So I’m at quite the loss right now. I bought this ‘93 4.0 (automatic) months ago. Had its fair share of issues and leaked almost every fluid. I’ve been working on it for quite a while. After doing quite a lot of work in the garage I took it out for a test drive a few months ago and it would not shift out of first. After hitting a certain speed, the RPMs would drop to basically an idle while moving. If I was to hit the gas it would react oddly by revving and then dropping repeatedly.

As far as I was aware, the transmission was shot so I thought that would be the issue. Well after pulling it out, having it rebuilt, and then putting it back in, the issue is still present.

I don’t regret getting the rebuild as the fluid was darker than used engine oil and the pan and lines were full of metal. The issue I originally had is still present and I now believe it is electrical with the way the engine simply cuts off instead of switching gears. According to the electrical manual, there is quite a few components that communicate with each other in order to determine shift scheduling along with the torque converter clutch operation.

I feel that a few of the culprits could the Throttle Position Sensor or the Vehicle Speed Sensor. Any guidance on the issue is greatly appreciated.

 

You have an A4LD automatic in a 1993 Ranger
It only has 2 solenoids and only one that does shifting, it is the 3-4 shift solenoid for overdrive only, shifting into 4th gear from 3rd

2nd and 3rd shifts are controlled by a governor and Vacuum Modulator, I am betting the vacuum modulator is unplugged from the engine
Modulator is on the passenger side of transmission, it has a vacuum hose that runs up to the intake manifold, it detects engine LOAD for shifting into 2nd or 3rd gear

TPS is easy enough to test with a Volt meter and a sewing needle
It has 3 wires
5volts, from computer
Return, volts to computer
Ground

That's the usual orientation
You can ground the volt meter to battery negative or any engine ground
Use a sewing needle to pierce the center wire's insulation, pushing it in at an angle its easier
Key on engine off
Throttle closed you should see 0.69v to 0.99v, under 1volt
Manually open the throttle and voltage should start to go up
At WOT(wide open throttle) you should see 4.5v-4.6v
Move throttle slowly open and closed, there should be NO voltage drop or spikes, if so replace it
TPS is the same as a volume control or light dimmer, a variable resistor, so nice smooth voltage increases and decreases, you can also use an OHM meter to test it, key off unplugged

Assuming speedometer works OK
VSS is only used by computer and cruise control(if so equipped), speedometer uses a cable in 1993
On the drivers side of transmission's tail shaft(2WD) you will see this sticking out: https://www.therangerstation.com/tec...peedsensor.gif
It has the speedometer cable hook up and the VSS
You can test the VSS part with an OHM meter, it has 2 wires, contacts
Unplug the 2 wire connector
Use OHM meter to test the 2 pins in the VSS, should see 190-250 OHMs

The VSS signal to computer is only used to lock torque converter(TCC solenoid) and for shifting into OD(3-4 shift solenoid)
Nothing to do with shifting out of 1st to 2nd and then to 3rd gear with an A4LD

 

I ended up checking the TPS shortly after I made this post, mostly because I was messing with it long before I did the transmission work and lo and behold I was getting close to zero Volts out of the sensor. Upon relacing the TPS I could finally shift properly out of first. That is a complete different story in itself but the voltage is completely out of range as it was with the original one.

Funny enough the owner before must've had his own idle issues so he decided to drill a hole in the throttle plate which was then plugged with a screw. The original voltage I read without adjusting anything was right around 1.45V. Out of curiosity, I wanted to see how low I could get the voltage without the truck running (it would die long before I got there). The anti diesel screw was completely out and the voltage still read 1.18V. I'm aware people have bored out the screw holes on the sensor but I don't want to jump to that considering they're metal screw holes and I spent $50 on the part.

Since the engine idles really bad the more the throttle plate is closed, I instead took the screw out of the drilled hole on the throttle plate to allow more air flow and was able to get the voltage down to around 1.27V comfortably with the engine RPMs at right around 700 consistently. I'm assuming I have some communication issues between sensors or the IAC isn't working properly. The engine is running rich enough to burn your eyes and I'm sure the voltage has a factor in that. The O2 sensors have been replaced so I know that is not a factor. I also don't think there is any issues within the transmission or its solenoids because the shop that rebuilt my A4LD is very reputable.

Now that I've driven it more, I found that it shifts alright for a rebuilt transmission, but the RPMs will consistently drop down to idle the moment you take your foot off the gas. Most of the time it is not a slow decent from whatever it was revved to but an irregularly fast decline to an idle and then it seems to climb back up some. To answer your question about the speedo, it does not work properly, mostly because of the incorrect tire size that the previous owner chose. Even then the speedometer doesn't seem to be consistently climbing like it should be, oversized tires or not. I will carry out the VSS testing tomorrow so thank you for that info. Besides all of this, the truck is running on a 2.3L California Emissions ECU so as soon as I have the money and it is available on Rock Auto I plan on buying a proper one.

As always, thanks for your help Ron.