Stevebyng

I have a "95" WRX 5 door with a mechanical speedo. I have fitted a UK spec mph speedo but still have a speed limiter that cuts in around 115mph. Rumours are that the speed limiter is built into these mechanical speedos. Can anyone confirm this and if so how to remove it?

Freck

Nope, the speed limiter on the Mechanical Speedo cars is I think built into the ECU, and you just have to get it rechipped.

abetts

I have just personally imported a WRX STi ver 3 with mechanical speedo; I suspect the set up is the same as yours. The speed limiter consists of a reed switch in the speedo which supplys a signal to the ECU. Take the instrument cluster out and look at the rear of it. You will see a screw in the back of the speedometer labelled "RSW". Connect that screw with wire to the identical screw which is also in the back of the speedo. Bingo! You have just rendered the speed limiter inoperative by shorting it out.

Alternatively, have your speedometer re-calibrated from kph to mph by a specialist. This will cost you about £100 but it is a far more professional way of doing things than simply changing the face which will leave you with a speedo that only reads to 112 mph and an odometer that reads in kilometers. Re-calibration will give you a speedometer that reads from 0-180 mph, an odometer that is in miles and a speed limiter that will not operate until 180 mph! If you need details of a reliable compafor re-calibration feel free to contact me.

Alan Betts

abetts

By the way, if you think about it, the earlier reply suggesting that the speed limiter is built into the ECU is technically right. It is, however, the reed switch in the speedo which supplies the information to the ECU so if you knock out the reed switch the ECU is non the wiser.

All you have to do to fathom out the speed limiter on any car imported from Japan is fathom out exactly where the signal is coming from and there are only a limited number of possibilities. One alternative I considered, for example, was that an ABS sensor could be used to perform the same function.

The system Subaru have actually chosen to use on my 10/96 WRX STi is surprisingly crude.

Alan Betts

abetts

One further point.

There may be more than one method of restriction but as I have yet to
drive my car at more than 112 mph I don't know for sure.

One thing that is a little bit odd on my car is that the gearbox has
two electrical sensors. You can see them by jacking up the front of
the car and then looking on the near-side of the gearbox. Each has
two wires coming from it. One is bound to be the reversing light
switch. But I can't work out what the other is for given that my car
has no oil gearbox oil temperature guage, gearbox oil pressure guage
or whatever. One possibility is that it monitors the speed of the
gearbox output shaft and when it hits a particular number of RPM it
signals the ECU which implements the speed limiter.

I mention this because on thinking about your position further, I
cannot work out why the speed limiter would still be working in
the absence of a Japanese spec. speedo as the UK speedo has never had
a speed limiter fitted.

I will look into the gearbox sensors at a later date and if I
discover anything I will post it on the BBS.

If you are curious, the reed switch in the speedo is the rectangular
plastic thing with an electrical contact on each end. It is around
two inches long and, if I remember right, it is coloured blue. It
is essentially the same thing you get in burglar alarm window
contacts and works by magnetic fields. I discovered how it worked by
spinning the speedo with a variable speed electric drill in reverse.
The circuit remains complete until around 112 mph, whereupon it goes
open circuit. By connecting the two contacts together you fool the
ECU into thinking that the car never reaches 112 mph.

Pete Croney

Scoobysport sell a gismo that reduces the cable speed by approx 1.6. The speedo then reads 180 mph and you never reach the limiter. Calibration has been telemetry tested and the speedo readout is very accurate.

Stevebyng

Well I finally connected a cable at the back of the speedo to short out the reed switch.
Everything was OK for the first few miles and then the check engine light came on.
By connecting the self diagnostic plugs under the dash i found that the problem was fault code 33 = vehicle speed sensor.
It therefore seems that on my vehicle shorting the reed switch prevented the ECU from receiving the correct vehicle speed reading which put into the limp home mode.
I disconnected the wire and reset the ECU and the check engine light has not come back on yet!
I have two long drives tomorrow and Wednesday so I hope it stays that way!

abetts

I had no problems as a consequence of shorting out the reed switch on my 10/96 STi so I guess there must be some technical differences between my car and your '95 WRX. But in the end I got fed up with a speedo that only read up to 112mph and so I switched to using a reduction gearbox in the speedo cable (from Speedy Cables 0171 226 9228). The cost was just under £100. Now I know when I am doing 130mph, er, on the Autobahn.

abetts

By the way, re. my earlier reply about gearbox sensors. The second gearbox sensor signals whether the car is in neutral or gear.