Either way, transistors work off of current, not voltage.
I've always known them to 'drive', so the chip uses 5v and a small current to enable the output, which is a proportionally larger current. and since it's driving, it is outputting higher current to enable the injector(s).
I really doubt that the injectors are hot all the time, and the transistors ground to enable.

Those transistors OUTPUT lots of POWER, which are in the PCM.

 

And that would be absolutely incorrect. The injectors are at +BATT potential and the PCM provides a ground to fire the injectors. And FWIW, free electrons flow from the - potential to the + potential. Basic electric theory here.

But really, there are a lot of good resources being used here for petty arguments. Let's try to stay helpful.

 

Thank you for correcting me, I should have looked at a schematic.
So, yes, Injectors are powered +12V all the time, and the PCM transistors ground them to enable.

 

That is absolutely correct

And that's correct too - power couldn't get to it's target without the (full amount of) current flowing through the PCM: current flows in a circuit, whether one chooses to follow electrons (- to +) or (more imaginatively but mathematically identical) the holes where they once were (+ to -), and the PCM is in that circuit.

 

1) Is the J3 port on either of these two PCMs accessible? If so, and assuming that the J3 pinout is the same as on the EEC-IV PCM, you should be able to measure the internally generated 5V on pins J3-1 & J3-2 (with the PCM plugged in and powered up; VB (battery, 12V) should be on J3-27 & J3-28, and gnd on J3-29 & J3-30; for reference, you can see the pin numbers printed on the board around the J3 connector on your fried PCM). I don't know how this 5V line would look if something external to the PCM was pulling it down - if there's something internal to the PCM to block that from happening or not - but it's worth checking.

2) Referring to the first photo in reply #36 (the top side of the fried PCM): Along the top edge of the Printed Circuit Board (PCB), near the left end is a spot marked Q47, with one of the vias marked B (for base), another E (for emitter), and the third one looks to be unmarked in this photo (would otherwise be marked C for collector) - this is a spot where some optional transistor, Q47 would go if your board needed it, and is useful for seeing how the board would be marked around a transistor of the same type.
Along the bottom edge of this photo on the far right, under the right most black clip, I suspect that there is an actual one of these transistors, with the PCB marked Q1 here (correct?) and the outer two vias marked B & E with the center one unmarked (just like at Q47's place; also correct?). If all of that is correct, does the center via (the transistor's collector) have continuity to J3-1? Are there markings on this transistor itself?
On the right edge of the board at the bottom, there are two transistors hidden behind black clips. The PCB labels for each of these starts with 'Q1' but then the next digit or two is hidden by the black clips. Are there any markings on these transistors?
Is anything that was under the black clips visibly fried?

I'm wondering if the fried components might belong to the circuit that generates the 5V supply for the rest of the board and whatever else external needs it. The reason for this is that while I haven't been able to find a schematic of an EEC-V PCM, I have stumbled on one for an EEC-IV PCM and assuming that the general architecture is carried over (and expanded), the 5V generation circuit on the EEC-IV schematic is the only circuit that uses a few small diodes and transistors - and the fried components are the only collection of a few small diodes and transistors on your PCB (Q89, Q90, Q98, D149, the diode to the right of D149, plus the two formerly-yellow caps below Q90 and Q98 (there's an unmolested cap like these on the right edge at the top)) - but I'm largely guessing.

Some random EEC-IV schematic. 5V generation circuit top left. This has an Intel 8061 at its heart; yours has an 8065 (largest IC on the PCB; has '8065' in the first line printed on it). Note how the collector of Q10 (on the sole wire marked in red) goes directly to a pin the main connector, J1 - this is that 'switch by pulling down' mechanism already discussed).

 

BWNG, thanks for your extensive research on my behalf.

I have just found out that after starting the engine with the SPOUT out and then plugging it back in, the engine runs and the timing advances. This pretty much verifies the computer controlled ignition and fuel pump operation post-relay.

This is with the fuel pump manually grounded because the PCM is not providing ground to the FPRelay.

Apparently, the crux of my problem is causing the failure of the FPR ground from the PCM.

We have tried 5 different PCM units from 2 different vendors and they all did the same thing.

ALL of the fuel pump PCM wiring has been verified as operational, as well as all of the other fuel pump connections, because it does run when manually grounded.

The ignition switch wiring has also been verified and eliminated as a problem.

Also, the ODB-II connector is reporting communication error. Could this be a clue?

My repair guy is about to give up, and I don't really know where this is headed next.

Any ideas?

Thanks very much to all of the responders who are truly trying to help here. I appreciate it very much.

-Jack (running out of options in central Texas)

 

Communication error could be your scanner, wiring in the OBD2, PCM failure, possibly shorted sensor.

If SPOUT is disconnected, is your timing at 10 degrees?
Still doesn't explain fuel pump issue.

It's gotta be a shorted sensor, bad ground somewhere, wires crossed somewhere, hopefully not more fried PCMs.

Smell them, if they are fried, they will stink.

 

Fuel Inertia switch open or closed, reset?

 

With the key on, what is the voltage at pin J3-1 of the PCM?

 

WW, SPOUT in, timing is at 10 degrees.

SPOUT out, timing advances.

I don't think the PCM is fried because the engine runs under computer control.

Inertia switch is closed because engine runs.

<< It's gotta be a shorted sensor, bad ground somewhere, wires crossed somewhere. >>
I totally agree. How do I proceed? My repair guy has spent the better part of the last 2 months looking for just about anything out of whack and so far has found everything he's looked at to be totally nominal and as expected.

 

BWNG, where do I find pin J3-1?

The rebuilt PCM is installed in the truck.

 

J3 is the bus port which is accessed thru a small removable window located along the side of the PCM. Honestly, I am not sure the OBDII versions even had the port.

Testing my memory even further, I recall the ground supplied by the PCM for the fuel pump relay control may not be the main ground for the PCM. Lacking a '96 wiring diagram, I can only advise that all the grounds required need to be hooked up. This was something I discovered by tracing the circuit through the printed circuit board of the PCM and that, very likely was on an OBDI application. Long shot, but it may be a clue.

 

Look at the first photo in your reply #36; the top side of the PCM's PCB. The connector on the right edge is J3, where 'the label J3' is printed on the PCB; 'J3' is also printed on the back side of the PCB. The odd numbered pins are on this top side of the PCB (and even on the back - look at J3 on both photos), with J3-1 at the top of this first photo.

 

... also, after a few minutes of operation is any side of the PCM hot (in particular, the corner at the bottom right of the first photo in reply #36)?

 

If you haven't tried getting to J3-1 yet, it looks like the same signal can be gotten to with your breakout box: what's the voltage on pin 90 (key on). Might as well also measure pins 71 and 97 while there - and you should have good, solid grounds on 23, 24, 25, 51, 76, 77, and 103. Pin 91 should at least be close to ground, if not at 0V.

A schematic of a ML1-4XX PCM would be ideal to have, but is probably not obtainable. I do have a copy of the 1996 OBDII Powertrain Control/Emissions Diagnostics manual, though, and just dug it out - it's about 5" thick.