Speedometer mystery!!

Zeo · Mar 18, 2017

Hey guys

I've read a bunch for topics about speedometer problems yet I still can't track mine down.

I have a 2001 2wd ranger 2.5l. It's a old plain Jane fleet truck. The problem I have is that the speedometer bounces and falls to zero if I drive over 68mph. Also when the needle moves under 25mph at that time I can feel resistance like the a.c compressor is kicking on and off.
I have replaced the speed sensor on the diff twice and cleaned the under the seat plug 3 times. I don't know where to go now. Thinking it's the plug under the seat so I'm about to cut and solder all the wires together. There must be a electrical leak from the fuel pump wire bleeding to the vss sensor or vice versa at that plug.

Any info would be great thanks!!!

RonD · Mar 18, 2017

Welcome to TRS

Manual or automatic transmission?

Doesn't read like connector issue.

Speed sensors generate their own AC voltage, the "speed pulse" is the pulses in the AC wave form.
Fuel pump, or any other power wire in the truck, will be DC volts, so you would see other issues at speedometer if there was a wiring short, not just a dropped signal

In 2001, and up, the rear axle VSS(speed sensor) is only used for ABS, not for speedometer.
(this was only used from 1998 to 2000)

2001, and up, Rangers got OSS(speed sensor) on the transmission tail shaft, and it was used for speedometer, cruise and computer(PCM)

But, the 2001 4cyl Rangers were changed mid-year, 2.5l OHC Lima engine was dropped in mid-2001 and replaced by the 2.3l DOHC Duratec 4cyl engines.
So 2001 Ranger could have either engine, and maybe either speed sensor setup.

So what I would do is to unplug the VSS on the rear axle and go for a drive to confirm that it is the speedometer signal.

In either setup, VSS or OSS, the speedometer is not connected directly to the speed sensor
VSS would be connected to the GEM(module) behind the radio, GEM is programmed with stock tire size and would correct the "speed pulse" for tire size then send that AC pulse out to speedometer, cruise and PCM.

OSS signal would go to PCM, which would be programmed for tire size and rear axle ratio, PCM would correct the signal and send that AC pulse out to speedometer and cruise.

The electronic speedometers use an electric motor.
Odometer also uses a separate electric motor.
When speedometer drops above 68MPH does odometer also stop?
If not then speedometer itself is the problem, not the speed signal

As far as the engine:
Is the AC on or the Defrost(AC also on), when you feel the power loss, or power pulse?
If so then turn off AC and Defrost, and see if it still does it, you could just be low on refrigerant so compressor is cycling on and off.

Zeo · Mar 18, 2017

I have a 5 speed. I don't remember there being a sensor on the tailshaft

RonD · Mar 18, 2017

Rangers had them from 1983 to 1997(speedo cable/VSS hookup), then they were gone from 1998 to 2000, then back again in 2001(OSS only)

But as said yours is a transition year, 2.3l Duratec would for sure have the OSS.
Just not sure about the 2001 2.5l

Check if Odometer also stops when speedometer does.

Zeo · Mar 19, 2017

Yes the odometer and trip meter stops when it goes to zero. I looked under my truck and I didn't see anything going into the transmission besides my hydro clutch cable. Maybe the 3rs VSS sensor is bad (it was only $10). The last one i replaced would read up to 75mph, this one only reads to 68.

Speedometer mystery!!

Zeo

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