electronic speedometer

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never2old2learn-ron

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The speedometer on my 94 ford f-150 has been malfunctioning for awhile now. It will be fine for several miles, then it quits. It may start working right away or it may stay at zero for miles. then it will kick back in. Lately, it has been doing it alot. Could it just be a connection or what? I admit I know nothing about electronic speedometers. Any ideas? Thanks Ron
 

Calman

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Ron it could be the sending unit on the transmission.It's an electro magnit and lots of times metal particals from the tranny will collect on it and cause it to malfunction. I would pull it out and clean it and while your at it see if it's got current to it. Some models you have to turn on the ignition and put it in drive before you can test it.It should be magnatized when you do this.If not you have some electrical problems.
Hope this helps.

Cal
 

Aaron

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Look at the top of your rear axle, in the middle. You should see a piece of plastic with a pigtail and a set of wires following to the frame rail. Unplug the plug (snaps on two sides of it) and pull it off. What is left is a sensor that is attached to the axle with a small bolted bracket. I think it is 8mm or 10 mm bolt (might be bigger). Take a wire brush and clean all the dirt around the sensor. Take out the bolt and pull the sensor out..might be rusted in tight..might have to wiggle and turn it. It has a magnetic plug at the end that contacts the ring gear in the differential. Check to see if there are metal shavings stuck to the end of it. Clean it off well and reinsert it. Let me know if this works. :cowboy:
 

Calman

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Well you can tell i'm certainly not a ford man.On GM the sending unit is located on the tail housing of the tranny. :lol: :lol:

Cal
 

grannysoo

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And if none of that works, you may have a bad speedo that you need to have rebuilt. Chevy has a big problem with this.
 

Aaron

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grannysoo":2hg64ir5 said:
And if none of that works, you may have a bad speedo that you need to have rebuilt. Chevy has a big problem with this.

Oh, we'll figure this out. I spent a few weeks last fall working the bugs out of my speedometer. As long as it's a Ford and you have a wrecker nearby that you can get cheap parts from, I can help you figure this one out. :cowboy:
 
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never2old2learn-ron

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I pulled that sensor and checked and cleaned it. There didn't seem to be anything on it. I checked it for continuity and that was ok. I checked the plug-in and there was current there. Put it back together, but still not working. We will be busy for awhile now, so don't know when I can get back to it. But it's no big deal. As long as I got a tach, I know pretty close what the speed is. In the old days, most of my speedometers didn't work right anyhow.. I'll let you know if I figure it out. Aaron & Cal, thanks for the help. Grannysoo, you may be right about it needing to be rebuilt or replaced. Ron
 

Aaron

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never2old2learn-ron":2ahe97o4 said:
I pulled that sensor and checked and cleaned it. There didn't seem to be anything on it. I checked it for continuity and that was ok. I checked the plug-in and there was current there. Put it back together, but still not working. We will be busy for awhile now, so don't know when I can get back to it. But it's no big deal. As long as I got a tach, I know pretty close what the speed is. In the old days, most of my speedometers didn't work right anyhow.. I'll let you know if I figure it out. Aaron & Cal, thanks for the help. Grannysoo, you may be right about it needing to be rebuilt or replaced. Ron

You got ahead of me. Ok, if continuity works then it has to be the Programmable Speedometer/Odometer Module (PSOM). It could also be the ring gear in the differential missing teeth, but that is pretty unlikely.

The PSOM is located specifically behind the speedo gauge and includes the odometer face. To get at it, you have to take the gauge cluster out. I can give you further info on how to do that if needed.

If you don't care what the odometer says, you can get a used PSOM at a wrecker or on Ebay. You just buy the entire gauge cluster and dismantle it from there.

If you want the odometer to be exactly, or roughly in range of your current one, you need to get the replacement calibrated.

I had to end up replacing mine. I went through here: http://www.dashusa.com/ford.htm
The owner, Steve Damore, is a great guy to work with. There is no core charge. For my truck, the cost was $287.00 USD for a replacement speedo that was calibrated for the mileage I already had on the truck. Mind you, mine is a diesel, so a gas speedo will probably be cheaper.

