wiring of a vdo speedo

[Chris Brown]

Hi all I have a problem I hope some one can help I had the cobra on the dyno and it came up with a fault which said the speed sensor to the ecu (standard ecu series 1 au xr8 5lt) was not working, checked my wiring and found that the sensor wire was being used for the speedo and ther was no wire on pin 58 on the ecu, if I rewire to ecu the engine will run up to full revs but I have no speedo if I connect to both the same thing happens the only way I can get speedo to work is only wiring it direct to sensor but engine won't rev out can someone help.
Chris

[sideshow]

the factory speedo gets signal form the gbox then form back of the speedo there is an output speed signal that goes to the ecu
now if yr speedo doesnt have this then the signal might be too weak to run both
but being a square wave it should not loose strength so i think the signal might be slightly wrong

now every time i wire up an au v8 auto well the ecu needs the speed signal so it changes gears took me awhile but i figured if i ran factory speed signal from gbox to ecu it still isnt good i had to run a signal booster to amplify the signal form speed sensor on box to ecu and it fixed the problem

not sure if this will help but it works on all the au autos i have done

this unit will actually take a weak input signal and amplify it and it also has a small led to show u the pulses coming in

i can sell u one and if it doesnt work send it back
u just have to pay for freight or drive car to sydney and i can fix it
or find someone down yr way

[albanycobra]

VDO speedo's will read off anything....Use your g/box sensor for the ECU and
mount a Commodore ABS speed sensor (about $20 from a wrecker) right next to your tailshaft off the diff housing and it will read off the yoke bolts or get some of those cruise control signal weights and strap them to your tailshaft and mount the sensor near that. We mounted ours on the inner front hub and it counts off the old ABS ring.

There are lots of ways to mount a speed sensor and many types you can use.

Another idea is to use an after market Cruise control speed sensor that piggy backs manually straight off the g/box sensor, you just remove your existing speed sensor push the after market one in and fit a small drive shaft bewteen the original sensor and you have 2 seperate speed sensors driving off the gearbox. I used this type of set-up in my clubman.



Picture is for display only and not exactly what I used but you can get an idea of what I'm talking about.

[Ron61]

I don't know anything about your Cobra and the transmission, but I ran all VDO gages when I had mine, and I just used 3 wired for the speedometer. I had a Hall Effect Sensor that went in where you would put the gear on a gear drive transmission and it had a power wire, a ground wire and a sensor wire, all of which connected to terminals on the back of the speedometer. I had it for about 13 years and never a problem, even when I would change tire sizes or something, all I had to do was push the button until is said automatic, drive the car a mile and stop and push the button again and it would automatically set the speedometer for the change. I know it read right as I would then take it over to the CHP and ask them to go with me and we went to a deserted stretch of highway and they would use the radar to check my speed at 60,70,80, and 90. Always right on.

Ron

[Chris Brown]

Thanks sideshow I was thinking down that line but wasn't sure.

Thanks Dave if I don't have any luck with adding a extra positive I will call.

Thanks Ron I have had it wired like that for the past 4 years but its only now I have traced why it wont rev out.

Thanks again I am going to have another play I will let you know how it goes
Cheers Chris

[Merv and Sharon]

Geez Ron, sounds like the CHP were committing a felony there! Over 65mph?

Merv

[Ron61]

Merv,

It helps that we are in a rather scattered area and there are some old unused highways around here that were replaced when I-5 was built. Plus a couple of the CHP then I knew personally, and they knew I would never drive like that on the highway. I just wanted to test it out for the track to be sure it and the tach were on with each other. But that would never happen again here.

Ron

[sideshow]

hey try this at yr own risk

what i do on some toyota ecus is bridge the speed signal input wire on the ecu into one of the injector trigger wires
this gives a good enough pulse to the speedo wire on the ecu and allows some toyota ecus to have a 8500 rev limit and not a 7500 if there is no speed signal