Cause of my Speedo Needle dropping to zero ?

[macspring]

On my S2 Avant, just wondering what the cause of my speedo needle dropping to zero. It used to happen when I turned on the HID headlights, and then the needl;e goes back to the relevant road speed, and periodically it dies it again during the time the HIDs are lit.

More recently it started to do this during the daytime when the headlights are not on.

Does is need an extra earth connection to be made somewhere ?

Any assitance would be welcome.

Thanks.

[tellas]

renew your hid unit .

[irishs2]

If the odometer stays going, it could be just bad contacts, if the odometer stops it might be the speed sensor on the gearbox.
Apparently it could also be voltage reg for the speedo

http://www.s2forum.com/forum/showthread.php?t=7718&page=3

[mcandmar]

Sounds like dirty contacts to me, if there was an issue with the actual speed sensor i imagine the ECU would chuck its toys out of the pram in protest.

[Colesy]

I've had this happen maybe 3 times in 4 years, I haven't done much investigating as it's so intermittient but would be interested to know what was causing it too.

[John B]

First port of call has to be the speed sensor on the gearbox.

Good clean of contacts on both sides and make sure it is pushed home so that the wire clip locks properly.

[johne]

Sounds like dirty contacts to me, if there was an issue with the actual speed sensor i imagine the ECU would chuck its toys out of the pram in protest.

Dirty contacts I agree with, specifically the long interconnection pins inside the instrument cluster that connect the circuit boards together. As for the ECU, I don't know what - if anything - the ECU does with the speed input but it certainly doesn't care in any obvious way if the speed signal is missing.

John

[johne]

Apparently it could also be voltage reg for the speedo

http://www.s2forum.com/forum/showthr...?t=7718&page=3

There is no voltage reg for the speedo. The voltage regulator on the back of the instrument cluster runs the fuel and coolant temperature gauges only.

John

[macspring]

Further update.

I think it is related to a faulty relay number 208 in grey in the main fuse board under the bonnet at the scuttle.

The car now feels strangled at wot after 4k, which I think is not enough voltage at the 044 fuel pump caused by this faulty relay. (Fuel filter is fresh).

While checking stuff, I found that this relay's pins were very rusty, especially the big power pin, while I filed it "clean" with a small rasp file, however the female pins that it goes into maybe electrically "dirty"?

Going to see if I have a spare 208 relay, and if not, or that doesn't work going to try relaying the fuel pump direct to the nearby battery, (Avant), to ensure the fuel pump can get enough volts on wot.

Will post up results in the next few days.

Thanks for all comments so far.

[mcandmar]

Dirty contacts I agree with, specifically the long interconnection pins inside the instrument cluster that connect the circuit boards together. As for the ECU, I don't know what - if anything - the ECU does with the speed input but it certainly doesn't care in any obvious way if the speed signal is missing.

John

Interesting, no idea what it needs it for either, i assume for some load calculations of something. I have noticed over the years there is something with idle speed regulation, always seems to idle slightly quicker when the car is moving, and settle down when you stop.

[LSG]

My speedo has stoped working now and then just giving the dash a thump worked once or twice. I removed the self under the speedo so i could get my hand up to the wiring and made sure that everthing was pushed together. This seams to have sorted it out so wasn,t to painfull in my case. I hope your,s is an easy fix to . Good luck.

[mcandmar]

Further update.

I think it is related to a faulty relay number 208 in grey in the main fuse board under the bonnet at the scuttle.

The car now feels strangled at wot after 4k, which I think is not enough voltage at the 044 fuel pump caused by this faulty relay. (Fuel filter is fresh).

While checking stuff, I found that this relay's pins were very rusty, especially the big power pin, while I filed it "clean" with a small rasp file, however the female pins that it goes into maybe electrically "dirty"?

Going to see if I have a spare 208 relay, and if not, or that doesn't work going to try relaying the fuel pump direct to the nearby battery, (Avant), to ensure the fuel pump can get enough volts on wot.

Will post up results in the next few days.

Thanks for all comments so far.

Any chance the fuse box cover has been leaking? If you do have corrosion and bad contacts it could mess up supply voltages to engines sensors, maf etc which will odd things.

[mcandmar]

My speedo has stoped working now and then just giving the dash a thump worked once or twice. I removed the self under the speedo so i could get my hand up to the wiring and made sure that everthing was pushed together. This seams to have sorted it out so wasn,t to painfull in my case. I hope your,s is an easy fix to . Good luck.

Thats a sign of the dirty contact pins on the back of the cluster. I thought i put together a thread on how to dismantle and clean it years ago but cant find it

[Error404]

I am sure if the speedo is not receiving a signal from the gearbox sensor, there is a good chance the ECU isn't receiving it either.
IIRC it uses the speed sensor value with TPS value to calculate load so that will certainly have an effect on running?

[macspring]

Further update.

Not more inforamtive I'm afraid, just as confusing it not worse.

Measured the voltage at the fuel pump, and it is 7 volts. so wired up a swtched positive supply from the battery, and went for a drive. It now will go past 4k rpm and onwards to 7k rpm, but still is reluctant to go past say 4k rpm, the speedo drops from it's indicated speed as one goes wot from say cruising at 4k rpm in say fifth or sixth. Like as if there is enough electrical power to go around, Is it a bad or ineffective earth issue?

Where are the various earths that deal with the engine and the instrument cluster ?

I have a spare speed sensor to swop out of the gearbox, and will also check the condition of it's connector plug and its's adjacent section of wiring.

Bit of a pain in rear, as the urS6 revs to the limiter no problem. Just want this car to be able to do the same, with it's much fresher engine.

Checked the spark plugs for tightness, the rubber boots are very fresh, I have the urS6 POS units to swop in to make sure it is not not them.

Is it a permanent + power to the fuel pump, with a switched - earth, or the other way around ?

Will post up what I find when I've relayed the fuel pump and swopped in the spare, known to be working POS.

Any suggestions most welcome.

Thanks.