My Outrageous Speedo Saga

[soundie]

I posted this in General too, hope thats ok with mods..

Help!

Car is a JDM 99 WRX that had factory fitted cruise control, a funny delimiter with a strange switch, a ‘WRX-RA’ ecu, and lots of extras.

The symptoms of the problem were the speedo needle was jumping up to 30ish mph when the car came to a halt, or after engine being switched on. Then the speedo ceased reading speed whilst in motion, and it still jumped around occasionally.

The car goes into limp mode after any high boost, I suppose because the speedo isn’t giving information to the ecu, which is why it needs fixed! Paid up trackday on Saturday so I need to get it fixed v soon

First I tried changing the speedo sensor, no difference. Then changed the speedo binacle, no difference. Then tried a mates ECU: no difference. Now Its in bits at SW Motorsport having changed the delimiter to simpler one, deleted all traces of cruise control, and STILL no difference.

Has anyone ever heard of anything like this?? I’ve tried searches but my keyword choices must be lacking..

Thanks, Any help hugely appreciated!

Chris.

[agent smith]

Is it causing the CEL to come on?

I had a similar problem and it was all due to a speed de limiter, Km to MPH convertor, thingy that I wired into the speed sensor loom. I removed it completely, problem solved.

[soundie]

Yeah thats right, the CEL comes on and the fuel cuts and car enters limpo modo.

I think the original kph converter is deleted, assuming its the same unit as the delimiter, a maplin looking box with a switch on it. THIS was fitted to replace it.

There's every chance the kph converter is somewhere else I suppose.

I presume if the delimiter is deleted, the car won't get to 120mph on Knockhills straight anymore?

Cheers

[johns]

It's definitely something to do with the speedo. For some delimiters there used to be a small geared adaparter which fitted onto the speedo cable from the gearbox I think, which geared down the rotations to the speedo cable.

About 120mph is the top end for a reasonably powerful Impreza on the main straight at Knockhill (standard cars will be about 100 - 105mph actual) and will be faster than most of the Elises and Caterhams. You might have to back off the throttle just a second or so before the braking point so shouldn't impact your enjoyment too much

Hope you get to the bottom of the problem

John

[soundie]

Thanks john me too

It's definitely something to do with the speedo.

do you mean the speedo head/cluster thingy?

Was it not just the older imprezas that had a speedo cable? my cluster only has the 3 green plugs into it..

throttle back? what on earth do you mean?? lol.

[agent smith]

Yeah thats right, the CEL comes on and the fuel cuts and car enters limpo modo.

I think the original kph converter is deleted, assuming its the same unit as the delimiter, a maplin looking box with a switch on it. THIS was fitted to replace it.

There's every chance the kph converter is somewhere else I suppose.

I presume if the delimiter is deleted, the car won't get to 120mph on Knockhills straight anymore?

Cheers

If you get two seperate codes, one relating to the speed sensor, cant remeber the exact numbers, then its the same problem I had. My car is and import version 5 1998, so the speed sensor/cable should be the same type. The thing I fitted then removed after it failed, was a smalled circuit board in heat shrink, with four wires, one wire dosent get used. generally found behind the dash or on the speed sensor cable coming out the gear box. Do your clocks show in Km then?

[agent smith]

If you get two seperate codes, one relating to the speed sensor, cant remeber the exact numbers, then its the same problem I had. My car is and import version 5 1998, so the speed sensor/cable should be the same type. The thing I fitted then removed after it failed, was a smalled circuit board in heat shrink, with four wires, one wire dosent get used. generally found behind the dash or on the speed sensor cable coming out the gear box. Do your clocks show in Km then?

Sorry just noticed the Ebay link,, thats the one,, i went out to see Andy forrest after it failed and he adjusted the limit for me.

[johns]

I can't remember when they moved over to electronic speedo's which are driven by electrical pulses, instead of an actual cable.

If the sensor has been swapped out, then I would check the signals are getting through from the gearbox to the ECU OK.

[soundie]

If you get two seperate codes, one relating to the speed sensor, cant remeber the exact numbers, then its the same problem I had. My car is and import version 5 1998, so the speed sensor/cable should be the same type. The thing I fitted then removed after it failed, was a smalled circuit board in heat shrink, with four wires, one wire dosent get used. generally found behind the dash or on the speed sensor cable coming out the gear box. Do your clocks show in Km then?

