There can be problems with input signals that lead the computer to shut down the engine by not firing injectors. One that I've dealt with was a degraded PIP signal when the engine was warmed up - it looked fine on an Oscope, but the PCM didn't like something about it and stopped firing injectors. There are probably others (e.g., TPS output shorted to VREF).

The CEL came on and the PCM gave out a code that pointed to the PIP sensor, but I didn't want to change it out since the output looked fine and it's such a PITA to replace. Then I came across a youtube video where some automotive class was dealing with the identical issue and the class instructor said that he'd seen seemingly-good PIP signals cause the PCM to throw a code and stop firing injectors before, so I pulled the distributor and swapped out the pickup, and the engine fired right up.

Maybe I missed it, but I didn't see you mention anything about the CEL or pulling codes. Those are the only ways that the computer has to communicate back, and since it's in charge of the whole operation, ignoring what all it has to say needlessly ignores important clues to the problem.

 

I checked the codes before and didn't find anything related. I will do it again tomorrow when I check PIP. Thanks!

 

I just checked KOEO code and I got:

633 (4x4 switch is closed);
622 (shift solenoid #2 circuit fault);
111 (I don't know what it is).

I also did KOEO wiggle test and it says "circuit fault detected" and didn't say what circuit.

So now I guess I still don't know if the PCM is broken or not. I will check some wiring, especially around the distributor next.

 

A few comments:
- If not using a code reader: It's VERY common to mess up manually reading the codes - plenty of posts can be found on here where someone first reports a set of codes that don't make any sense, then revises their methodology and reports a different set. If there's any doubt, invest in an OBD1 code reader. Autozone has the Innova 3145 for $27, and it comes with a useful book.
- What I'd expect is something like:
a) KOEO codes - either '111' if all is clear, or, a set of fault codes; followed by ...
b) The Separation Code, '10', indicating that the KOEO codes are done and the Continuous Memory codes are about to start; followed by ...
c) Continuous Memory codes - either '111' if all is clear, or a set of fault codes.
- Assuming that you saw this order: '633', '622', '10', '111', then that's probably a correct reading. If so, it's probably worth investing at least a little time into finding out why 633 & 622 are being generated and fixing whatever is causing them.
- For the wiggle test, you can either confine testing to only a single element ( a wire, a connector, or a sensor) or only to a specific group of elements. If something in a group fails, then divide that into sections and wiggle-test each section independently. For groups that pass, you're done with them; sub-divide groups that fail and iterate until you've zeroed-in on the problem(s).
- In case some Continuous Memory codes were somehow inadvertently cleared, it might be worth trying to start the engine a few times and then immediately checking the CM codes again.
- It sounds like you checked for signal at the injectors themselves; maybe verify that the signal is also not at the PCM-end of the wiring too (or at least as close to the PCM as you can reasonably get).

 

There is a thread titled “ PCM thinks transfercase is in low range” from Dec 2025 that has testing for those codes. Was the transfer case is in 4wd low when you performed the test? As already mentioned, code 111 is system pass. Was that displayed at the end for the memory codes?

 

I use a Craftsman 20899 that shows the codes directly on the screen. I checked signals at multiple injectors so shouldn't be wiring.

 

Since you measured battery voltage on both sides of the injectors, it could very well still be a wiring issue. The fuel injectors are effectively just solenoids, and if they are good but not getting a ground, the supply voltage will look pretty much identical to the voltage on the switched side. So if they are open circuit to the PCM and you measure voltage on both sides of them with them still in circuit, such as back-probing them, you will see battery voltage on both sides.

When you tested for signal were you back-probing the connector or did you unplug the injectors and probe the connector directly?

-Rod

 

I'm assuming that this is a 5.8, since that's the only 94 in your sig, and will further assume that it's Fed emissions, in which case it's very probably got batch-fired injectors: one output from the PCM fires four injectors simultaneously, and another fires the other four. Depending on which injectors you checked, it's plausible that they were all in the same batch and you only looked at the injector-end of a single signal, and it could further be that there's an open between the PCM and these injectors before it branches off or in a connector. Even if by chance you looked at both of the injector signals, those both pass through at least two connectors and problems there could also be the cause.
While at the PCM-end of the PCM's harness, that would be a good time to make sure PIP is getting there.

