I have a 2000 F150 4.2 manual trans and the speedometer is acting up. I turn it on and the speedometer starts jumping around (while parked). The idle is fine the ABS light is off. When the speedometer eventually jumps to 100 the truck struggles and likely stalls. I can go forawrds and reverse fine, but the speedometer still jumps... hits 100... and stalls.
I don't want to drive it anywhere because I don't want it to die while I'm driving.

To troubleshoot:
- I've disconnected the speed sensor at the rear diff: Speedo still jumps and ABS light comes on.
- I've disconnected the sensor at the transmission with no affect.
- All the other gauges are functioning normally including the Odometer.

If this is a sensor issue that's easy to fix, btu it seems more like a speedometer issue.

Can anyone help?

 

Look up hidden gauges 2000 f150. Iirc you hold the odometer button down and then start your truck. There should be a speed setting on there. You cycle the settings by pressing the odometer button. When the speedo jumps does the readout jump too?

 

OK. When I ran the test the enG and m displays jumped around with the needle indicator. The truck stalled several times so I must have run this test mode a half dozen times.

I let is sit for 10 minutes and tried it again. Needle stayed at 0 and so did enG and m.

I have the big workshop manuals and dealer test mode is on page 413-01A-8

 

Do you have the torque app? Or any way to read the speed before the cluster?

 

Don't know what that is so I'm sure I don't have it. Previously, I disconnected the sensors at the trans and rear diff and the Speedo still jumped around. I expected that if I disconnect those two inputs the Speedo would read zero. Right?

 

Same thing happened on my uncles '00 F-250, turned out to be the rear speed sensor. You said you disconnected it, did you pull it out to look at it? My uncles had a chunk of solidified diff fluid stuck to that messed it up. If you haven't, I'd try to pull it out and clean it.

 

Thats why im thinking if you have a smartphone and order a wireless Bluetooth dongle for your obd port we can see if you are getting true speed readings to the comp.

That would eliminate any problems in the sensors or wiring and even the output from the pcm. Leaving only the gauge cluster to be at fault.

 

I just ordered the Dongle from amazon, thanks for the tip - looks like a useful devise. this is the first electrical problem I've had with the truck, all other repairs were self evident.
As of today the problem has gone away. Does the dealer mode somehow reset the gauges? I don't believe that any fix would be that easy, but it would be cool.
I'll post back after I get the dongle.

 

As far as I know it doesn't reset anything but I love mine. The dongle stays plugged up and ive been debating on a tablet to always keep an eye on things.

 

Red-Ford -
Early on I pulled the rear sensor and it had some solidified oil on it, I cleaned that off and reinstalled, and the problem persisted. I'll definitely replace both sensors before touching the gauges... both sensors under $20 each.