I have a set of problems that all seemed to begin at one time. Just after replacing the alternator successfully, both the odometer and speedometer stopped operating. Also, the F150 started automatically shifting with a large jerk. The odometer is an electronic display that is now blank. The speedometer reads solid at zero with no action. Does anyone have any ideas just what may be causing all this to happen at once?

 

Hello- Welcome to FTE! I have moved your post to the specialized forum we have here for your question. Check out the list of tech forums we have on FTE. There is a wealth of information and expertise here to help you. There are a number of links in my sig below to help you also. Have fun!

You may have damaged the engine computer with some electrical spike caused by an improper connection.

 

You are not getting a signal from the VSS sensor in the center top of the rear end. The plug came off, VSS sensor bad, ....

 

If your your dome light is dead as well, you may have blown a fuse..check the fuses.

 

Really? Are these speedo's not cable operated?

 

Yes really.
No they are not cable operated.
The transmission is shifted with information from the EEC.
The EEC gets its information from the PSOM.
PSOM gets its information from the VSS.
PSOM - Programmable Speedometer/Odometer Module


DESCRIPTION AND OPERATION

The electric analog speedometer receives its input from the anti-lock brake sensor. The liquid crystal display (LCD) odometer is a combination trip odometer and total odometer. The total odometer is normally displayed. To see the trip odometer, press and release the SELECT button on the upper right side of the speedometer. To zero out the trip odometer, press and release the RESET button on the upper left side of the speedometer while the trip odometer is displayed. If the trip odometer is displayed, press and release the SELECT button to return the display to the total odometer value. The speedometer, containing the trip odometer and total mileage odometer, is serviceable only as a unit. An instruction sheet is included with service units for setting odometer mileage.

The speedometer is also used to provide a speed signal for correct operation of the vehicle's EEC module and speed control (if so equipped). Because of this, it is VERY IMPORTANT to change the speedometer's internal conversion constant if the size of tires on the vehicle is changed. Changing the conversion constant to the proper value when the tires are changed will also make sure that the speedometer retains the original factory-set accuracy. The conversion constant can only be changed three times once the vehicle leaves the factory.

 

I was pretty sure that there was no speedometer mechanical cable but now comes some questions. First of all, thanks must be extended to all who have added to the "thread". Basically, it would seem we have the following items in question: the VSS (Vehicle Speed Sensor), located on the top of the transmission and the EEC (Engine Electronic Control), the PSOM (Programmable Speedometer/Odometer Module) and of course the ECM (Electronic Computer Module). I would guess that the PSOM is part of the intsrument cluster, etc., but where are the ECM and the EEC located physically? Second question; which is most likely the faulty unit? Further, I understand that "fuseable links" are used in the system, instead of circuit breakers or fuses per se. Is there one of these "critters" that just might have depowered any or a combination of these units? I have a number of factory and other books on the vehicle but these points are not clearly covered.

Thanks again,
Phil

 

1. The VSS (or DSS) is NOT at the Transmission, it is in the center top of the rear end.
2. The EEC is the Computer, the ECM was used in the early 80's and was their Computer. Located LH side of safety wall, left of main harness connectors (A9).
3. The PSOM is a small Computer in the instrument cluster that the Speedometer and Odometer plugs into and sends information to other Modules.
4. You have some fuse links but they are in the main power area and if they were bad you would not run at all. All of the items in question have fuses.

Here is a diagram of the Speed Sensor System:

http://i54.photobucket.com/albums/g9...peedSensor.gif

 

ECM, PCM, ECU, EEC are all various ways of talking about the engine computer on these trucks. Some higher end vehicles may separate these units, but these terms can be used interchangibly when talking about trucks like ours.

 

Thanks again for the information. In a search for the above EEC (Engine Electronic Control) I noted, mounted in the engine compartment, on the left side and mounted on the inner left inside of the auto body, a sort of "heat sink" looking device (about 3 X 4 inches) with a single multiple connector. Is this the EEC? Further, I located the Power Distrubution Box, which contains numerous "plug in" fuses. All these are NOT labled (except for amperage), and all checked out absolutely with NO failures. How does one contain a tabulation of each fuses circuit, and is the "heat sink" type device, the EEC? As said before, I have numerous books (some Ford vehicle documents in multiple volumes). None of these direct one to the facts of the issue. Are there volumes to be found that are detailed, with theory of operation and schematic diagrams?

 

No, that is the ICM (Ignition Control Module) aka TFI Module (Thick Film Ignition system), The EEC is located LH side of safety wall, left of main harness connectors (A9), low at the outside, big plug with bolt in center. Look very close at the underside of the lid.Yes, they are from Ford (HELM Inc.)

I can post links to some diagrams and theories if you tell what area you want to look at.

email me

 

Thanks again "subford". As to the Power Distribution Box and the underside lid, there is a series of refrence numbers given but no actual asignment to specific circuits shown. However, in the Owners Manual there is a reference of sorts but I do not think of it as specific.

As to the Helm Inc. web site, they show nothing for vintage 1992.

Finally, as to emailing you, the FTE does not allow that unless one has at least 15 days of membership and/or I believe, a total of 50 posts.

I would be very thankful if you could provide direction or whatever to theory of operation and schematic diagrams for any or all of the units associated with this "thread". That would be: VSS (or DSS), EEC (old ECM, PCM or ECU) and PSOM along with RABS (Rear Anit-lock Brake System) module.

Phil

 

Not true, I just went there, they have it all.email me at subford(AT)gmail.com Replace the (AT) with @

I need more information about your truck.
What engine?
What Transmission?
4X4?