In my mind, there are two issues to track down at this point, in this priority:
A) Something failed the wiggle test - maybe more than one thing. Maybe this is some signal that the PCM needs before it will fire an injector (like PIP - without that, it might not even know that you're trying to start it, which could explain the missing CM codes in a non-running engine); in any case, disconnecting any signal from the PCM isn't good. I'd want to fully resolve that first, see if it will run, and dump codes again.
B) Is the PCM outputting grounds to the injectors - yes/no - and if not then why not? The most straight-forward test is to look at the two injector signals as close to the output of the PCM as you can manage; a breakout box would be ideal, but probably not available. Note that the PCM is just pulling these outputs to ground when a bank is supposed to fire, otherwise leaving the output open (floating) so the only way you'd see a voltage pulse here is if the output is tied to some sort of pull-up load w/12V at the other end (like an injector or even a large resistor; so, expect to have to fake a load).
If there are no signals here, then this splits into:
a) Is this a good PCM that is lacking some necessary input before it will fire injectors?, or
b) is the PCM bad?
A few ways to resolve that are:
- Follow the troubleshooting procedure in the Powertrain/Emissions Troubleshooting manual (this would be my Plan A),
- Swap in a known-good PCM (though, to some degree, this risks damaging it; PCMs are getting expensive; if you plan to keep this truck, it's worth scrounging up a spare),
- Fix whatever is causing the two fault codes; just because it doesn't seem like they would prevent starting doesn't mean that they aren't,
- Get a schematic of the engine-to-PCM wiring (like in the EVTM) and methodically check signals and wire continuity end-to-end; like go through all of the sensors one at a time, then go through all of the actuators

 

I would verify the rotor turns in the distributor, seeing as it was replaced (sheared roll pin is common on dual drilled gears on reman distributors)
No talk of checking for a blinking light on the negative side of the coil when trying to start it?
That is the PIP test and yes, the PIP signal generates the pulse signal for the injectors in the PCM too
Code 111 is a system pass code, after a separator code 10
For your 1994, 111-10-111 is a complete system pass
First set of numbers are continuous codes (problem right now codes) followed by the separator code and the second set are memory codes KAM codes

 

Could be as simple as TPS is bad, and if ECM thinks it is held at wide open throttle, that stops the injectors from firing.
how to test it-->Throttle Position Sensor Testing, Replacement and Adjustment | Full Size Ford Bronco Forum

 

Thank you very much for the detailed suggestions. Sorry I got distracted these days.

If PCM fires four injectors simultaneously (I assume one bank), then if one bank injectors can fire, the car can still run rough a little bit, right? So this means if it's wiring problem, then at least two wires have to fail at the same time. This makes this scenario remote, right?

I just checked the distributor. It has 7 wired coming out from the bottom to a connector. This connector then connect to 5 wires to the receiving connector. They all connect good. Now these 5 wires may go to the PCM, but it's hard to trace them. I can only check the connector ends to make sure no broken wires in those most vulnerable areas. Wires break somewhere in the middle is very rare, especially there is nothing there to touch them.

I now disconnected the PCM. Is there anyway to quickly check all the signal lines to make sure the PCM gets what it needs to fire the injectors?

Preparing a backup PCM is a good idea. I will start looking.

Thanks again!

 

Since I can use starting fluid to keep the car running, the distributor should work just fine, right? Thanks!

 

A good hint. I will check it next. Thanks!

 

Did you look through and perform the tests from this thread with the same codes that you have or did you ignore what I found and posted?

 

On a 30+ year old vehicle with an unknown history, nothing can be assumed. And in general, assumptions are your worst enemy when troubleshooting (bad logic is probably number 2). Ford itself had a lot of trouble with wiring and connectors when transitioning to EFI. Now we've got decades of field use and abuse on top of what they ultimately decided was the cheapest connectivity they could get away with at the time. And it's impossible to know what all some PO thought was a good idea, but really wasn't at all. That being said, Ford's OEM wiring and connectors for this generation of EFI/SFI are actually pretty good (though at 30 years the plastic vacuum lines are absolutely not).

Depending on exactly what was measured, all that it sounds like can be stated as a 'fact' at this point is that the energizing signal to some of the injectors wasn't there when it should have been. Continuity from any injector to the PCM is an unknown - which includes passing through at least two connectors that might not even be plugged together as far as we know. We know nothing about the wiring, which at some unobserved spot could be a tangle of oxidation balled up in mud-covered electrical tape. Signal output right at the PCM is also completely unknown.

If there's no signal at an injector, the two necessary measurements are: is there continuity between this injector and the PCM, and, is there an output signal at the PCM?


At a bare minimum, you need a copy of the 1994 Bronco EVTM. It will have a schematic for your engine harness, a location map of each connector, the pinout of the PCM, and a lot of other stuff that will be useful as you deal with other eventual problems.
If you want to learn how your whole EFI system is working and how to test the individual sensors and actuators, "Ford Fuel Injection & Electronic Engine Control" Vol. 2 by Charles Probst will be invaluable. The schematic in there for the 92-93 Bronco 5.8l engine harness is probably identical to your 94's (and is a lot more readable than that in the EVTM, but doesn't include fine details like the connectors).


From the PCM connector, you should be able to test continuity from the PCM to the injectors, and since the ignition system runs largely stand-alone, observe that PIP shows up at the PCM connector when cranking (and that wiggling doesn't affect any of them).


Again, the failed wiggle test is a major smoking gun. Without that resolved, every measurement you take will be suspect.