Incorrect speedometer reading

[quickster]

Hows it going folks. I'm not new to this site- I was on years ago but have been inactive. Here's my problem. My speedometer is reading too high. I have checked it against my gps. Anywhere from 3 to 15mph. From a stop it will shoot up quickly then level out. After driving a while it gets close to where it should be, but never right. It is cable driven, and I have replaced the vss on the trans tail already.The gear in the trans is fine. Problem is the trans shifts up way too soon. It thinks I'm going fast and shift's accordingly. Going uphill has become a problem-the trans shifts to 3rd or 4th too soon and I have to kick it down with the accelerator. Anyone ever have this problem? Thanks in advance

 

[Bashby]

Is this on your 1990 idi with anE4OD?

 

[quickster]

Sorry I should have mentioned that. Yes it is. Cable driven.

 

[ironworker40]

I'm not familiar with the e 40d but If its cable driven then it drives off a gear in the trans correct? VSS electronic vehicle speed sensor for the computer that runs the trans. If so it has nothing to do with speedometer that is cable driven. If this is the case then I would suspect a cable that needs lube or the speedometer itself is bad. I would pull the instrument cluster. disconnect the speedometer and lube cable with cable lube. Then I would spin speedometer with a drill and see how it acts. Lastly I would pull the gear out of the trans and check that. Thats only if it is cable driven. As far as shifting someone else will have to chime in. Speedo bouncing should have nothing to do with trans shifting if its cable driven. Now if it is electronic driven off the vss then I couldn't say.

 

[OLDBULL8]

Yes, the speedometer is driven off the tranny with a cable drive, but also on the trans end is a transmitter called the VSS (Variable Speed Sensor) they do go bad, or the connection plug there gets corroded, if your speedometer is jumping around, the cable needs lubed. That VSS signal goes to the EEC IV along with the Tach signal and the FIPL voltage setting. FIPL/TPS voltage setting at idle speed is .92 to 1.02, then increase smoothly up to 4.5 at WOT. Voltage setting is with KOEO on the center wire of the FIPL/TPS.

 

[quickster]

The cable attaches to the vss, which has a gear attached on the end of that. The gear is good on the vss, and good on the trans. You would have to pull the tail off the trans to pull the gear- it looks good thru the hole so good for me. Thing is, the cable doesn't jump; it's smooth. When I pulled it off, I spun the cable easily in my fingers. As for pulling the cluster, I did that over the weekend. Came about 2 in out, the I realized I have to disconnect at the trans and pull the housing up thru the floor to get slack. After I screamed, I got a little look behind- it looks like a sealed unit. I could be wrong, but that's all I could see. I read on another site that there is a magnet-sensor thing in back of the speedo. I'm not sure on that. If the cable was bad, wouldn't it jump and read low, not high? The only thing left to try is a new cable. Cheapest and easiest. Maybe someone else will chime in. Thanks Panhead? Nice! Where you, sussex co?

 

[quickster]

re

Oldbull,I replaced the vss a month ago. I spun the cable and no binding. The speedo doesn't jump around, so it isn't making sense to me. Do you know if the cable pulls right out of the housing, or is attached in the speedo? Thanks

 

[79jasper]

The cable is attached to the back off the cluster.
There's a little release in there.
Takes small hands to get in there.

How do the changes in readings correspond to changes in temperature?


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[quickster]

I thought I was the only one that thought temp had something to do with it. When it's cold like it has been lately it reads high, goes up quick from a dead stop. After driving for a while, it seems closer to speed but still off. I was thinking if the cable was gummed up, and being real cold it would read lower. And after it warms up, it would get normal. But that's not the case.
If I pulled the cable out from the bottom, if I can, would it go back in the speedo right? If no problem I'll pull it out and check it.

 

[79jasper]

Pretty sure.


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[riotwarrior]

must unclip speed cable from instrument cluster, then withdraw cable to lubt it then slide it back in.

Since the speedo is a mechanical driven one temp should have no effct unless gear is slippi g in trans or on end of cable...

now the speedo it self could be at fault as its NOT directly driven from cable, just the odometer is...the speedo is driven via inducatnce IIRC....CABLE SPINS A MAGNET jmparting a foce on needle actuator...or something co.plex ljke that lol

 

[quickster]

That is correct about the magnet. The gears on the vss and trans output shaft are perfect, and the cable spins freely. When cold it always registers high speed which leads me to believe that the magnets are the problem. The warmer the cab and outside temp, plus longer driving time bring the speedo down to where it should be.