Electronic speedo errors, Ver 4+ wrx/sti

[spark_38]

I have noticed in my car and many Version 4 and above wrx and sti that factory speedo's are out by about 10%, if not more.

I have used two different gps units in the car to confirm the error.

For example I am travelling at a true 100km/hr, the Apexi RSM will read 105km/hr and my speedo reads 110-111km/hr (exceeding the 10% tolerance allowable). Having the factory 16" rims and tires on didn't seem to affect the result by much. The error is quite consistent - i.e. at 50km/hr the speedo reads 55-56km/hr. I have been testing this theory for a while now, driving with mates in similar cars: Ver 4-6 wrx, and they all seem to have the consistent error. The Ver 8 and above seemed to fixed the issue (as the error dropped to under 5%).

The older models Ver 3 and below with the cable driven speedo did not seem to have this issue, perhaps a design/programming flaw with the early generation electric speedo change.

I am going to try the Jaycar speedo correction kit mk2. will advise on results...

[WRXER]

I have the same issue in both my wrxs and they are v1 and v2's lol

[kamineko]

can you not set the RSM error correction % ? i had that option on my oldschool apexi RSM

btw pm me if you want the kit cheaper

[Guest lan_killa]

funnliy enough, mine was 10%ish out with the cable cluster and is still 10%ish out with the electronic cluster.... thats according to GPS, but im not overly sure how reliable the speed on the gps is as it seems pretty slow to update

[Joker]

I'm not complaining.. you may find every car on the road is thinking they are doing the same speed as you

they sure would be complaining if they were getting tickets all the time just for 'doing 105'

and those roadside "your speed is : " things are 2km slower than my Speed meter which like yours tells me 105 when Factory says 110

[Guest]

both my V4s have been out quite badly too,

[Shale]

Curious; my ver4 Impreza is bang on. 1km/h out at best with those 'your speed is' things.

The Legacy, however... she is convinced that going down the road at 50-55km/h should read as 70 or higher. And doing the same speed as most on the motorway (NOT the goons in the 'fast lane') reads 120!

So opposite problem to OP on my driveway ;D

[spark_38]

In a way it's a good thing, keeps the speeding tickets down - none so far in the coupe...

[Guest SPANKU]

my is the same but only over 100km/h.

on the BMW the other hand is 100% accurate ( of corse )

[spark_38]

yeah the bmw and the like are generally more accurate, i tested the same gps in a nz new corolla and it was within 2km... at 100km/hr the corolla speedo was at 102km/hr - so the gps units are accurate, the newer uniden ones do update more frequently

a ~10% error at 50km probably goes un-noticed as at that speed, only out by 4km or so...but it is a consistent error regardless of the speed

[G-unit]

mine going by the "your speed is" box on side road is always about 4-6ks higher then im going so at 100k on my speedo im really doing 95ish

[spark_38]

 G-unit said:

mine going by the "your speed is" box on side road is always about 4-6ks higher then im going so at 100k on my speedo im really doing 95ish

subaru are designed to read about 5km or so below the speedo reading, electronic ones anyway...not sure about the cable driven ones

it's when it reads 10km+ below it gets annoying...

started on my jaycar kit last night - got the resistors and capacitors on

[Guest keltik]

Mine has a 10% error in it. As i had to set the Jaycar kit to its upper limit of -99% correction to allow for the speed sensor differences, i still have the 10% error found in the gauge cluster. Quite annoying as to correct it i would have to buy and build ANOTHER jaycar kit

[Joker]

does that jaycar thingy use the hand controller? I dont think mine works (or I broke it)

[Guest keltik]

Nope has a couple of dials on it which you use to set it up

[spark_38]

Finally got it in, i used the 'speed +' wire in my cluster (there are two additional wires 'speed -' and 'speed out' to the ecu). i disconnected the screw at the speed + and that seemed to kill the needle so i went with it.

my rsm is wired to the speed out wire at the ecu end which explains the 5km difference... such thin wires must have quite a voltage drop, esp with the low level signal the wire is carrying

it automatically calibrates (detailed in the manual), and i set it to 10%, seems accurate to the gps up to 50-60 km/hr. i may take for a spin on the highway later on. but all looks good, and i'm well stoked at the $60 or so for the kit

[Guest keltik]

Hey spark, the speed signal is a pule width signal rather than voltage so the thin wires dont pose a problem. The speedo error appears to be in the sensor drive/gauge cluster itself as the cluster is run directly from the sensor rather than from the ecu's output.

[spark_38]

 keltik said:

Hey spark, the speed signal is a pule width signal rather than voltage so the thin wires dont pose a problem. The speedo error appears to be in the sensor drive/gauge cluster itself as the cluster is run directly from the sensor rather than from the ecu's output.

Yeah i figured that, the ECU speed wire is actually an output from the gauge cluster to an input to the ECU. The - and + speed signal must be pulse width, I didn't have my scopemeter handy at the time otherwise could have tested it before and after

Just took it for a drive on the open road, and speedo is now within 1% so really close. The RSM takes the signal at the ECU end is reading about 2-3% below the speedo, so there must still be a slight error from speed signal into the gauge cluster and output...ah well i'll just re-route the RSM wire into the output from the speedo correction kit