tachometer and speedometer incorrect readings

[spaceistheplace]

just helped a friend purchase a 1999 sl1, automatic, about 93k miles. runs and drives great, but noticed during the test drive that the tachometer reads way high, like 1000 rmp higher than normal. i own 3 of my own saturns and drive them regularly, so i feel pretty confident that the new car is idling normally (7-800 rpm), and is shifting smoothly though all the gears (at 2-2500 rpm) but the tach reads about 1000 rpm higher than that. we also realized that the speedometer was reading about 10 mph LOWER than actual speed. have not tried hooking up a scan tool yet to see what the pcm thinks is happening...

the car seems pretty much stock, except for the seller had installed a remote start system. also it has 185/70r14 tires on it (is that enough to cause a 10mph difference between speedo and actual speed???). has the 110 mph speedo and single cam engine, but it does look like someone has been into the cluster (trip reset button is missing and there is a small crack in the glass.) odometer and other gauges appear to be working normally.

idk if its relevant, but it has abs and traction control, and the traction control is not working (the button lights up when you hold it, but does not stay on).

the car is super driveable as-is, but i am curious as to what could be causing the cluster issues. let me know if there is any other info i can provide. thanks

[Signmaster]

More info is good.

Does the tach seem to rise and climb normally? Has the speed been check vs GPS at least?

The small tire size changes can be calculated using on online calc quickly, but aren't going to have much impact at that size.

Revs vs true speed (in forth gear and locked up) and GPS vs indicated speed would both be things that can be checked quickly and easily.

[spaceistheplace]

well, just looked at the car again, and realized i overlooked the most obvious answer: the needle on the tach rests at around 1500 with the car off! duh! i guess we started it using the remote start, so it was already running when i drove it lol

do these tachs ever get stuck like this? or probably the needle was removed and installed in the wrong position?

thanks signmaster, will compare speedo reading with gps speed. looks like that needle may be a little off the mark too.

[fetchitfido]

It's probably a sign of the cluster failing, which is annoying for '98-'99 as the odometer is digital and locked to that particular cluster.

On the off chance it's from someone screwing with it, you can screw with it again. Take the cluster out, pull the clear overlay off and use a fork to carefully pull the needle(s) off then reinstall them at 0.

If the cluster backing color isn't black or silver-ish with "homecoming" written on it then someone could have put custom backing overlays on it which could be making the needle stick in a certain spot but then it'd read 100% normal away from said spot.

[Signmaster]

Originally Posted by fetchitfido

It's probably a sign of the cluster failing, which is annoying for '98-'99 as the odometer is digital and locked to that particular cluster.

On the off chance it's from someone screwing with it, you can screw with it again. Take the cluster out, pull the clear overlay off and use a fork to carefully pull the needle(s) off then reinstall them at 0.

If the cluster backing color isn't black or silver-ish with "homecoming" written on it then someone could have put custom backing overlays on it which could be making the needle stick in a certain spot but then it'd read 100% normal away from said spot.

Hopefully this would be the case. Much easier to fix if it's just been screwed up by someone that doesn't know what they are doing with simple mods.

[MiSaturn]

I inadvertently did something similar when replacing my odometer gear a couple of months ago.

I must of bumped the needle when working on it, and now it reads 6mph faster than it should regardless of how fast you're going (20=26, 35=41, 65=71mph).

A real PIA, but I figured I'd live with it until I had a good reason to open up the dash again.