Incorrect Veichle speed

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Hi!

I have searched this topic without any luck..

My car is a '98 Gs-t.

When I drive, it always shows 20km/h higher speed than actual speed on my Garmin GPS.
At 50km/h I have 30km/h. At 100km/h i have 80km/h. At 200km/h I would also have EXACTLY 20km/h incorrect reading.

Previous owner told me that after installing blue instrument lightning, it was at 200km/h at any speed.

After an electrician used some time on it, it shows now 20km/h higher than actual speed.

Thinking of my milage running that much faster than actual, and that it shows incorrect value, I want to fix this!


Do anyone have an idea what my problem can be here?


Any help will do good!


Thanks,

John

 

[DSM1G90]

Do this simple trick: Being in Km..(do any of your highways over there have Km markers on the side of the roads?) set your trip odometer back to zero the instant you pass a Km marker. When you meet the next Km marker, your odometer should read, or very close to, "1km" when you pass that marker.

OR, another one: If you have a watch on with a chronograph on it, set the chronograph to zero and have your speed at 97kmph, when you hit a marker, start the chronograph and a minute should pass when you hit the next marker at this constant speed of 97kmph.

Sadly, GPS units aren't that all correct and accurate at times... just more common methods to figure out distances..


Also, if you have incorrect tire sizes from the stock 205/55R16 size, this could throw off the speedo by some degree.

good luck - DSM

 

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Do this simple trick: Being in Km..(do any of your highways over there have Km markers on the side of the roads?) set your trip odometer back to zero the instant you pass a Km marker. When you meet the next Km marker, your odometer should read, or very close to, "1km" when you pass that marker.

OR, another one: If you have a watch on with a chronograph on it, set the chronograph to zero and have your speed at 97kmph, when you hit a marker, start the chronograph and a minute should pass when you hit the next marker at this constant speed of 97kmph.

Sadly, GPS units aren't that all correct and accurate at times... just more common methods to figure out distances..


Also, if you have incorrect tire sizes from the stock 205/55R16 size, this could throw off the speedo by some degree.

good luck - DSM

My tires are 225/40R18. Should be somewhat correct?

I have actually run past a speed-test-device by the road. My speedometer was at 80kmph, and the speed-test-board showed 59kmph.

No wonder I was a major queue builder before I knew that..

Any other stuff that can be wrong?

Thanks for your input!


John

 

[TunaTalon]

The stock tires on a 1998 turbo front driver (Talon TSI) were 205/55/HR16
Those tires make about 840 revs/mile (tirerack).
Your current 225/40/18 tires make about 833 revs/mile (tirerack).

Your tires should be within 1 percent of stock. Look elsewhere.

 

[Join]

Hmm..

Is there a difference in the AWD& FWD sensors? Different gears or so? I do not know if it is the stock sensor installed.

 

[voodoogsx]

I have the same prob on my car. It shows 10mph over based on gps(pretty reliable thus far) as well as traking other people when I first noticed the anomoly. Last verification was the cop that pulled me over... hmmm...yeah, I was going 85 all right....

The previous owner had pulled the consol off and added some backlight or something...not to mention some fuzzy math going on with my odo....

 

[Join]

I have the same prob on my car. It shows 10mph over based on gps(pretty reliable thus far) as well as traking other people when I first noticed the anomoly. Last verification was the cop that pulled me over... hmmm...yeah, I was going 85 all right....

The previous owner had pulled the consol off and added some backlight or something...not to mention some fuzzy math going on with my odo....

Then we have at least one thing in common. The added backlight made by previous owner!

Can that be the reason?

What type of signal do the speed sensor provide? a count signal, or a raising/lowering voltage?
Can I install a variable resistance/amplifier to adjust the speedometer?

 

[knochgoon24]

Then we have at least one thing in common. The added backlight made by previous owner!

Can that be the reason?

What type of signal do the speed sensor provide? a count signal, or a raising/lowering voltage?
Can I install a variable resistance/amplifier to adjust the speedometer?

I don't know if that would even be legal. Even where you live.

 

[luv2rallye]

What type of signal do the speed sensor provide? a count signal, or a raising/lowering voltage?
Can I install a variable resistance/amplifier to adjust the speedometer?

The vehicle speed sensor (VSS) generates 4 pulses per rev. No you cannot install a variable resistance/amplifier to it. Does this backlighting generate high voltage and/or AC signals (aka: electrical noise to other instruments)? It may be interference from it that is affecting the VSS. Disconnect this backlighting to see. If it is you could try shielding the VSS wiring or adding a small capacitor on it to filter out higher frequency noise. Depending on how strong and the frequency of the noise this may or may not work. If that doesn't work put the stock backlighting back in.

 

[96mitsugsx]

The VSS is the same for the GST and GSX. I just fixed a GST 2 months ago with the same problem. It was the instrument cluster. What we did is that we transfered my cluster to his car. That's how we found out that it was the cluster.

 

[4Motion4g63]

I seen a 2g with a indiglow cluster that was strobing it was so screwed up and that guy was complaining that the spedo was off also...

 

[DSM1G90]

The added backlight made by previous owner!

Did he get the needle back to mechanical zero after this added backlight kit..makes you wonder. Plus, once the needle get's pulled off it's shaft, it may not be secured on the shaft and that could cause some drifting by the needle on the shaft.

Also, the lightening mechanism could have dire effect on the rotating magnet/drum assembly in the speedo ass'y itself.

Another simple test: Is the speedo needle secure on it's shaft? Also, where does the needle rest when stopped?

Is the speed errors throughout the whole kilometer spectrum, or just in a certain area of the gauge?

I had one car where the needle shaft would rest on the stop rest peg, but the shaft would still want to twist the needle, thus the needle had rotated on the shaft giving me incorrect speedo readings. I opened up the cluster, took off the needle and readjusted the needle to the mechanism stop and I got my correct readings again.

Also, would your speedo cable be having fits of sorts - by twisting and flexing inside the sheath? Also, if it's dry, you can also clean out the cable with some sort of parts cleaner and relube the square cable itself.

Good luck - DSM

 

[Join]

The vehicle speed sensor (VSS) generates 4 pulses per rev. No you cannot install a variable resistance/amplifier to it. Does this backlighting generate high voltage and/or AC signals (aka: electrical noise to other instruments)? It may be interference from it that is affecting the VSS. Disconnect this backlighting to see. If it is you could try shielding the VSS wiring or adding a small capacitor on it to filter out higher frequency noise. Depending on how strong and the frequency of the noise this may or may not work. If that doesn't work put the stock backlighting back in.

Perfect answer to my question! Ok, then that will not work..Was not my work..

Thanks

 

[Join]

The VSS is the same for the GST and GSX. I just fixed a GST 2 months ago with the same problem. It was the instrument cluster. What we did is that we transfered my cluster to his car. That's how we found out that it was the cluster.

So maby I should try to get ahold of a new cluster? Where can I find a good one?

How much time did you spend changing them?


John

 

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Anyone?

 

[96mitsugsx]

The owner of the car found one on ebay for $80. You might wanna try the classified section here on Tuners. Changing it was really easy. About 15 minutes to take it in and out of the car.

 

[Join]

Hi!

I just want to let you know what was wrong! >The someone who installed the super-glow backlightning stuff, have not put it correct together after, leaving the speedometer needle in wrong position, reading EXACTLY 20km/h higher than actual speed. My fuel-gauge also never read below 1/4tank, from the same reason.

Got a "new" gauge cluster from a '99 now, and everything is working great!