Hello! I've been using this forum a LOT over the past few weeks trying to get my 93 Ranger 4.0 4x4 Extended Cab running again. This might end up a TLDR post, but I'm hoping by providing as much detail as I can on what I've done and tested will lead to someone having a lot more knowledge than I putting their finger on what I finally need to do to get the "Red Ranger" back in service.

Background: A number of months ago, the Red Ranger decided to not start one day after running fine the day previous. After a couple attempts and it cranking longer than usual, it started. I moved it in the driveway and left it running, walked inside the house, came out and it had died, and it wouldn't start again.

After trial and error I realized that if I turned the key to accessory position I would no longer hear the fuel pump "prime." But if I turned the key back and forth enough times, eventually I would hear the fuel pump. When I would hear the fuel pump prime, I knew the truck would start, and it did. Eventually,
I couldn't play with the key back and forth enough to hear the fuel pump, so now it will not start at all. It will crank fine, but will not start.

So, I've got another "crank but won't start" problem. Let me tell you what I've diagnosed at this point starting with were I am today and going backward. Let me start by saying I am NOT a mechanic, but I really would like to conquer this problem with the Red Ranger.

I've gotten to the point where I THINK the PCM is bad and not getting power. I need to determine if the PCM is bad and in need of replacement. I don't want to throw much more money at it without knowing with certainty that it needs to be replaced. Not to mention, I don't want to go through the trouble of removing the darn thing if I don't have to. Although, I get the feeling I'm going to need to remove it though to test it since it's so hard to get to.

I do not think the PCM is getting power. When I turn the key to accessory, the CEL does not come on. I do NOT know however if the bulb is out. I don't remember if I had seen the CEL light come on prior to the truck acting up.

• When I ground the Fuel Pump test slot in the OBD1 connector, I turn the key, hear the relay click and can hear the fuel pump. At this point I have fuel at the Schroeder valve on top of the engine.
• I have about 11.6-11.8 v at the fuel pump when I ground this OBD1 slot
• I have spark.
• The truck will start with enough starter fluid pumped into the air intake
• I've unplugged the TPS to see if it would start that way after reading it could be a bad TPS and it should start if unplugged. No dice.
• I found somewhere that I could check the power at the TPS by checking voltage on 2 of the wires to give indication that the PCM was getting power. I don't remember exactly which two wires they were but I have no voltage with the key on at the TPS.
• I've replace the fuel pump relay, the crankshaft position sensor, the ignition coil, and even replaced the fuel pump.

So the questions...

• Should I pull the PCM to get more accessibility to it to test it further? Is there an easier way to check to see if the PCM is good/bad? I do not know where to look for grounds to the PCM.
• Or do I have enough evidence to be confident on spending money on a new PCM?
• Any comments on the easiest/quickest way to get that bugger out of there?
• Should I be looking somewhere else entirely to diagnose this issue?
• Could it have something to do with the ignition switch? How would I troubleshoot this?

Follow up questions would be, what precise other testing would I do once I got the PCM out of the vehicle? If I do replace the PCM, is it a simple swap or do I need to do something to get the truck to work with the new computer?

Thanks so much for reading! I'd like to get this little truck running. Aside from this issue it's been a great vehicle and I want to get it running for a new 16 year old driver in the family. Not to mention I'd like to get it out of MY stall in the garage! :)

Regards,
Infman

 

Welcome to the forum

Or welcome on your first post in the forum

The under 12volts on volt test is troubling
Battery voltage should be between 12.3v and 12.8v
Under 12.3v is a failing battery, try charging it, but if after sitting over night(not charging), its under 12.3v again replace it
This can cause issues because when starter motor is activated, system voltage will drop up to 2.5 volts, staying above 10volts is important to keep electronics powered up
So low battery volts can cause PCM to reset during cranking, so start and no start

There is no way to test a PCM
You can test the wires that go to the PCM

No CEL is an issue, the CEL bulb gets 12volts with key on, the PCM pin 17 GROUNDS that bulb when computer is powered and booting up
This Ground is also on the OBD1 connector, seen here: https://www.therangerstation.com/tec...ry/OBD_I.shtml

The Self test OUT is the CEL ground from computer pin 17, so hook test light/meter to battery positive and to this slot in OBD1 connector
Key on should see light or 12volts on meter
It means PCM is powering up
If no light/12v then computer is not powering up

Here are the wiring diagrams for 1994 4.0l which will be the same for 1993, but fuse numbers can be different year to year

PCM failure is rare, but can happen
There are 3 blue capacitors that can leak and fail after 20+ years, seen here: Ford EEC-IV

If you do pull out the PCM, pop the top and have a look, these can be replaced(under $5) and the board cleaned up, it this is the issue

 

Ron,

Thanks for your reply!!

