High RPM on highway, not shifting into OD?
 

I recently bought a 1994 Ranger with a 4.0 and auto transmission. I'm having some engine bogging/misfiring issues, so I'm not sure if these issues are related or not. When I'm driving on the highway it sounds like the engine is really winding up just cruising at 55-60 MPH. I don't have a tachometer so I can't tell what RPM it's actually at. Could it be a really low geared rear axle (4:10)?
It also seems to only shift from 1st to 2nd, and 2nd to 3rd. I can't tell that it drops down into overdrive at all. Again, I'm not sure if that's because the engine is acting up or not.

The truck has approx. 132,000 miles and I doubt the transmission fluid has ever been changed. It is on my list of things to do when I get a day off from work.

Any and all ideas would be appreciated. Thank you.

1994 Ranger will have A4LD automatic transmission, this was Fords first computer assisted transmission, it has two solenoids in the transmission.

TCC solenoid, which locked up torque converter when cruising giving better MPG and performance.

3/4 shift solenoid, which shifted transmission into 4th gear(OD) when engine RPMs and speedometer were at or above preset parameters.
This 3/4 solenoid was also Driver controlled.
There will be an OD button in the cab, usually on shifter, and an OD light in the dash to show status of OD, ON/OFF, OD button OFF prevents shifting into 4th(OD), you would use this when climbing longer uphill grades or when pulling a trailer, so you didn't get constant 3/4 shifting


Flashing OD light indicates a problem with wiring or solenoid.
Both solenoids share one 12volt wire, this wire will have 12volts when key is turned on, the 12volts passes thru each solenoid and to the computer, each solenoid has it's own wire to computer, this is the 3 wire connector you see on the side of the transmission.

Since a solenoid is just a coil of wire the computer will "see" 12 volts on each wire when key is on, indicating that the solenoid wiring is OK.

Flashing OD light means general transmission problem, not necessarily an OD problem, it acts as a warning light, like Check Engine light(CEL), but for transmission.

Your OD light may be burned out or......................someone removed it because it was flashing, hard to sell a vehicle with flashing dash board light.
Not saying that is what happened, just saying it has happened before, also sellers remove Check Engine light bub or black it out for the same reason.

Just FYI, CEL should come on when you turn on the key, then go off after startup, if this doesn't happen then CEL bulb may also be "burned out"

You can test both solenoids with an OHM meter at the connector on the side of the trans, you can also check for 12volts with Key ON at that same connector

My gear selector has a position for overdrive, not a button. It goes Park, Reverse, Neutral, Overdrive, Drive, 2nd, 1st.

I can hear it shift from 1st to 2nd, and from 2nd to 3rd, but then it just keeps winding up. It acts like the gear shift is in drive (3rd), even though I have it in overdrive.

Then there has to be a switch that tells computer to use 3/4 shift solenoid when shifter is in OD position and not use it when in Drive, otherwise why have the two positions

Just above the shift linkage on the side of the transmission is the NSS(neutral safety switch)
It is a plunger type switch that screws in to trans, a Cam inside the trans that is attached to the shifter rod pushes the plunger up and down to make and break connections in the NSS depending on what gear is selected.
I.E. starter motor activation wire passes thru this switch, this prevents starter motor from working unless trans is in Park or Neutral.
It is popular to By-Pass this switch if truck won't start, this could disable OD in your model since it doesn't use a separate button.

Worth a look to see if wiring there has been modified.

Image of NSS switch here: http://i.ebayimg.com/05/!BgbGB1wCGk~$(KGrHqIH-DoEsK+HSKe)BLFRZzK5jg~~_35.JPG?set_id=8800005007

This is a 4 pin NSS and 2 of those pins are for reverse light, other 2 are for starter motor activation, so Neutral detection, yours may have 5 pins for OD detection, not sure
I assume the Reverse(backup) lights work

Or the 3/4 shift solenoid may have failed, check OHMs to see, it is just a coiled wire so should be 5-8ohms

Ok, thanks! I will look into that.

So I hooked the truck up to the code reader because of my engine issues, and two transmission related codes came up. I don't remember the actual code numbers, but one was a code for the 3-4 shift solenoid failure, and the other was a converter clutch switch/solenoid failure.

How easy are these to repair?

Code numbers are very important, "I don't remember the actual code numbers" is worse than not having read them at all.


You need to check the OHMs for the TCC and 3/4 shift solenoids.
Remove connector on the side of the transmission and test them.
If they test OK then problem is in the wiring to the computer or lack of 12volts at the transmission

Ok, I found the codes. Hopefully this helps.

629 - converter clutch solenoid circuit fault

566 - 3-4 shift solenoid circuit fault

Both happening at the same times means wiring or 12volt power at transmission is most likely problem.

To have two separate solenoids fail at the same time would be very high odds against.

Unless transmissions was abused, overheated and/or run low on fluid.

"circuit fault" means wires are disconnected
Each solenoid gets 12volts when key is on, if computer doesn't "see" the 12volts on it's solenoid wire for that solenoid it sets the "circuit fault" code for that solenoid

A solenoid is just 1 wire coiled around a metal tube, solenoid failure is when that 1 wire breaks somewhere in the winding or the connection

12volts-----------------solenoid------------------computer

Thanks. I will look into those