I have a '92 F250 I got cheap. It is not shifting right.
The Tach and speedo both do not work, yet the other gauges do.

It seems unlikley that both sensors died at the same time.
I have not had a chance to get access to a wiring diagram yet.

I am curious if the sensors could work and supply the computer with needed information even when the gauges are messed up.

Secondly I am hoping to find out if there is some wiring in common between these 2 guages or sensors that I should look at.

Any ideas out there?

 

Can you give a little more information about not shifting right? Is it not shifting at all, does it engage at all when you put it in gear, is it shifting back and forth between gears at a given speed, etc.?

Also, it would be good to know, if it shifts at all, whether or not there's any slippage between the shifts, chattering sounds, harsh shifting, etc.

 

It seesm to shift real late, and shifts ok if I do it manually.
I don't feel any slipage, chatter, or sounds. The shifts are pretty firm and delayed.

 

Sounds like a bad vss sensor. If your truck has a speedo cable, it will be at the transmission end of the cable, if not, there will be a sensor on the rear diffy.
What does the fluid look like?

 

Throttle position sensor could also be the culprit.

 

It could be a VSS but that wouldn't explain why the tach is dead, too. It's certainly possible that both sensors are bad, but if the tach and speedometer quit at the same time, it's unlikely. The tach receives its signal from the engine speed sensor via the PCM.

The transmission's PCM gets inputs from both the tach and VSS, as well as the brakes, your turn/stop/hazard lamps, transmission oil temp sensor, and the shifter position sensor.

It sounds like your PCM is dead, but it may not be bad, it might just not be getting power. It gets power two 20A fuses, one that's hot all the time (Fuse I in the engine compartment fuse box), the other is hot in the start and run positions (fuse U in the same box).

On the PCM wiring harness, pin 1 (yellow wire) should have 12V all the time. Pins 37 and 57 (both red wires) should have 12V when the key is on. Grounds are on pins 20, 40 and 60. If you have power on those pins and your grounds are ok, your PCM might be defective.

To answer your question, I think the sensors could work and supply the PCM with its inputs if the tach/speedo were dead, but since your transmission is not shifting as it should, I'd hazard a guess that your PCM is not getting those inputs. The fuses and wiring I mentioned above should help you isolate that, or at least get started.

 

well at most if i have learned anything from this site its that the spedo and the tack are required to be working if you have an automatic. yea thats just about it

 

i'm a d-a** and i understood that.

 

Well, I'm a technical writer, so it's kind of my job to look at schematics and wiring diagrams and come up with a functional description.

I could tell you what I write about every day, but I'd have to kill you.

Ha ha, just kidding. I write tech manuals for the navy's Aegis Weapon System.

 

Those E4OD's are tricky devils everything works better when it is electronically controlled. Yeah Right! My C6 runs nice and is hard to screw up vacuum lines. Would like to have a standard again but for plowing unless you have long runs your HULK leg weighs 30 lbs more from shifting.

Check your fuses that would be a good start. Plus the TPS and Tach sensor are nearby each other and share the same harness routing something easy might even exist other than the fuses.

 

sorry i'm just an independant wrench that depends on this kind of info to troubleshoot, so when i get a pin# wire color or flow chart i'm thrilled but when someone can tell me where to go look and help me out with specifics well he might just get invited to next beer-b-que

 

I had the same thing happen to me last year, just after I had put in some extra gauges.... Turned out that I had blown a fuse. Mine had the same symptoms, no Tach, No Speedometer, and transmission that wouldn't shift or if it did shift would knock your teeth out. It was one of the fuses inside the cab to the left of the steering wheel. New fuse and no problem.

 

I found one that was blown, but replacing it did not help.
Anyone know where I can find a guid to the fuses? I do not know which one is which.

 

Nevermind I found the fuse panel door and it has the key. It looks like all fuses are ok.
I am going to pull the engine and put it in my '91 so I don't need to make this tranny work, but it woud be nice.

 

Now the tach is working.
With only 1 non-functioning gauge, my search is narrowed down!