Hello,

I am having some problems with my speedometer. I searched for all kinds of solutions but it seems like my problem is different.

The speedometer and the odometer only works for a little bit when I am not pressing the gas pedal especially when i shift down at higher RPMs.

I took my car to a "car's electrician" and he tested everything. In the end he told me that the problem was the speedo gear inside the gearbox. He showed me that when we remove the VSS and spin it with a drill the cluster works fine so I took the car to a mechanic and he opened the gearbox's tail but the speedo gear there is ok.
I tested the VSS at home and it looks like is working fine. (210 ohms and 0-6.6V) besides we tried another two used VSS and they didn't work too.
We also replaced and cleaned the grounds near to the engine.

Another thing that could be related is that the idle is too high. When I start the engine it doesn't go bellow 1,500 RPMs. After sometime when the engine gets hot it goes to 1,100 or 1,000. I believe it should be at 850 RPM, shouldn't it?

The car will go back to the electrician next week but he has no idea what it could be so I am praying that someone here knows what is wrong or what else I need to check.

The car is a 1997 ford ranger 4.0L with manual transmission.



PS.:I am Brazilian so as you noticed my English is not perfect, sorry.

 

As for the idle, you have a vacuum leak.
Yes, after engine is warmed up idle should be 750-800rpm
IAC(idle air control) Valve is working because idle drops as engine warms up.


VSS signal goes to a few things and Speedometer is as the end of the line.

The Pink/Orange stripe wire on the VSS is the Ground, but it is spliced to 2 other Pink/Orange stripe wires, one for the computer and one for the Cruise Control.
At that splice this wire is Grounded to body or Frame, Speedometer needs this Ground to work

Other wire on the VSS is Grey/Black stripe, it is also spliced to 2 other Grey/Black stripe wires that go to computer and cruise control.

If you have cruise control test it if works and stays at the correct speed when set, if not then problem is in the wiring between VSS and the two splices, assuming VSS is good as you suspect.

Or if no cruise, hook up OBD2 reader/scanner and select VSS, then either drive truck and watch for steady speed, or jack up the back wheels and watch for steady speed.
If speed/signal drops or changes unusually then problem is in the wiring from VSS to splices.

If cruise works or OBD2 show steady signal then problem will be from grey/black splice to speedo or VSS ground.
Problem could also be in the dashboard itself, cluster wiring can fail.


From the Grey/Black wire splice there is just 1 wire that splits and goes to GEM and speedometer, so speedometer doesn't get Ground signal directly from VSS, see above.
Pin 1 on dash connector, Grey/Black wire, is the VSS signals "end of the line".

So for speedo/odo to work VSS needs to have a good Ground, and speedo/odo in dash does as well.
And speedo/odo needs the Grey/black wire signal from VSS.
Test Pink/Orange wire at VSS with OHM meter to Frame, should be 0 OHMs if there is a good Ground on that wire


Computer and Cruise do not need the VSS to be Grounded, they are connected directly to the Pink/Orange wire.

 

Thank You RonD!

The car went back to electrician yesterday and I gave him your reply. Once he figure it out what is wrong I will post it here.
I had a quick look in the weekend and found a couple wires exposed. I covered them with electrical tape and putted another ground on the sensor (pink/orange wire) but it made no difference.

I also checked for vacuum leaks in the intake but I couldn't find anything. I am not worried about this now but it looks like it is getting worse.

 

I finaly got the car back from electrician (3 months later). The issue was an exposed wire behind the engine. At some time in the past, someone serviced the engine and didn't fixed the wires properly behind there so the engine's vibration damaged the wire's isolation.
With the problem solved the idle is working better now. It is still a little high (~1000rpm) but it is very stable, no oscilations. I sent the car to a mechanic to work on the suspension now and i will drive it a little bit more before consider this another issue.

Thanks for your help!!