Do you or your repairman have access to an oscilloscope - something that will let you look at a waveform? It would be nice to see exactly what that SPOUT signal looks like.

And with the FP relay NOT hot-wired (KO), what's on pins 40 and 80? And with the FP manually grounded?

 

What is on the other end of pin 40 (FP Monitor)?

This could be the answer to just about all of it.

Oh, and my repair guy just bundled up my truck so I can have it towed somewhere else.

 

From your battery, there is a fuse, then goes to fuel pump relay.
Pin 80 from PCM turns on/off the fuel pump relay.
The power from relay, then goes to the fuel pump(actually, inertia switch first).

Pin 40 is an input, that is also tied to the wire that goes out of fuel relay to fuel pump, hence "FP monitor".

 

Here is the diagram to match the previous response

 

Thanks very much, rla2005.

This chart confirms the pin 40 FP_MON connection.

I found this here(https://web.archive.org/web/20110414...on.com/?p=64):
The EEC needs to senses several things to start an engine:
* Power to EEC and fuel pump(s)
* Slow and irregular PIP signal from the distributor
* MAF/MAP low and irregular
* TPS is closed
* HEGO shows lean

So, if I have no ground at pin 80 from the PCM, I'm dead in the water. Is this correct?

 

That is correct. The fuel pump relay will never energize.

 

Thanks, rla2005. That's what I thought.

Also, there is 12V and ground at the data link connector, but My guy's scanner shows Communication Error.

 

I just reread this whole thread, seems like the consistent problem has been that the fuel pump relay needs to be manually energized to make the truck run. There is an obvious problem with the original PCM and there is no evidence that anyone let the smoke out of the 2 replacements PCM's. I presume you are activating the fuel pump relay by grounding the test point, which is the same as the PCM applying a ground to the relay coil. I did not find any mention of the fuel pump relay operating for 1 second when you turn the ignition on.

The fuel pump relay is energized by the PCM, (via a switched ground) for 1 second when the key is first turned on. Internally, this starts a 1 second resettable timer that will time out, releasing the fuel pump relay control ground. The tach pulses keep the timer reset, thus keeping the ground on the fuel pump relay if the engine is cranking or running. If the tach signal is not present, the fuel pump relay ground will disappear, shutting off the fuel pump. That's the simple version of how the fuel pump control circuit works.

The 1 second operation provided when the key turns on should be part of the diagnosis. If this happens, the PCM is working correctly. The fuel pump relay will shut off if the engine is not running, or by extension, if you lose the tach signal. The relay will stay energized if the engine is cranking or running, (with the tach signal present).

Just a few thoughts I had, perhaps they will help.

 

Yes, that is VERY helpful.

I'll definitely tell the guys at the whichever shop near me where the truck lands next.

As a side note, I had the absolutely best lobster bisque ever at the restaurant at a Holiday Inn in Saskatoon in the late 80's.

 

1) A few comments on the art/science of troubleshooting, which apply whether the subject is biological, mechanical, or electrical:
- You must have the discipline to follow a logical procedure, usually starting from the foundation up (pulse? breathing? all power supplies up? clocks? is there a spark? fuel reaching cylinders?), and not go galloping off into the weeds over distractions as they inevitably appear (SQUIRREL! Satan! The damned Fed, again!).
- Once the basics are checked, use the symptoms to form and test a hypothesis. Modify and repeat, with each cycle eliminating more and more of the problem space.
- Be very careful to minimize your assumptions, and either verify them before drawing any conclusions or clearly mark those conclusions as suspect and conditional. Take notes and stay organized.
- Along the way, fix what you find out is broken even if you don't think that it explains the symptoms (and don't be surprised when that turns out to be the problem).
- If you can't get to the problem by deduction, try the process of elimination.

2) Scanning for codes from the PCM is an early step in most engine malfunction troubleshooting procedures. That the scan port is dead is a MAJOR PROBLEM. It is a 'day 1' problem. And yet that's not the only thing pointing to a PCM issue: it's the PCM's job to turn on the FP relay, but that's apparently not happening; and, the original PCM suffered some catastrophic failure (possibly taking out other components/wiring in the truck).

This is not a logical conclusion. That it would start without the PCM supplying SPOUT says that it isn't actually even needed to for this particular ICM/engine combo to run. SPOUT just being stuck high or stuck low could be enough for the ICM to change timing - or it could be due to something entirely different. Putting an Oscope on SPOUT would let us see if it's really pulsing, hence the question asking if you had access to one.


3) This is a good spot in the process to stop with other pursuits and get the PCM talking through the scan port (which has a pretty good chance of taking care of the FP signal at the same time, and probably some other problems that aren't even yet visible considering the truck's state). In looking over what schematics I have for '96 OBDII trucks, it looks like the only place that the scan port's data lines connect to are the PCM, so that means finding out what's stopping the PCM from talking.

Approach A) Deduction - start with the basics, the foundational operations:
- You haven't mentioned the behavior of the CEL during start - exactly what, if anything, is that doing at KO and at start?
- subford asked about verifying power on some pins, I've also asked about the same pins and several more. You have a beautiful breakout box that makes those measurements very, very easy. Please measure and post all of those measurements that have been requested.
- subford also mentioned 5V out. In looking at the OBDI schematic, which is only indicative what might be on an OBDII board, that same 5V is also used to run the ICs on the PCM - if something's wrong with that 5V power supply, the PCM will have big problems. As already mentioned, the fried portion of the original PCM had some indications that it was the area that generated the 5V supply. Pins J3-1 and J1-90 are that 5V supply. Absolutely do not try and hot-wire this like has been done with the FP relay.
- Check for continuity/shorts/etc from pins 15 and 16 on the PCM to their respective pins on the scan port.
- The over-currents in that fried PCM were substantial. Take the time to check each and every fuse in both fuse panels (KO; use a VOM, ground the neg probe, see that there's voltage at both exposed pin-tops on each and every fuse). Electrical over-currents are like roof leaks - where they come in relative to where they go out can be quite bizarre; it's a simple, low-effort test that could save you a lot of grief (discipline: suffer a little now to avoid suffering a s*** ton later).
- These are just the first steps in the process of this deductive approach. The results from these steps set up the next set of steps.

