Hi guys.

new to the forum and have just recently done an engine and trans conversion in my mercedes using an au falcon motor and auto trans.

i used the j3 chip to bypass the ford security on the ecu and the engine is running pretty good. but the issue that im now having is getting a signal from the speed transducer on the trans. i have tried 3 sensors. the original one i got with the trans, one out of a friends running au and finally a brand new one. im not exactly sure how to connect the sensor up. looking at a workshop manual i have it shows the black/green wire is ground, red and white wires are the vehicle speed sensor inputs to the cluster. the cluster then has an output to the ecu/pcm to control auto.

i have read somewhere online and have know idea if its true. that the cluster puts out a reference voltage of 8.2v to the speed transducer and then the other wire is signal back to the cluster. then output from the cluster to the ecu/pcm.

does anyone know if there is a way i can make the speed sensor work?
anyone have a wiring diagram for the for the speed sensor?

any advice would be greatly appreciated!!

regards, Loren

Howdy - good project . ive got one in an e36 bmw.

The speedo Transducer needs 8.2v for power. you can do that using a zener, or you can get an 8v Regulator (LM8508 I think) and a few capacitors and get the voltage fairly easily.

You also need to tie the Transducer output to 12v (from memory) using a resistor. The transducer switches the output to ground, and the ECU doesnt have any pullups. I cant remember the exact value of the pullup - but 1kohm sounds familiar. That holds the transducer output at 12v, except when its "outputting" a pulse.

Once you have a pullup on the output, it can be connected directly to the Speedo Input on the EEC. On an AU, the Dash Cluster provides the Power for the VSS Sensor, as well as buffering the output before providing VSS direct to the Speedo, as well as VSS output for Trip Meter and ECU

Sorry - I dont have the pin numbers or anything here with me.

Nigel

Hi Nigel

thanks for the info!! it has been a very long and painfull project but it should be worth it in the end.

jaycar has the voltage regulator but i dont know what size capacitor i need to use.

do you know what size capacitors i should need?
would a 10 watt 1kohm resistor be sufficient?
do you know which wires are signal input, output and ground on the transducer?

thanks again, Loren

I cheated a little - I got one of these, and swapped the 8v regulator in.
http://www.ebay.com.au/itm/L7809-DC-9V- ... Sw9N1VkCJF

Then I rebuilt it so it was just the size of the regulator - about 3cm by 1cm by 2cm.

For the pull-up resistor - it will go between the VSS Sensor output (not its supply), and 12v. It only needs to be a 1/4 watt resistor - theres no current drawn at all.

As for the transducer - no, I dont know the wire colours. I followed the harness colours in the wiring diagrams

Nigel

Hello,

The IC is an LM7808, it may work fine without any capacitors, they are to " filter " electrical noise. The IC family has been around for decades, you can cheat to change the voltage, but then you dont have all the protection the IC has. For your pull up resistor, 1 K sounds about right. It only needs to be a standard size.

heres a quick diagram
http://www.circuitdiagram.org/12v-8v-co ... lator.html

You probably dont need the heatsink, but Id build it on one anyway - even just a peice of aluminium bar. might even help with mounting.

Id probably run the caps - the EEC is pretty good with noise filtering, but its not perfect

Hello,

You could mount the 7808 on a short bit of Aluminium strap. The ground pin is the center one, and is connected to the mounting Tab. Now I would use small gauge wire to it, and lock them in with a cable tie. Then after insulating the power in and out leads ( before the cable tie ) put some compound all over it. ( potting compound ) which is rubbery and non conductive. I have used non acetic silicon. The vibration in a car will break the legs off the IC if you dont with big wires attached. Hope I'm not telling you what you already know. A Pic would be nice of the engine bay !

thanks heaps for the info Nigel and 96elgli!!

the more info the better! i have no experience with this sort of electronics so hopefully i dont struggle too much to make it work. i will go to jaycar tomorrow and hopefully i can get the bits i need. i will get a pic of the engine bay over the weekend.

thanks again, Loren

Hello,

The IC is a LM7808 It is a series regulator. This means the extra Volts are dissipated as heat. Most modern devices ( power supply ) are switch-mode, where you let a pulse through and smooth it out to become the Voltage you want. As the load changes, the pulse length also changes. This is more efficient, but simple tried and tested is a good thing with a small amount of power.

There are about 3 types of “ package “ you can get a 78 in. TO220 which is the most common, a metal tab and 3 leads. TO3 is a metal oval, same as many large power transistors. There is a low power type, which looks like a transistor. They are rated at 100mA. The other types will handle 1 Amp, and 1.5 with a heatsink. They are short circuit proof, and overload protected. ( in theory ) Max Voltage in is about 35 Volts.

79XX ? This is a Negative Voltage regulator. In circuits you have what we call a 0 Volts, or ground. Now this is different to an earth. If the safety earth and 0 Volts are joined, you have lots of problems with noise in the circuit. A PC supply has + and - Voltages, the – are what the 79xx Regs are for.

I hope this is a bit of an overview to help you understand the device. When you have the Reg, connect it to a 12 Volt 10 Watt globe, and run it for a while. Measure the Voltage you have across the globe, and feel the temp of the Reg. Remove the globe and see how the temp of the device will drop. For what you need, there will be very little load so it will run very cool.

hi,

i have finally wired the transducer up using circuit board i put together. i copied the circuit diagram in the link you shared Nigel. Unfortunately i still cant get the trans to change gears. I think i might have the resistor connected incorrectly. i am getting a signal from the transducer output but it im guessing its incorrect. i have made a diagram of how i connected the resistor.

thanks, loren

 

 

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ford transducer wiring.png [ 4.12 KiB | Viewed 1990 times ]

also a pic of the car and engine bay

thanks, loren

 

 

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windsor mercedes.jpg [ 188.23 KiB | Viewed 277 times ]

Thats a really nice fit.

That looks right (the wiring diagram) - if your getting a signal from the transducer (the ford one, right?) - what else is it driving at the moment.

What pin is it connected to at the ECU?
It should go to Pin 58.

pretty sure its pin 58. i will have to double check that i got it right though its currently not connected to anything else but i will get it to run the speedo as well.

thanks, loren

its definitely pin 58 ive got the signal out put going to. i have a friend who can put his scan tool on it to see if there is any trans related faults. other than that i am out of ideas

Have you put a signal analyser on pin 58? - see if you are getting a square wave input.

Have you also checked to make sure that the gearbox range switch has a valid input?