Hi guys, driving down my street I notice my speedo read 60km/h when I couldn’t have been doing more than 30km/h. I pulled out my GPS and sure enough when I was actually going 80km/h my speedo was reading 120km/h. I then checked the odometer and trip meter against the GPS but both of those were actually climbing at the correct rate.

I stopped the car and then started again and this time the speedo was only reading about 10km/h too high. As I was driving at a constant speed I saw the speedo jump up by 50 km/h for about 10 seconds and then went back down to reading only about 10km/h too high. For the past day it has been consistently reading about 10km to 15 km/h too high at any speed above 50 km/h. Before that speed it seems to be pretty close. Again under any of these circumstances the odometer and trip meter both were rising at the correct rate.

Does the fact that the odometer and trip meter are accurate narrow down what could be wrong? (I.E eliminate the speedo sensor/gear on the tranny and indicates an electrical problem with the speedo itself?)

Thanks for any input.

 

Any help would be appreciated.

Thanks.

 

Have a transmission shop check where your spedo wire connects to your transmission.

 

If the connection was messed up at the tranny wouldn't the odomoter and trip meter also not increase at the correct rate?

 

OK so now it is only reading about 5km high at 100km/h? Maybe if I leave it it will go back to normal. LOL

 

In my car there is a simular problem where the speedo is slow to climb but falls at the correct rate. The odom is correct as well. I am going to switch out the speedo sensor in the next few weeks and see if that helps. I would almost suggest that if the rims and tires are smaller or talled overall that it could be your problem but the mileage is correct so it throws that out the window.

Interesting enough my 05 F250 reads high from the factory, it is 4 off at 40 mph. I learned this by my Diablo programer after thinking that I was going slower than what the speedo read. Plus there is a speed clock on the street by my house that I have checked it against as well. I will tell you it blinks and flashes like hell over 59 mph, I guess that is what I get when it is a 40 mph zone.

 

More than likely the problem is with the electronics of the speedometer.
FD3S speedos are completely electronic. At the driveshaft output of the transmission is a sensor that creates pulses of electricity. The faster the driveshaft turns the faster this sensor creates pulses of electricity. these pulses flow up to the speedo. the speedometer count the pulses to determine how far it has traveled. (I believe it is around 5000 pulses per mile) The speedometer will use the number of pulses over a given period of time to determine how fast the car is going. its almost exactly like a mechanical speedometer setup. Given that your odometer is correctly determining millage, you can safely say those pulses of electricty are getting to the speedometer/odometer gauge cluster. The problem seems to be on the actual circuit board of the speedometer where something is going wrong. changing the speedometer sensor will not help you if your odometer is still correct.

 

That's exactly the info I was looking for. Thanks!! I wonder if there is a resistor or something that is going bad?

Thanks!

 

More than likely, the problem is one of the capacitors or god forbid one of the ICs. go here: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/just-got-done-figuring-out-how-fix-fd-odometer-599220/
Its not your exact problem, but it shows you how to take apart the speedo and has other good info. Your best bet, unless your an electrician/electrical engineer, is to just go through and replace all the capacitors on the speedo board. If you know how to solder thats a plus. If you don't know how to solder you can go to a small computer repair shop, they might know, or ask around a electronic part store or even a car repair shop might help. Your best bet though is to learn how to solder yourself at a community college, look for an electronics lab course. hope this helps

 

Was there ever a solution for this problem?
I have the same fault on mine now. Speedometer showing way too high speed, but tripmeter is ok.

 

Is it reading at speed + a constant (ie always 10mph over the true speed)? Or does it vary, somtimes being 5mph off and sometimes being 20mph off)?

Did you recently play around with the instrument cluster? Remove it etc.? If so then I did figure out how to fix my tach when it was reading incorrectly. You could apply this method to the speedo, but you will need a long empty road and someone driving next to you at constant speed. also, you will need to take your instrument panel apart.

Modified from my tach post:

If it is reading constant and too high ...

"I plugged the cluster in (cluster only no glass or instrument hood) and started the car up and waited until it was warmed up (start driving with someone in another car driving beside you at constant speed). See how much your speedo is off. Then take the speedo needle with your finger and pushed it back to the stop pin. When you let go it should go right back to the incorrect speed. So try pushing it back and lifting it over the stop pin then pushing it back until you feel some resistance. When I let it go this time it should be at a lower speed. Just repeat the process until it reads the same as your buddy in the next car. "

 

No, at lower speeds it is more correct. the higher the speed the more fault.
If i accellerate to over 180km/h where the speedlimiter should kick in there is no limit (i still haven't de-limited the car) . The sensor feeds both ecu and speedometer and as the limiter does not kick in (which is done via ecu) i say the sensor is ok and the fault is in the meter.