Approach B) Process of elimination (a last resort, only to be used if deduction fails):
- Something fried out the original PCM. Since multiple replacement PCMs don't appear to be working, there's obviously something else wrong with the truck that's got some relation to the PCM.
- Imagine if you could operate just the PCM and scan port in isolation from the rest of the truck. Assuming it then came to life - and complained bitterly about all kinds of things not working (since it's not connected to them) - you could start adding back signals to/from the truck (always with the power off before making a connection) and see if it's still alive. At some point, something that you reconnect will cause the PCM to stop talking - obviously, that's your target.
- As a compromise, you might be able to disconnect enough connectors here and there to approximate this isolation, though you'd likely have to manually supply some voltage and ground connections to the PCM (all listed on its pinout - fuse all such supplied voltages). Even if you disconnected all of the connectors you could think of and it was still silent, that's valuable information in that implies that the problem lies in what is still connected, thereby reducing the problem space. Use the PCM's pinout to make a comprehensive list of all connections, cross them off as they are eliminated; for those you can't/don't disconnect, list these out and tackle them individually.

 

I think it's important to remember that the OP has a 3rd party doing the work on his truck. I suspect the OP has a pretty good understanding of the basics and one could safely assume that the basics have been checked. It would appear that at this time, the mechanic has given up and handed the non running truck back to the OP who now must find another shop.

We all have our own methods of troubleshooting and I'll admit I have some concerns about the method laid out in BWNG's post, but what do you hope to gain by measuring the internal +5V bus? Surely, the processor is running as the truck can be made to run under certain conditions and a failure of the +5V bus would mean a dead processor and a dead truck.

 

Thanks so very much to all who have shared of their considerable expertise on my behalf here.

And to BWNG and NET2014 a very special thanks for the time you've put in for me. I am humbled by the depth of your understanding of the inner workings of these systems.

My truck will likely be back in my hands again today (11-6) or tomorrow, and I will get the breakout box going again and check the status all of the pins mentioned, starting with the DLC connectors.

Can someone post a link to a definitive pinout chart for my EEC-V? I'm using a couple of different ones that each seem to partially agree with the pin numbers you guys have shown, like ECU Pinouts / EFIDynoTuning

I have ordered a 1996 OBDII Powertrain Control/Emissions Diagnostics manual on eBay, but I won't have it for a few more days.

-Jack (retired computer programmer in central Texas who is clearly in over his head in a hardware problem)

 

PCM Connector C1027 Pages 1 & 2

 

For checking the PCM, this is one of the basics: in general, the first thing to check on any board with problems is power supplies and clocks. The one clock is just a crystal hanging off of the microcontroller, and we can't get to that anyhow. The only generated power supply on this board appears to be this 5V.
Note that there are a whole spectrum of conditions it can be in, not merely '5V' or '0V'. For example, when the original PCM fried, that could have put some high voltage on this line and created any number of problems downstream somewhere in the truck: short to some other signal, ohmic bridge go ground, ohmic bridge to VB+, short to VB+, etc.


We're still in that 'darkness' phase of troubleshooting where there are a collection of symptoms that don't yet make sense and more data is needed to get some resolution before making any solid conclusions. While the PCM is at the nexus of a number of problems, they don't necessarily mean that it's fully dead - like with the 5V supply, there are a whole spectrum of conditions between fully functional and dead.

Regarding the claim that the PCM's SPOUT is working:
- The truck won't start with it connected, and assuming that it's wiring is good, then the PCM isn't putting out a valid SPOUT at start. Again, this points to some problem in the PCM.
- From the 1996 Ford Powertrain Manual, in the block on the Ignition Control Module: " ... Based on input signals, the PCM will signal the ignition module to make corrections to the basic ignition timing..."
... so it sounds like the PCM isn't timing the sparks, it's providing a 'correction' signal to the ICM and the ICM itself has some basic ignition timing that it implements. Conceivably, once the engine is running - bypassing the PCM's bad SPOUT at start by disconnecting it - whatever is on SPOUT afterwards isn't enough to prevent the ICM from supporting ignition on its own.

A bigger mystery to me is how the cylinders are getting fuel, but again, we're still in that 'darkness' phase of troubleshooting where there are a collection of symptoms that don't yet make sense and more data is needed to get some resolution before making any conclusions. Maybe there's some lower-level circuitry supporting that too, much like the ICM is apparently running the ignition on its own.

Assuming that the replacement PCMs remain good (as yet unproven, but plausible), somewhere in that truck is something that is preventing the PCM from fully normal operation:
- The scan port isn't working, and its data lines come straight from the PCM and go nowhere else
- The signal from the PCM to turn on the FP relay has a problem (not yet measured at the PCM, so could still be wiring)
- SPOUT from the PCM isn't valid at start
(- no report on the CEL's behavior at start, but another easy test of PCM health)

 

rla2005, thanks for the pinouts.

- The signal from the PCM to turn on the FP relay has a problem (not yet measured at the PCM, so could still be wiring)

My repair guy took the entire PCM harness apart and verified continuity on EVERY wire end to end, including pin 80 to the fuel pump relay.

He also cleaned several corroded connections in the connector that goes to the PCM.

The engine only runs when the FPR is manually grounded.