Electrical testing; nothing makes sense...

[Insanejughead]

Two years ago my pickup was involved in a wreck. In order to have something to drive, I took the '86 thunderbird turbo computer and components that were in the ranger, and I swapped into back into my '86 thunderbird. I then put all of my '87 turbo coupe stuff in the ranger, but it won't run correctly, no matter what I do.


From what I've found out, the '87 LA3 has a few differences in wiring pinouts.

Pin 25 = Air Charge temperature sensor (lower intake manifold)
Pin 27 = Vane air meter (Air Flow, specifically)
Pin 43 = Vane Air Meter (Air Temp)


However, no many how many times I check the outputs of the computer connector with the devices that the wires lead to, there arises an issue I'm unfamiliar with; and no matter what I do, it is still there.

When checking the output of all the sensors to ground, and all that, I get 5 volts on EVERYTHING! However, when I test them between their respective pins to Signal Return, I barely get any voltage whatsoever.

Now, like I mentioned in the "Electrical Mystery" thread in the Turbo specific forum, I redid my ENTIRE harness. For the past month, I've went through every single wire that leads between sensors and computer and elsewhere, but still cannot find anything that is awry.


Testing things in the EXACT same manner on my car turns up differently. My car runs perfect and gets 28-30 mpg.


So... What is going on with the sensors and/or computer? This problem has been here all summer, and I'm at my f*cking wits end on trying to diagnose and figure shit out.


On a side note, using the self-test connector comes up with nothing. I can't get any codes out of it. I have wired it several different times with using pins 28 and 48, but never have I been able to get codes out of it, so resorting to it won't help me. Also, searching brought up loads of vague information that isn't specific enough to help me out in any reasonable fashion.

 

[killj0y]

What are the specifics I cab check all data to see if they have a weirding diagram, it might help

 

[Insanejughead]

What are the specifics I cab check all data to see if they have a weirding diagram, it might help

Sorry, but the way you worded this just doesn't make sense to me, bro.

 

[--weezl--]

he asked what the specifics of the truck are, he's going to check alldata to see if there's a schematic for your vehicle

issue with that is it's an atypical installation...



imo, if the computer in the 86 is the same pinout as the 87, just swap computers and see what happens, it will tell you if it's a truck/wiring/sensor error, or if your ecm or what be it, is pooched...

 

[Insanejughead]

he asked what the specifics of the truck are, he's going to check alldata to see if there's a schematic for your vehicle

issue with that is it's an atypical installation...

Okay. I have four sources that I've been using for pin-outs on this application, but if you can get another one, that would be cool.

I'm dealing with an '87 Turbo Coupe LA3 computer.

imo, if the computer in the 86 is the same pinout as the 87, just swap computers and see what happens, it will tell you if it's a truck/wiring/sensor error, or if your ecm or what be it, is pooched...

They aren't the same. I thought they were, at first, except for one pin, but since I've made the mistake of having the wrong sensors being pinned into the computer differently, I don't want to try the LB3 that I have on hand, for fear of possibly ruining it. After it wasn't running right, that's when I discovered that the pin-outs were in fact, different (total of 4 pins difference)

The pins that are different are: 25, 27, 31, and 43.

 

[Insanejughead]

I've been messing with this thing daily, and I STILL have made no progress.


I've been wondering if my ECU is going bad? What is a DEFINITE way to figure out if the ecu is bad or good?



Why does checking voltages not work for me?

With the key on, but everything disconnected, I see no voltage on pin 46 (Sig Rtn), yet any time I plug something into the circuit (e.g. TPS, BP, ECT, VAM, ACT) I see nearly ALL of the voltage on my Signal return wire.

Example: Pin 26 (VREF) has a steady 5.17 volts on it. When I plug the VAM in, the signal return wire shows all of that voltage.

ECT (pin 7) has almost 5 volts coming out of it, and when I plug it in, Signal return shows all of that voltage as well.

Same goes for the TPS (it's new). It's the weirdest one of all, honestly. Even with it being the only thing in the circuit, probing its wires with the key on shows just above five volts on ALL wires. I know that isn't right because it should have ONE steady incoming voltage signal (26, vref), and two changing voltage signals (as signal return goes down, TPS goes up.)


However, PLEASE correct me if I'm wrong.




Back to the ECU thing, I wish that I had another LA3 to test in my ranger, but I don't. I do have an LB3 to use if I could only find the damn thing, though.



I need input, please! Suggestions (if I haven't tried them) will be considered





Oh, and I double and triple checked my test connector's wiring with my schematic, and I'm still not able to see any codes out of it. The only thing that happens is my fuel pump relay clicks, and my CEL stays lit, with no fluctuations....

 

[Insanejughead]

Nobody has any ideas?...

 

[--weezl--]

Borrow a junkyard one?


Sent from somewhere naughty!

 

[Insanejughead]

I would have already if a junkyard near me had any turbo coupes; I would rape any turbo coupe for parts if I could find one.


I also cannot locate my LB3 (I thought it was a 3, but it might be a 2; it's been so long since I've seen it, that I could just be telling myself to think that it is.)

 

[Insanejughead]

Is there any way to test the entire computer on a diagnostic machine? Does Ford do that; or any shops?


Would anyone be willing to test my computer in their own vehicle, granted, as long as theirs has a good and solid wiring configuration?

 

[dieseldane]

As far as the sensors being 5 volts, that's not a problem, a lot of sensors only run off that, now getting 5 volts on the return signals all the time and 5 volts on everything else, that doesn't sound right... Have you checked the pin locations on all the plugs (other than the ecm) as well? They vary from year to year also.

 

[Insanejughead]

Yes, I have. That's why this is becoming a total mindf*ck to me. I've downloaded and checked my setup against half a dozen of my dad's electronic engine system books, on top of what repair manuals and schematics I already had.


My ranger was wired to match the '86 PK1 computer back in 2008. Then, this summer, I put the LA3 in it; it didn't run, at first, but then realized that I had to add in the wires for the ACT, as well as swap the pins that came off of the VAM. Well, it STILL didn't run right. That is when I started testing each sensor individually, which led to me completely removing the wiring harness and going through it, inch by inch.


And now I'm here. Confused as hell to why it isn't working, and one computer shy of having it work right.

Btw, I thought that when computers go bad, nothing works... I'm going to venture out on a limb and say that isn't so, anymore, is it. Or is it?

 

[dieseldane]

The only computer I've ever had go bad on me was in my old accord back in high school, and then nothing would work at all.

 

[Insanejughead]

The only computer I've ever had go bad on me was in my old accord back in high school, and then nothing would work at all.

That's what I thought would happen in my case, but it runs.



Just badly... So, what is going on with the computer?

 

[adsm08]

You told us what the different pins do for the LA3, what do they do for the LB3?

If too much juice went to it you may have done damage. The VAM may also have been damaged.