Actually we don't know that.

 

Don't know what?

 

The speed control module?

 

We don't know what any pressure is anytime . Hunches tell nothing. Figures and facts do. Can you tell me what the line pressure is with 452 set? Be nice to know.

 

He has hard shifts so we know the pressure is higher than normal.

 

Yes the speed control module has been known to cause this also as it can cause the signal from the PSOM to the PCM to be bad.
Just unplug it for a test.

 

Pull the RABS Flashout Codes

 

What and where is the speed control module? I am not familiar with that. Also I tried to pull the RABS codes before and none came up, and I have plenty of fluid.

 

A photo from Subford:


Speed Control is Ford's version of Cruise Control which is a GM term.




If the yellow Brake lamp is also on you will not be able to pull the RABS codes. If the yellow Brake lamp is not and you are unable to pull the RABS flashout codes you may have the older RABS-I system which does not have the Keep Alive Memory (KAM) function. You have to keep the key in the On position. Or if you have RABS-II, the controller may be bad.

I believe your 1992 MY trucks uses the older RABS-I system.

 

The cruise control? Mine looks like this and has a 6 wire plug that is showing. (The cruise does not work btw never did)

 

It is located under the dash near the column behind lower center of I/P.
If it does not work unplug it anyway.
It is called a Amplifier in the diagram below.





/

 

I caught the RABS-I based on your 1992 MY, but did overlook your truck also uses the older style vacuum-servo speed control system. Looks like Bill has the updated info for you.

 

The MLP cannot set a code 452. That code is what is causing this problem.

Ford NEVER made MERCON fluid. Ford licensed others to make MERCON fluid. Ford discontinued licensing MERCON is 2006, so NOBODY has made MERCON since 2006. You can still find fluid labeled DEX/MERC, but it isn't MERCON. It may or may not meet MERCON specs. The correct fluid now is MERCON V.

You might as well jack up the front end and check the wheel bearings. Just like the transmission, they also CANNOT cause a code 452, which is your problem. Checking the trans pressures is a fun exercise, but it will NOT help you find out what's wrong. The code 452 is your entire issue. When that code is set the transmission line pressure is set high. The harsh shifts prove this. Checking your pressures with a gauge will confirm this, but won't help fix anything.

This is a list of what is causing your problem. Anything else may be fun to do, but one or more of these four things are causing the code 452, which causes the trans pressure to be high and makes for harsh shifts. If you are checking anything but these you are not working towards fixing the problem.

 

I unplugged the speed control sensor. No change. It had 2 plugs going into it. I matched up the color codes for the wiring and pulled that plug first, test drove and then pulled the other plug and test drove. No change on either, I plugged them back up. Just to be sure here, each step I try would produce an instant change correct? Meaning I wouldn’t have to drive for so many miles or drive cycles or have to unhook the battery or clear codes between each step, right? Since this truck has a new PSOM and new PCM I can look towards the ABS sensor or wiring, correct? If I unplug the ABS sensor(which is along the inside of the frame rail under the driver’s feet right?) would that be sufficient or is there an operational test for it? I have gone over the wiring harness on this thing in these areas a few times now. I have not seen one even questionable area. The whole harness seems to be tucked away in the plastic sheath and for the most part all taped up. I can find no signs of rubbing or wear and tear.

 

The ABS/DSS/VSS are just different names for the same rear end sensor. The harness for the sensor does run down the drivers side frame rail.
Not sure where you saying to unplug it but the resistance value of the sensor should be about 1400 ohms.