I just bought a 1999 F250 4wd 7.3 with a little under 300k on it, 4R100 automatic that wasn't reliably shifting into 3rd gear. Truck has a hydraulic arm bed on it for feeding cows and has been severely abused, underside is caked in 2" of mud/hydraulic oil/etc. Trans supposedly was rebuilt about 20k ago, so I pulled the valve body and found a valve installed backwards and one missing the spring. I installed a Transgo Tugger kit while I was in there, along with one of their 2nd/3rd steel shift valves. When I put it in 4Low on the farm (electronic shift Trans Case), I can go through 1,2,3,4 gears using the shifter and everything feels fine. But in 2wd on the road it still doesn't want to go into 3rd if I manually select the gears. If I just put it in D and go, I feel like it stays in 2nd too long and jumps right to 4th but I'm not sure.

The speedometer hasn't worked since I bought the truck, and the only relevant code I pulled from it at purchase (using an AutoEnginuity scanner) is a P0500. I pulled the rear ABS sensor from the diff last night and it looked good, though the oil has plenty of water in it - so I'm picking up a new sensor and oil today in town. All fuses are good, and the rest of the dash works fine. No check engine lights, no ABS light, no flashing OD light. Just curious if anyone here has any advice on diagnosing the speedometer, as I'm thinking it is related the erratic transmission shifting. I've searched for wiring diagrams with no luck, so a little help with that would be greatly appreciated. Also curious if 4Low would disable the ABS system and allow the transmission to shift independently of the speed sensors, etc?

Any help would be greatly appreciated, thank you.

 

Nice! I love my AutoEnginuity scanner. On it, you should be able to see vehicle speed. Go to Live Data and select that parameter. Do you get a reading of vehicle speed?

If you get a reading, all the sensors are fine. Your speedometer gauge or the circuitry is likely to blame. If you do not get a reading, dig into the wiring and sensors. PM Sous (see his service manual thread). He has a software for the service manual with wiring diagrams.

 

Will do. Thank You!

 

Hey cfpinz, I got your PM and have reported for duty to get you some help if we can. The FTE is a great resource of great people and we just need you to keep talking and keep telling us what you are seeing.

Do you have a PC available to you? If so, post in this thread and I will get the Ford Service Manuals sent right over to you ASAP.

Free Ford Service Manual

If you have a PC and are able to install the Ford Service Manual, check out this thread for some great tips: Helpful Tips For Understanding Shop Manuals and Wiring Diagrams

If you are still having trouble finding what you need, do not worry, I still have trouble finding what I need and I have been rummaging around in that manual for a while now. Just let us know and we can get you sorted out.

You mentioned the rear ABS sensor, you are most likely referring to the VSS (Vehicle Speed Sensor) on the top of the rear differential. The 7.3L is very particular about sensors, so we generally recommend Motorcraft, International or Alliant if possible.

There are pinpoint tests from these components in the PC/ED section of the manual that you might want to glance at. A lot of times a multimeter is required and a decent scan tool like AE, so you are well on your way.

Again, we are here to help sir and glad to have you around.

 

You can even graph it. I was troubleshooting my crank position sensor below. The graphing on Giotto is only for live data, but you can record a data log. It saves a spreadsheet of data points taken over a unit of time. I found the time range of where my issue occurred and put it into a graph. This is not related to your current issue, but just general troubleshooting using AE/Giotto. You can see the sudden dip in speed and RPM, then the later dip in ICP. That's where my CPS was cutting out.

Select the data logging file to be in a location you will be able to find again, hit the record button, and then hit stop when you want it to stop saving data. Note that I have the Ford expansion package, but you should be able to see the vehicle speed in the generic powertrain module.

 

Thank you both, I'm headed out for the evening and will try and install the service manual on my home computer tonight.

Thanks again, I really appreciate it!

 

The third brake light can cause trouble with the speedometer. Might get lucky and see the wires are fried or something...

 

Wow. That's a connection I never would have made.

Thank You.

 

Sure thing

 

How does that exactly work? I have heard that mentioned before, but I don't see it on the wiring diagrams... The only possibility I can think of is if it blows a fuse for the GEM or something like that.

 

I replied to a PM from cfpinz just a moment ago, but thought I would include the answers here for future readers.

For the VSS, there is a pinpoint test labeled "DL" if you go to PC/ED>year and 7.3L>section 5 pinpoint tests>DL.

For the instrument cluster, there are tests and information if you go to workshop manuals>year>section 4:13 Instrumentation and Warning System.

For wiring diagrams, go to Wiring diagrams>components>year>starting letter I>Instrument cluster>then start digging.



The key to success when using the FSM is knowing the proper name of the part or test you are looking for. Also, navigating the wiring diagrams could be much easier, but this is free and 20 years old, so I am grateful.

For navigating tips, see the link below and learn from our mistakes and lessons instead of making them yourself.

Helpful Tips For Understanding Shop Manuals and Wiring Diagrams

 

So I learned it on my dad’s 96 PSD. The fuse for the speedometer kept popping and we discovered the third break light’s pos wire was frayed and so a heat shrink but connector on it, bata-boom bata-bing that was the ticket!
Now I know, I know, apples and oranges OBS and SD but I have heard of SD guys who had speedometer problems coming from the third brake light!
Might be wrong but pretty sure not!

So to answer your question, I have NO idea lol

 

I don't recall what the symptom was but I have read here where the unassociated third brake light was the culprit. It might have been the cruise control.

 

I lost cruise one time on my '97 7.3 truck because of a blown brake lamp, can't recall whether it was the 3rd or a bedside light.

Haven't had a chance to road test the '99 referenced in this thread yet with the computer checking vehicle speed and diagnostic tree, but will update once I find the cause of the issues.

Thanks again to all.

 

So I finally got the truck out of the shop and took it for a drive with the AE hooked to it. The speedometer doesn't move at all but AE Vehicle Speed Live Data shows the correct speed that I'm traveling. So I'm assuming the VSS and associated wiring is good because of this. The FSM directs me to Sect 308-07A, which is the 4WD system and I can't find any mention of speedometer diagnostics there. My 4WD (electronic shift) is working correctly, so I'm at a loss currently.

Any words of advice at this point?

Edited to add: Took the truck off the farm roads and the speedometer will jump to 75 mph and stay there as long as actual speed is 40 mph or above. Transmission will skip 3rd gear and go straight to 4th if using the D position, but will fall back to 3rd if you cancel using the OD cancel button. If you start off driving in D with OD cancelled, it will hang in 2nd until you disengage the OD cancel function and jump straight to 4th.