slap a resistor in there... or divide it to two sources

 

[OLDBULL8]

[So after giving it some more thought I suppose I could rephrase my initial question - given two 5V inputs and one 0V ground, how do I make one of those 5V to drop to 2.5V? Resistances I measured in the black box probably don't have much importance, since I ain't after duplicating their circuits or anything - all I want is to cut one of those 5V in half, nothing more...
__________________
/QUOTE]

Ohms law.

 

[LCAM-01XA]

I don't what that current is, or even where to measure it - I thought the middle wire of the baro sensor is the signal return to the PCM, and then all of sudden found that the damn thing actually has voltage on it already - so whatever little I know about voltage dividers went right out the door there... In that situation, with two inputs and one ground, how and to what do I apply Ohm's law? (I was never very good at that class, barely got a C there)

 

[OLDBULL8]

LCAM-01XA

Hijack: Hey, can I use that Avatar of yours? Want to make a vinyl copy of it and put it on my garage door. Is it copyrighted?

 

[LCAM-01XA]

Oh yah, the avatar is probably copyrighted, the company makes all sorts of products with that motto (and others too): http://www.bustedknucklegarage.com/

 

[jpw]

in general ford BARO/MAP sensors output freq based on pressure. general rule 158Hz @ sea level/ 104hz @ 18"Hg.
No engineer just a mech HTH

 

[LCAM-01XA]

JPW, now that you mention it, I do seem to recall running into that whole frequency mess on an EEC-IV passenger car... so the black box is not just resistors, but some sort of frequency generator? Well there goes my plan for simplifying things...

Brian, that's what I meant by a voltage divider, that's essentially what a potentiometer is - a variable voltage divider. With those those one of the connectors is an output, and so the wire for it would have 0V with the black box disconnected, but this is clearly not my case where I have 5V on both non-grounds, and the box somehow drops one of them down, but not based on resistance alone.

 

[jpw]

LCAM freq gen is correct, signal wire should allways read 2.5v until you switch your meter to Hz. whats wrong with the original one?