Jumpy speedometer 4.9L M5R2 2wd
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Jumpy speedometer 4.9L M5R2 2wd
I am trying to figure out a troubleshooting path for my jumpy speedometer. I've lived with this issue for many years and have replaced the RABS on the rear differential and tried a different instrument cluster but neither fixed the problem.
I also put a new connector on the end that connects to the RABS sensor. I was trying to clean this connector recently and damaged the one I had put on and ended up having to drive the truck without the RABS connected so I left the wires hanging without the connector on. While driving on the freeway I noticed my speedometer was going from 0-5 MPH! I drove 200 miles like this and the speedometer only did the 0-5 MPH for a short time, say 20 miles or so.
Does my transmission have a VSS that I should try replacing? The wires that go to the RABS, where do they go to next? Any suggestions on what could be causing this? I am fairly certain the RABS and instrument cluster work correctly.
I also put a new connector on the end that connects to the RABS sensor. I was trying to clean this connector recently and damaged the one I had put on and ended up having to drive the truck without the RABS connected so I left the wires hanging without the connector on. While driving on the freeway I noticed my speedometer was going from 0-5 MPH! I drove 200 miles like this and the speedometer only did the 0-5 MPH for a short time, say 20 miles or so.
Does my transmission have a VSS that I should try replacing? The wires that go to the RABS, where do they go to next? Any suggestions on what could be causing this? I am fairly certain the RABS and instrument cluster work correctly.
Post Fiend
Joined: May 2004
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From: Lakewood, Ohio
manual says to check these thing if speedo jumpy.
check for presence of the following conditions:
damaged missing or bent teeth
metal chips on speed sensor
open or shorted sensor
improper gap between sensor and speed sensor ring
i will add: change the rear gear fluid
check for presence of the following conditions:
damaged missing or bent teeth
metal chips on speed sensor
open or shorted sensor
improper gap between sensor and speed sensor ring
i will add: change the rear gear fluid
Last edited by quicklook2; Jul 13, 2006 at 01:19 PM.
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Originally Posted by quicklook2
manual says to check these thing if speedo jumpy.
check for presence of the following conditions:
damaged missing or bent teeth
metal chips on speed sensor
open or shorted sensor
improper gap between sensor and speed sensor ring
i will add: change the rear gear fluid
check for presence of the following conditions:
damaged missing or bent teeth
metal chips on speed sensor
open or shorted sensor
improper gap between sensor and speed sensor ring
i will add: change the rear gear fluid
Thanks for the info and suggestions. I took the speed sensor off recently when I was trying to put on the new connector for it, it had a little bit of metal on it I cleaned off. I looked at the ring it reads and it looked fine but I didn't turn the rear wheels to check the entire ring (on the to do list).
I had the speed sensor ring changed many years ago and it didn't fix the problem at that time.
What I found strange was how the speedo jumped a little when the RABS/VSS wasn't even plugged in (which leads me to believe the RABS/VSS is fine).
I'll try and put a washer under the sensor/bolt to increase the distance between it and the ring.
I had a friend change my rear axle seals year or two ago and he said he changed the diff fluid but I'll keep that in mind too.
I seen the wires from the RABS/VSS runs up the drivers side frame rail, I'm going to try and trace it... does anyone know where it runs to? Is any other sensor used to feed the speedo that could be causing noise? (if the RABS wasn't the VSS I was thinking that might be it but I can't find the VSS, I guess because I don't have it)
Elder User
Joined: Dec 2002
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From: South Carolina
I heard somewhere that the new PSOM's were calibrated differently, less sensitive to the signal generated by the tone ring. It might make a difference if you swapped for one of the new calibration PSOM's. I think it has a "3" at 12:00 above the speedo, hidden by the dash bezel until it's removed. The old calibration was a "2". When I replaced my PSOM for a stall condition, it also cured the speedometer waver at 50+ mph.
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Originally Posted by Cheggie
I heard somewhere that the new PSOM's were calibrated differently, less sensitive to the signal generated by the tone ring. It might make a difference if you swapped for one of the new calibration PSOM's. I think it has a "3" at 12:00 above the speedo, hidden by the dash bezel until it's removed. The old calibration was a "2". When I replaced my PSOM for a stall condition, it also cured the speedometer waver at 50+ mph.
)! The instrument cluster I have is an older one from Ebay, I'm fairly certain it would be the older one like my stocker.
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New User
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I had a speedo that was jumpy it ended up being the speedo itself, I grabbed a new clustor from the junk yard plugged it in and it was the end of my jumpy speedo
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Post Fiend
Joined: Mar 2002
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From: Bonita Springs FL
One really important piece of information is what year is your truck? Everyone is assuming you have an electronic speedometer that runs off the VSS, but that was only the case in 92 and newer trucks.
Always check the obvious first.
Always check the obvious first.
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Originally Posted by andym
One really important piece of information is what year is your truck? Everyone is assuming you have an electronic speedometer that runs off the VSS, but that was only the case in 92 and newer trucks.
Always check the obvious first.
Always check the obvious first.
I can't think of anything else to test at this point. Maybe a bad ground somewhere?
Elder User
Joined: Dec 2002
Posts: 559
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From: South Carolina
I got a replacement at dashusa dot com, and it was about $200. They sell the rev3 PSOM, and it works like a champ. Hey - it's cheaper than most car payments! You need to tell them the current mileage and calibration constant, and they'll send it right to you, ready to go. It's not hard to install, and you don't have to pay Ford! It is an exchange part, so you have to send your old unit in upon receipt of the new part.
I really needed it - it was causing a stall because the speedometer was LYING to the pcm and activating the fuel cutoff at 3 mph.
I really needed it - it was causing a stall because the speedometer was LYING to the pcm and activating the fuel cutoff at 3 mph.