Good luck. :cowboy:
 

DiamondSCattleCo

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Before you start yanking speedometers, check continuity on the wires running from the sensor to the powertrain module. Wiggle the wires while checking continuity, as I've seen plenty of Fords with rotting harnesses back there. With the continuity gauge wailing away, wiggling the harness would simulate bumps and the continuity tester would blip. If that checks out buy a new sensor or use a sensor from a truck that you know works. They can develop intermitent issues and will sometimes function, sometimes not. They're nothing more than a Hall-Effect sensor, so they will lose magnetism over time, leading to intermitent functioning issues. Only after you've eliminated all of the above do you start digging into expensive modules.

Rod
 

JHH

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DiamondSCattleCo":1hc7xd5x said:
Before you start yanking speedometers, check continuity on the wires running from the sensor to the powertrain module. Wiggle the wires while checking continuity, as I've seen plenty of Fords with rotting harnesses back there. With the continuity gauge wailing away, wiggling the harness would simulate bumps and the continuity tester would blip. If that checks out buy a new sensor or use a sensor from a truck that you know works. They can develop intermitent issues and will sometimes function, sometimes not. They're nothing more than a Hall-Effect sensor, so they will lose magnetism over time, leading to intermitent functioning issues. Only after you've eliminated all of the above do you start digging into expensive modules.

Rod

I agree here. I would much rather bolt on a 25.00 part than a 280.00 part. Sorry Aaron. But I think it is the sensor in the rear diff as well. I have seen way to many of them go bad and be intermitant like that.The PSOM generally goes blank and wont work (Digital odometer) . JHH
 

Aaron

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Whoops. Was hammering that off in time to watch Mantracker. Should have mentioned that he should replace the sensor and maybe even the pigtail first.

The PSOM will not always go blank. There is really no prescribed rule as to how they malfunction. Some shut down entirely. But I have heard many that say they will work. Sometimes just the odometer and sometimes the speedo.

In my case (over the span of a few weeks), the speedo needle started jumping around. Then it would quit. Then it would work. For all that time, the odometer worked. Then one long drive and the odometer started to flash. At a couple points, the odometer actually was losing mileage (few miles). Then, for a period of about 40 miles in the same trip, everything worked perfectly, allowing the cruise control to work. Then everything died, including the odometer for a while, and then the next day, it all worked again.

I agree, its much easier on the mind and wallet to buy cheaper parts. But again, if I wanted to avoid all these problems I would just go and buy a new 6.4L. :cowboy:

If you don't fix the problems right away, you get to experience all kinds of fun things. :lol:
 

grannysoo

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Aaron":1mjq38v4 said:
grannysoo":1mjq38v4 said:
And if none of that works, you may have a bad speedo that you need to have rebuilt. Chevy has a big problem with this.

Oh, we'll figure this out. I spent a few weeks last fall working the bugs out of my speedometer. As long as it's a Ford and you have a wrecker nearby that you can get cheap parts from, I can help you figure this one out. :cowboy:

Are you saying that when you buy a Ford, you should buy 2 of them? One to drive and the other to have as a parts truck? :lol2: :lol2: :lol2:
 

Aaron

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grannysoo":10fk6qp6 said:
Aaron":10fk6qp6 said:
grannysoo":10fk6qp6 said:
And if none of that works, you may have a bad speedo that you need to have rebuilt. Chevy has a big problem with this.

Oh, we'll figure this out. I spent a few weeks last fall working the bugs out of my speedometer. As long as it's a Ford and you have a wrecker nearby that you can get cheap parts from, I can help you figure this one out. :cowboy:

Are you saying that when you buy a Ford, you should buy 2 of them? One to drive and the other to have as a parts truck? :lol2: :lol2: :lol2:

I suppose that is what it looks like. What I mean is, I am familiar with Ford trucks and provided you have a easily available supply of cheap parts from a wrecker, I can probably help you fix it.

Buying parts from a dealer can get costly real fast. I usually do this, as Ford parts trucks are rare around here (auto wreckers like them to sell to insurance companies for claims...BIG money) ..in which case I shop around Ontario, Manitoba and Minnesota to find the best deals on dealer parts, or on the web.

If your a GM or Dodge man, you're on your own.
 

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