Bouncing Speedometer Needle
Bouncing Speedometer Needle
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Bouncing Speedometer Needle
1995 Ford F-150 2wd 4.9L bi-fuel. Does anyone have the proceedure on how to determine if the speedometer or the transmission transmitter is bad? I don't have a manual and can not find anything on the internet on how to determine which one is bad. My speedometer needle bounces and the closer I get to 65-70 the wilder it bounces and starts pegging out. When I'm running on gasoline and the needle pegs out it shuts the fuel off until the needle drops back then the fuel comes back on very irritating. I took a trip a few weeks ago and after about 300 miles the speedometer started working normally, but as soon as I stopped for gas it started bouncing again. On my way back home it started working after about 5 hours, but only until I turned the key off. HELP!
Post Fiend
Joined: Mar 2002
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From: Bonita Springs FL
The sensor is in the rear axle, it's called the VSS (vehicle speed sensor). You can try taking it out and cleaning it off with a rag, and if that doesn't work, you'll have to replace it. Next time you have the rear cover off for a fluid change, inspect the gear for broken or chipped teeth.
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Joined: Jan 2001
Posts: 2,358
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From: Nebraska
Your symptoms sound just like a bad speedometer head (PSOM). Especially if you develop a spot at around 1-2 mph where it wants to die, this is the speedometer giving a bad signal to the computer like it's pegging out. Do a search here for PSOM problems, it's a fairly common problem. But I would check the VSS first, maybe it's just that.
Post Fiend
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From: Topsfield, MA
The VSS is a simple magnet that gives off a pulse signal, its so simplistic they practically never fail, as long as its clean. Intermittant speedo needle jumps at all speeds (but never more than 20-25 mph jumps) are sometimes caused by the tone ring on the differential carrier. They could also be caused by a bad wiring between the sensor and the units they go to. If you've got that sweeping needle when you get past 65, and it bounces up past 85-90, and you've got a slight hesitation or dead spot in the engine when the vehicle is traveling 2-3 mph, it is most definitely a bad speedometer module.
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Bouncing Speedometer Needle
All the wiring appears to be in good shape. I bit the bullet and bought a rebuilt unit from DashUSA.com. The owner went through all the symptoms and one was if the tone/exciter ring is bad the anti-lock brake light will usually come on. Since it is run on natural gas most of the time the low 2-3mph problem doesn't show up. The natural gas is injected into the air intake hoses midway between the air filter and the throttle body and not through the injectors, or at least for this year.
I did notice when I took a trip a few weeks ago when it had run out of natural gas and it was running on gasoline it was a bear to get it going without it cutting off. I was in a driveway and everytime I would put it into gear and start moving it would cut off. It took several times, but I was finally able to get it going. We'll see if the speedometer is the problem that is what it sounds like. Figure while I have the dash apart I might as well see if I can find a pod with a tach and switch it over. That way I will have an extra speedometer if I ever need one. I'll post a follow up when the new unit is in.
I did notice when I took a trip a few weeks ago when it had run out of natural gas and it was running on gasoline it was a bear to get it going without it cutting off. I was in a driveway and everytime I would put it into gear and start moving it would cut off. It took several times, but I was finally able to get it going. We'll see if the speedometer is the problem that is what it sounds like. Figure while I have the dash apart I might as well see if I can find a pod with a tach and switch it over. That way I will have an extra speedometer if I ever need one. I'll post a follow up when the new unit is in.
Post Fiend
Joined: Nov 2001
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From: Topsfield, MA
Originally Posted by bleueyes
I did notice when I took a trip a few weeks ago when it had run out of natural gas and it was running on gasoline it was a bear to get it going without it cutting off. I was in a driveway and everytime I would put it into gear and start moving it would cut off. It took several times, but I was finally able to get it going.
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Just a note of thanks to all for their help, the new speedometer works great and the article on changing over to an insturment cluster with a tach helped greatly with the installation.
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Joined: Jan 2004
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From: seattle metro
Thanks to all of you for this thread. I just started having a "jumping" speedo and a rear abs warning light. I'm having no other symptoms, however, so I'm going to hope it's just a dirty VSS - I'll look tonight and get back to ya'll..thanks again !
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Joined: Feb 2005
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From: Pulaski, TN
try draining all the fluid out and clean out the diff. real good and wipe off the sensor and the drain plug. i had the same problem and i replaced mine and cleaned mine out but not very good. it helped for a little while. it never hurts to change the fluid and clean it all out any how. i really don't belive it is the speedometer because alot of people have this problem, but i could be wrong, so let me know if you get it fixed
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From: seattle metro
Apparently this was a symptom of a much worse problem in my case. Yesterday morning before I left for work my daughter called me - the truck 'died' . On the way to work I went to it on the side of the road - grinding noise in all gears (d/2/1) but reverse was ok. It was a pretty sickly metallic sound. Had to have it towed to my garage - the entire rear end/diff was shot. Ouch - It should be ready tomorrow...
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From: seattle metro
Got the truck back after the whole rearend was replaced (innards)... All is well except my wallet is lighter.
And on the way home guess what isn't bouncing ? My speedo. Apparently in my case it was the rear end on its way 'out'...
And on the way home guess what isn't bouncing ? My speedo. Apparently in my case it was the rear end on its way 'out'...
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From: Pulaski, TN
that is what i expected, that was my problem but i replaced mine myself and didn't clean it out good enough, that is why mine is still bouncing, they probally cleaned it real good, i am wanting to say it cost me about $150, how much was yours since you had labor to pay for?
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From: seattle metro
My entire rear end/posi , etc was replace - $1400. My mechanic is a small shop with 3 mechanics. I found them because our local NAPA uses them to turn rotors. I've been over there a few times and looked at the shop. He showed me the entire assembly, or what was left of it. There were little gears actually broken in half. Most of the gears looked like the were ground out and horribly stripped. There was also a big assembly in there, about the size of a big softball. It was a very solid, heavy piece of metal, except that it had a big crack right down the middle. I actually took some of the pieces home for the heck of it. I'm really glad I opted to tow the truck there. When I was there on the side of the road after my daughter I considered trying to drive the 5 miles to my mechanic, but decided not to. If I had and it locked up, I imagine i'd be paying for a new drive shaft or Xfer case..