I've read a lot of your posts here attempting to diagnose this problem. Your insight, as well as others here, has been very helpful!

Connected to battery positive, there's no light on my tester on Self Test OUT. Meter reads 0.02v

I did put a battery charger on my battery, although I haven't charged it at all since I've started diagnosing quite some time ago and it's still cranking away
I tested with the 12 v charging on and get the same results on the Self Test OUT.

Where do you think I should go from here?

Thanks again!
Infman

 

Thats KEY ON, and no Ground at Self Test OUT, right?


Then a couple of other tests
KEY ON
Test for 12volts at the coil pack, the Red wire, this comes from the ignition switch
If no 12v then ignition switch under steering column is suspect

If there is 12v on coil wire, then test Red wire on MAF sensor, MAF has 4 wires, red one should have 12v key on from PCM Relay and PCM fuse

 

Correct, KEY ON, no ground at Self Test OUT.

Interesting... the test for 12v at coil pack red wire is 0v. This red wire, correct?




Pardon my ignorance, but wouldn't that not allow the truck to spark when cranking?

Anyway, I also suspected possibly the ignition switch, and had part of the steering column and dash under the column apart already, but I was struggling to find anything I could test or trace.

Thanks again!!
Infman

 

Yes, unplug the 4 wire connector, the red wire should show 12v key on

It reads like your problem was intermittent, so yes no 12v there would be no spark and NO fuel pump either, as this 12v also activated the PCM relay, which activates the PCM and then fuel pump relay

 

KEY ON I have 0v at that red wire. However my spark tester in line with a spark plug is showing spark on cranking the engine.

 

Well that can't happen, so not sure what to tell you

All 3 coils in the coil pack share that one 12v wire so...............

There are TWO power paths in the ignition switch, one for RUN(on) and one for Crank(START) so it is possible the RUN connection is bad but the START is working, so you have 12v(spark) in START but no 12v in RUN(key on)

Anyway, that red/light green stripe wire runs all the way back to the ignition switch under the steering column, so the ignition switch may be the culprit for no power
You can pull ignition switch down and reconnect it and manually slide into its 4 positions for testing

There is a 60amp fuse in engine fuse box, it feeds power to ignition switch on the 2 yellow wires seen on the switch

 

Good morning!

I must be dumb. I am struggling mightily to find the red/lt green and yellow wires under the steering column.

I thought I had found them, but I only have the wires plugging into the turn signal assembly. I've been looking for some sort of picture or video all over the internet for the actual location of where I can put a tester probe into a plug or something under the column and I can't for the life of me find them.

I have a feeling they might reach out and slap me if they could, but I'd be completely blind sided because I can't find them.

 

OK, so I found a way to test that red/lt green wire from the ignition and found that I must have incorrectly tested (or didn't have a good connection with my meter at the coil) the reading at the coil.

I found the red/lt green wire in the connector under the power distribution box behind the battery, as indicated by the picture. The blue arrow tip is right on the wire. This is the side of the connector coming from the firewall.



KEY ON, multimeter shows 11.9v.

Then I tested continuity from the other side of the connector to the ignition coil plug. Continuity test went to zero on my meter. This made me make a funny face, as if all this is correct, I should have had 12 v at the ignition plug yesterday.

I plugged the connector back in under the power distribution box and did a KEY ON test to the ignition coil and this time have 11.9 v just as I had at the connector under the Power distribution box.

So things are just a bit different in my troubleshooting. I'm going to check the MAF sensor next.

 

I have now tested the MAF and have 12 v on the red wire KEY ON.

I'm hoping there's another step now that we've determined these items :)
Oh, and my apologies for the inaccurate reading on the red/lt grn coil wire. I also retested KEY ON battery positive to Self Test OUT, but still have a reading of 0.02v

Thanks again!!
Infman

 

Not sure what you are testing under the dash?

The ignition switch is bolted to the steering column(under the dash) and its wiring connector is 10-15 wires

The wires coming down out of the steering column are not for the engine
The key cylinder has no wiring, well just the "dinger" wire if you leave keys in ignition with door open
When you turn the key it slides a rod(actuator) inside the column that slides the ignition switch into its 4 positions, ACC OFF RUN START


But if you have 12v on MAFs red wire with key ON that means the EEC relay is closing so EEC/PCM should be booting up, and CEL should be on
You can test if your CEL bulb works by Grounding the Self test OUT then turn on the key, CEL should light up, thats just a bulb test, and thats what the PCM should be doing when it boots up

But still no 12v at the Coil with key on?

 

I was misunderstanding your comments about "pulling the ignition switch down". That's what had me under the dash... Pardon my ignorance.

I grounded Self Test OUT and when I turn the key to ACC the check engine light comes ON.

As I stated a post or two ago, I must have messed up my testing at the ignition coil. Upon retesting, I DO have 12 v at the ignition coil.

