1994 3.0 2WD Manual vs Auto PCM wiring?

ter240 · May 23, 2018

So I did a swap from the auto to a manual. During the swap I installed a manual PCM. I did not change the engine harness because my research suggested that it wasn't necessary (basically the new PCM isn't looking for the auto).

Since the swap I've been getting lots of codes and drive ability issues. Finally took it to my mechanic and he thinks it has to do with the PCM and harness not being compatable.

From the diagrams I can find, which aren't always consistent, there are only two pins on the PCM that deal with the auto, 52 for the 3-4 shift solenoid, and 53 for the torque lock-up.

Anybody have a good, as in Ford wiring diagram?
Any suggestions? Some that come to mind are 1) remove these two pins form the PCM harness, or 2) connect the auto solenoids to the harness. Really rather not have to swap the engine harness.

Thanks

BlackBII · May 23, 2018

ter240 said:
Since the swap I've been getting lots of codes and drive ability issues.

Which codes and what drive ability issues?

I would start by pulling those pins to see if anything changes.

Here's what I have:

Denisefwd93 · May 23, 2018

I've had as many people tell me not to change the PCM as of I've had people tell me to change the PCM on the mid and early 90s Rangers because the a4ld, automatic really didn't go through the PCM but what do I know, I just did the obvious and got a different truck that already has manual shift, wanna to buy my truck with auto ? lol

RonD · May 23, 2018

You added a clutch pedal and above the clutch pedal there would have been a connector for the Clutch Pedal switch, with an automatic this connector is plugged into the AUTOMATIC Neutral Safety switch harness, so you would unplug the AUTO connetion and plug the connector into your Clutch switch on the clutch pedal push rod

Drawing of that setup here: https://www.2carpros.com/images/question_images/182597/original.jpg

The clutch switch connector is on ALL Rangers, Ford just adds an extension wiring harness to it when the Ranger gets Automatic trans.

This switch tells the computer when clutch pedal is up or down, and this sets idle RPMs and REV Limiter, so it is needed.
It also prevents starter motor from working in clutch pedal is not pushed down, so I assume you did some wiring changes on the automatic harness so you could start the engine.

Picture here of the connector plugged into the switch: https://www.2carpros.com/images/question_images/11347/large.JPG

The pin 52 or 53 may be used for EGR system if that computer came from an EGR equipped vehicle, so if you are getting EGR codes then thats the problem

And yes, describe driving issues and list codes
1994 computer will use 3 digit codes

ter240 · May 23, 2018

Thanks for the suggestions and the diagram. It is the same one I found for the auto harness.

The rest of the pedal wiring and start relay connections are in place and working properly.

The codes are numerous and we're getting abnormal reading on most of the sensors. At this point I'm down to chasing either a bad PCM or repinning the harness if i can figure out any differences between the two harness pinouts.

Anybody know if the manual pinout is different from the one shared above?

Denisefwd93 · May 23, 2018

After check all your grounds, check all your grounds

What are the codes???

Numerous, doesn't help those trying to help, jus sayin

ter240 · May 24, 2018

I checked the vacuum lines and the grounds, also had a professional mechanic re-look at everything.

That's why I came to the conclusion, and asked the question about the harness pinout differences between the auto and the manual. Anybody?

Denisefwd93 · May 24, 2018

Put the original PCM back

RonD · May 24, 2018

No, the "pin outs"(wiring) are standard for Ford EEC-IV computers, the differences are the firmware/software loaded onto the computer when it was made/installed in to the vehicle.
The EGR and Automatic wires will be connected at the computer even if a vehicle has no EGR system or came with manual trans, main wiring harness is designed for all options.
My 1994 is factory manual trans but has automatic 3 wire connector at the firewall behind engine, just has a plastic cover over it since it was not used

A manual trans computer won't have the Check or Circuit that operates an automatic trans solenoids.

And yes, you can use your automatic trans computer, it will just turn on the CEL because solenoids are not connected and don't respond when grounded, but thats the ONLY codes you would get if everything else is OK.

So as Denisefwd93 suggested, put in original PCM and then check codes after full warm up and driving.

ter240 · May 24, 2018

Thanks. I will give that a try.

The reason I used the manual PCM was to avoid the CEL issue and the other codes. Also understand that the auto computer would limit RPM?

Really thinking that your first point is the root cause, new software loaded during the refurb process at Cardone.

pjtoledo · May 24, 2018

ter240 said:
Thanks. I will give that a try.

The reason I used the manual PCM was to avoid the CEL issue and the other codes. Also understand that the auto computer would limit RPM?

Really thinking that your first point is the root cause, new software loaded during the refurb process at Cardone.

auto computers limit RPMs in park and neutral to prevent damage to the converter. not sure how that will affect your setup.

ter240 · May 26, 2018

Problems Solved!

Ordered a replacement PCM from RockAuto on a warranty claim because the one I was running, and having problems with, was only a month old. Installed it and the truck runs great. No idle, acceleration, stumbling or weird rev issues. Also no CEL lights.

When I had the two supposedly same PCM's from RockAuto side by side I did notice that the cases were slightly different and the OEM tag was missing from the first one. They both had the same reman part number (785796). Guess I'll chalk this one up to incompatible software or hardware.

Thanks for the suggestions.

adsm08 · May 26, 2018

pjtoledo said:
auto computers limit RPMs in park and neutral to prevent damage to the converter. not sure how that will affect your setup.

Using an auto computer with the manual trans means the computer never sees the trans shift out of P/N position, and so the rev limiter is always engaged.

RonD · May 26, 2018

Good work

Thanks for posting the update and the FIX

BeardedVeteran · Jun 21, 2018

1994 Ranger 3.0 XLt lb standard cab

not sure how or where to post my own thread on a forum. need some help though.

these 2 connectors are coming from the main wiring harness on the alternator. they are hanging down nearby the starter and firewall on the driver side. i checked by the power distribution box, the battery and fender. i have no clue where these go. my alternator definitely is not operating and this is the culprit. i recently replaced the water pump.

Pictures are here

https://www.cargurus.com/Cars/Discussion-t1099_ds913190

1994 3.0 2WD Manual vs Auto PCM wiring?

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