Hope this will get the right audience... Electronics & Scooby's anyone?!?

I am involved with motorsport electronics (mainly kitcars/single seater racers). I have designed a dash system that can log performance etc that I am trying to get to work with the scooby's standard ECU outputs.
(www.customautotech.co.uk if you're interested).

I've added two pickups from my cars ECU that I thought were the RPM and the speedo.
Well - they are. Sort of.
The RPM is perfect, and I thought the vehicle speed pickup was too. But in use the dash refuses to read a speed of over 91mph. I have scoped up the feed from the ECU on the move and this simply stops getting faster at 91mph - it just holds that frequency.

Can anyone shed any light on the ECU used in a P1 and what signal I am looking at! Would it be the speed signal for a volume sensitive stereo?

I used the 2.0l turbo diagram from here:
http://www.ravensblade-impreza.com/modifications/misc/wiring/wiringdiagram.pdf

Cheers,
Marc

It may be that the P1 is based on the STI which is a Jap spec car, which is limited to 110mph, by Jap law. The P1 is fitted with an electronic gadget that removes the speed limiter ( as far as I know ), by giving the ecu a false speed signal. Possibly you have tapped into this after the de-limiter.
I would locate the speed signal closer to the gearbox, for an accurate signal, if you cannot locate the de-limiter.

Marc,

On your site you have a pic titled "piggyback module with Prodrive on" . That is the kph-mph converter.

Thanks for the info guys.

My first guess was the kph-mph thing, but I wasn't too sure why it would be 91mph rather than 110mph?

I'll take it apart again at the w/e and see whether the kph-mph device feeds in on the same wire (and I will try the other wires).

Cheers,
marc

It may limit to 91, to ensure it never comes close enough to 110 trigger the limiter.

Marc - Can you help me, see here

Variable gear change indicator circuit

The black box does not actually alter the limiter. The ecu looks for 180 (its expecting kph) for the cut.

The converter should have four wires, earth, 12v, kph input and mph output. I have a v5 STI which uses the same converter, but alas without the Prodrive sticker ;)

FAO Nezz10

The RPM signal coming from the ECU (which I assume is the same as your HUD signal) is a 0 to 12V (really 13.8V) squarewave. I measured its frequency when I was setting up my dash.

At 1300RPM the time-period was 23ms, giving 43.5Hz. In a wasted spark system like this you would expect engine RPM to be 30x the frequency. This checks out (43.5Hz x 30 = 1305RPM).
Hope that helps.

Matthew: Cheers for the info. Want me to photocopy you my sticker? ;-)

Marc

SORTED.

Basically the little black box interfaces between the speedo sensor and the ECU as we knew. However it doesn't appear to do what I expected.

I was taking the output AFTER the box i.e. what the ECU sees. WRONG.
______
speedo sensor sig ---->| BOX |---> to ECU ---> to Dash
-------

I took it before the box and the thing just started working. Took it to 125 or so anyway.

What is odd is that I was expecting to have to recalibrate my dash as I expected to now be measuring kph. Except it is quite clearly still matching mph.

The box is thus a speed limiter for the ecu. 91mph sounds real close to the 180mph / 2 someone else mentioned on here.

So in summary - take the feed BEFORE the black box and you will get a full range speedo signal. It is 0-5V and basically operates at the gearbox output/propshaft. You get 1 pulse per prop revolution.

Cheers,
Marc