The clocks showed in Mph fine before, now after deleting the delimiter and fitting an ebay one similar to what you described (item no 120446038867) it should still read in mph, but needle's dead so don't know. I guess it would read in Kph if I deleted the delimiter too!??!?

so your car reads in kph and is limited to 113mph then, is that correct?

Thanks!

[soundie]

Sorry just noticed the Ebay link,, thats the one,, i went out to see Andy forrest after it failed and he adjusted the limit for me.

ah, haha..

Well, Andy Forrest and Steve Whitson have been conflabbing about it this week and he had no idea what to do.. mind you I'm not sure if a code check has been done yet..

[soundie]

I can't remember when they moved over to electronic speedo's which are driven by electrical pulses, instead of an actual cable.

If the sensor has been swapped out, then I would check the signals are getting through from the gearbox to the ECU OK.

Yea the sensor has been swapped (though who knows if this one works, really)

How would I check that john? ...Or, how would steve check that

[scoobywho]

My skyline did that till I chucked out the KPH convertor

[WUZ]

I've seem this happen on a car I've worked on up here. Issue was solved by replacing the wire the sends the signal from the Gearbox Sender to the ECU as the speed signal goes from Sensor - ECU - Speedo

[soundie]

My skyline did that till I chucked out the KPH convertor

I've seem this happen on a car I've worked on up here. Issue was solved by replacing the wire the sends the signal from the Gearbox Sender to the ECU as the speed signal goes from Sensor - ECU - Speedo

Thanks guys, two approaches I'll get onto now

C.

[ali37]

Had this exact same problem with my 99 STI RA.

I seem to have solved it by running a parallel wire for the signal wire going to the ecu from the speed sensor on the gearbox.

You have 3 wires going to the speed sensor.

+12v

-12v

Signal to ecu

The signal wire came from the speed sensor, through the kph/mph convector then to the ecu.

I have added an extra wire to run in parallel from the convector to the ecu and it seems to have solved the problem.

I assume that the wire must be rubbing somewhere and grounding against the body.

As Wuz states the wiring is sensor - ecu - speedo.

When Andy F was mapping last month he could see the signal from the sensor to the ecu fluctuating and dropping off so knew the problem was not the speedo.

Ali.

Edited September 15, 2010 by ali37

[soundie]

Had this exact same problem with my 99 STI RA.

I seem to have solved it by running a parallel wire for the signal wire going to the ecu from the speed sensor on the gearbox.

You have 3 wires going to the speed sensor.

+12v

-12v

Signal to ecu

The signal wire came from the speed sensor, through the kph/mph convector then to the ecu.

I have added an extra wire to run in parallel from the convector to the ecu and it seems to have solved the problem.

I assume that the wire must be rubbing somewhere and grounding against the body.

As Wuz states the wiring is sensor - ecu - speedo.

When Andy F was mapping last month he could see the signal from the sensor to the ecu fluctuating and dropping off so knew the problem was not the speedo.

Ali.

Excellent, I've just texted this to steve, thank you!!

God I hope this fixes it, and god I hope i make the SIDC day this sat I've missed the last two trackdays and a summers scoobying because of this silly palava

[soundie]

Well, that wasn't it folks. SW bypassed all the kph mph converter / delimiter stuff, added temporary ecu speed signal wire and hardwired power to the sensor, still nothing.

I rang scoobyclinic and straight away the guy (adam - nice man) said its the 'worm drive' in the gearbox, just below the speed sensor. The plastic thread has been ruined or something. So it requires opening up the gearbox and replacing.

doesn't look like the trackday gods are smiling down on me thats for sure.

Cheers,

Chris.

[soundie]

sorry, jumped the gun a bit,

it can't be the worm drive, since the needle jumps around when the car is stationary..

so my appeal for help continues.

got a spark booked for monday morning, i'll maybe get him to put a multimeter across the sensor and drive about, see if there's a signal coming off it. at least that elimitates the worm drive / sensor possibility.

humph.

[sti pretender]

Might be a silly question have you checked the wires into the connector for the ecu and sensor. If a bypass was run it would be tied in after coming out the connectors. If everything has been replaced and Andy and Steve can't see anything i might be something really simple.

Just thinking back to a starting problem that Richie had in his Type R when he had an intermitant starting problem, tried everything to solve the problem (ecu swap, starter, etc) until he found a tiny break in a wire in the connector to the ecu.

Hope you get it sorted.

Robert

[soundie]

Hi Robert,

cheers.. it is very symptomatic of a break in a cable somewhere, I'm not sure exactly where the bypass was tapped in, I would hope it would have been directly into the connection, but certainly worth emphasising your point, thanks.