• 12 v at ignition coil KEY ON
• 12 v at MAF sensor KEY ON
• CEL ON when Self Test OUT is grounded KEY ON
• Still no CEL by just turning key to ACC
• Still no fuel pump prime turning key to ACC

 

ACC doesn't activate engine systems, like computer, coil, fuel pump or MAF, its just for radio and interior lights
So thats normal

Key in RUN(on) activates those system
So no CEL key on means computer is not getting 12v or is dead

 

OK, so my ignorance again.. when I said ACC I meant RUN. Key turned forward, not backward.

So then am I to the point of confirming the PCM (computer) needs replacement?
At this point do I go through the process of getting the PCM pulled out and opened to see if there are any capacitors that look damaged?

Just looking for insight as to my next step.

Thanks very much for your assistance through this.

 

Yes, get computer out and test the RED wires at pins 37 and 57 to makes sure they have 12v with key on, these power up the computer

Pin numbering seen here: http://www.auto-diagnostics.info/ford_eec_iv

You can use a sewing pin/needle to pierce a wire to test voltage or ground, if needed

And if there is 12v on both then open it up and have a look inside, warranty is over, lol

 

Whelp.... I do not have 12 v on either 37 or 57 if I'm testing them correctly KEY ON.... This is connected to 57. I get the same in pin 37

Where do I possibly look for the other end of these wires? I'm assuming they are in the power distribution box somewhere?

 

Pin 40 (Ground) to positive battery terminal is 12.4 v. So the ground is good there, correct?

According to the wiring diagram, pins 37 and 57 should to back to the ECC relay in the power distribution box on "blade" 87 of the relay... I think...

Not sure if I'm deducing that correctly.. but if that is correct, I don't have continuity from either pin 37 or 57 to that point under the relay.

Maybe I'm misreading something.

 

I've further determined that "blade" 87 under the ECC relay does indeed go to 12 v KEY ON.

The way I read the wiring diagram, that then feeds pin 37 and 57. Where would that one red wire split to two then?
Also, according to the wiring diagram, this red wire feeds the MAF and the ignition coil, both have 12 volts.

I'm thinking this has to be between this point and the computer connector. I'm not sure where to look for the convergence of these wires.

 

Good work, good testing

Yes there is a splice in the harness that powers many devices when EEC relay closes, that red wire runs everywhere, lol
If you can find the two red wires in the EEC's harness, you can test them to be sure its not the EEC connector, then cut and splice them to MAF's red wire, quick fix

I do not know where to find that RED WIRE splice in the engine bay but it would be good to locate it if its corroding, because fuel injectors also all share that red wire

MAFs red wire will run to that splice as will fuel injectors red wire

 

Thanks, Ron

It will take me a while to get to searching for that. Planting season has started and long days equals not a lot of time to troubleshoot unless we get some rain...

I will post back when I find it tho.

Thanks again!!

 

Sounds good

At least it looks like a "cheap" fix, if its just a bad splice

 

Happy Easter!

Started looking for a splice today. Got quite a bit of the wrap off the wires and found the red wires leading to the connector to the computer for power on pins 37 and 57. This led me to discover that the pinout diagram that was linked in post #16 is inaccurate. The way that the diagram for the pinout reads is actually opposite in my case. Using that pinout, my red wire for pin 37 would be in pin 24 on the diagram and 57 would be pin 44 in the diagram. It appears the numbers may be reversed.

So I went back to testing and found that I do INDEED have 12 v on the red power wires in the PCM connector.

Therefore I opened the computer cover and took a look. I immediately noticed a blown capacitor on the board.




I've since de-soldered the capacitor and have ordered a cap kit that includes the type I need. I've got the board cleaned up a bit and I'm hoping that soldering that cap back in place will be the fix I need!

 

Yes, 25 year old Caps will cause issues

Not sure if maybe you are reading the pin numbers in reverse order?
Find the Yellow wire on Pin 1

I have these for the 1993/4 4.0l
pin 37 and 57 are the key on 12v for PCM

 

It's running!

Ended up buying a new ECM for the truck. Replacing capacitors didn't do the trick. Found a reasonable ECM, swapped it out, and the truck started first go.

Just to clarify on the pinout difference mentioned a couple posts ago.. I've added an image of what the pinout from the website was documented as, and what my actual pinout was. It was reversed. The yellow wire on pin one was on the opposite end of what the diagram shows, and my red (pin 37 and 57) are on the opposite end as opposed to where the diagram shows.



Bottom line, it's running.

Ron, your advice has been fantastic. I appreciate your expertise and willingness to help.

Hopefully information in this thread can help someone else with their particular problem if that need ever arises.

I have a 16 yr old boy that is very happy!! :)

Thanks again.