Hello, I have a 1993 f350xlt crewcab dually, 7.5l e4od, 131000 miles. About a year ago the cruise control stopped working, the speedo-tach-odometer works good. I got in the truck the other morning put it in reverse and backed out of the driveway (reverse worked good) put it in drive the tranny slipped trying to move forward but wouldn't, so I put it in 1rst in it engaged normal so I started down the road and manually shifted to 2nd it shifted to 2nd and I continued to pick up speed and manually shifted into drive and it acted like it went into neutral, so I manually downshifted to 2nd and it engaged so I increased throttle to 3000 rpms and manually shifted to drive, it engaged very harsh, I got it to 45mph and od engaged. From that point on it shifted through all the gears but very harsh, the od light did not blink but I could tell it was in limp mode. I went to the parts store and they told me to replace the vss on the diff. I replaced vss plus I replaced the solenoid pack, filter and mercon v fluid. The pan looked great the fluid was very clean and the magnets looked good with no shavings at all. I test drove it and it stayed in limp mode again no blinking of light. I checked the codes and it gave codes 29 and 31. I cleared the codes with code reader then disconnected the battery for several minutes, hooked it back up and test drove it again. It slipped in drive again, so I put it in 2nd ran it to 3000 rpms the it hard shifted to drive...Back in limp mode again with no blinking of light. I replaced the pcm about 2 years ago with a new one. I have checked wiring and connecters back to front, I have checked grounds, I pulled the psom it looked good, no bulging leaking caps, no burnt areas so I put it back in (speedo-tach-odometer works good). I opened up the pcm everything looked good but I replaced the caps for good measure. It's only giving code 29 and 31 again so I assume that the tps and the mlps sensors are ok as it's not giving codes that lead to them. I'm not sure what to do next, sorry for the long post, can anyone give me some insight as what to check next. Thanks in advance.

 

I forgot to mention, I did disconnected the cruise control connector test drove and it made no difference, the cruise control stopped working about a year ago, I replaced the switch below the master cylinder but it still didn't work. Thanks

 

A 1993 with a E4OD and a 7.5L will not give codes 29 and 31 with the right PCM for the truck. It would have three digit codes.

If you are getting these two digit codes with a code reader then they sold you the wrong PCM Computer.
And then the 29 would mean you have a bad signal from the PSOM to the PCM. You say the speedometer works OK so that means you have a good VSS and the parts place told you wrong about replacing the VSS. They very seldom go bad.
Then 31 code has to do with the EGR valve not working right but that would not cause the problems you are talking about.

What is the calibration code on your drivers door post?

The code in the below photo at the end of the arrow is "3-98A-R00".

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Hi subford, I've read many of your posts, thank you for the reply. The calibration code is 2-98A R10.

 

That number goes with a 1992 Truck and not a 1993.
The PCM for that Eng. number is F2TF-12A650-JB.
Or the part number is :F2TZ-12A650-JB

 

Your right! I checked the the driver door sticker and it was produced 8/92. It's titled as a 1993.. I will pull the pcm and give you the numbers so you can tell me what it belongs to. I'm going to pull psom back out also an check continuity from the psom connector to the pcm connector. Does the wire from the psom go to the cruise control before it goes to the pcm? I'm just wondering if the fact that my cruise control stopped working has something to do with messing the signal up going to the pcm?

 

I pulled the pcm, the number is: F2TF-12A650-JB. I'm not sure why it's giving 2 digit codes, I have checked several times and I'm getting 29 with the code reader. Last night I found a psom reset procedure so I did it then cleared the codes on the pcm, took it for a test drive and the transmission is still in limp mode, but no code 31 anymore, just code 29 now.

 

Guessing you have the 1993 layout under the hood with the electronic speed control and not the vacuum control one.
The wire from pin #7 of the PSOM goes to Splice 246 (S246) located in the main harness, near T/O (Take Out) to speed control amplifier. The n the wire goes on to the PCM.
So no the wire does not go to the Speed Control and then to the PCM. Instead it "T"'s off.



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Yes it's the 1993 layout (no vacuum). Thank you for the schematic. Have you ever heard of a psom going bad (vss signal) while the speedo-tach-odometer is working good?

 

Yes I think we have had one or two have had the bad (vss signal) while the speedo-tach-odometer was working good.

Here is an example in a PDF.
http://www.atraonline.com/gears/2007...2007_01_04.pdf

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Thanks for the PDF subford, excellent read indeed. I've checked the wiring and connectors from psom to pcm and all's good. I hooked my dvm (+) to the gray/black at the cruise control connector and the (-) to the body ground and test drove the truck. As soon as I started rolling (about 5 mph) it jumped from 0 to 4.7v and stayed there no matter what speed I reached. I stopped and moved the dvm dial to hz. It read 005 to006 no matter what speed I reached. If I did test right it would indicate a bad psom even though the gauges work perfectly. Btw, what is the calibration sticker on the driver's door for? Thank you very much for your help as I wouldn't​ have made it this far without your help.

 

It tells what the part numbers are for parts that are specific to your trucks set up.
For yours the below chart.


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Thanks for the chart subford, that's good information to have! Well I guess I didn't diagnose the problem like I thought.. I got a good psom from a working 1994 f250 4x4. I got it installed recalibrated to 1031 for my truck, erased the pcm and took it for a test drive.. it didn't fix it. When I got back I checked for codes and got 29 and 31....again (damn truck is gunna cause me to drink hehe). I'm going on Monday to get a good used pcm from a 1992 f250. I got a guide to try to diagnose my cruise control problem also, I'll wait until I get the pcm swapped out to see if that helps. I'm trying my best to diagnose this but at this point I'm just throwing parts at it.. Good thing I love my truck or at this point I'd take a BFH to it lol.

 

Hey subford I got it fixed!!! I installed a pcm from a working 1992 f250 with the same model number as the one I had in it, cleared any codes that were in it from the previous truck, took it for a test drive of about 10 miles and I could hear the Angels sing!!! It runs awesome again!!! I brought it back and now I'm just getting code 31 and the cruise control still doesn't work. I'm gonna track down 31 and diagnosis my cruise control and I should be good to go. Thank you for your help, I have down loaded everything you posted for future reference.

 

A CM Code 31 indicates that the EGR valve was closed further than normal or EVP sensor or circuit has failed with an intermittent low voltage sometime during vehicle operation.

If it is an KOEO code then Service Code 31 indicates that the EGR Valve Position (EVP) sensor signal is less than the Self-Test minimum value of 0.2 volts.