Mysterious black box (not ECU).

[Snaek]

Hi,

does any one know what this is and what does it do, it is connected into the dash wiring loom (1995 pre facelift).

Mel.

[SILICONEKID346HP]

Snaek said:

Hi,

does any one know what this is and what does it do, it is connected into the dash wiring loom (1995 pre facelift).

Mel.

Blitz will answer that one .. looks like another fuel chip .

[blitzracing]

Thats the infamous speedo calibration unit that produces a fixed speed signal to the ECU once the car is moving.

[Mr Supercharged]

Where does that live in the car? Under the dash? Presumably it can be thrown away when you go aftermarket ECU or does it also convert the signal from the tooth counting sensor on the half shaft and output to the speedo? I like the idea of de-cluttering if possible hence the questions....

[SILICONEKID346HP]

Mr Supercharged said:

Where does that live in the car? Under the dash? Presumably it can be thrown away when you go aftermarket ECU or does it also convert the signal from the tooth counting sensor on the half shaft and output to the speedo? I like the idea of de-cluttering if possible hence the questions....

I want to get rid of that too.

[blitzracing]

It wont be needed for the aftermarket ECU. Its a very simple unit, and does not appear to have an output to the speedo as such- but please simply try unplugging it and see if the speedo still works.

[NZ fan]

My 95 had this under the dash. It is obviously a buzzer where as yours dosen't appear to have the buzzer part but those two chips (14 leg and 8 leg) do look similar. Mine was tucked away in the dash to the right of the radio behind the light switches. It just started buzzing continually so I removed it. Figured it might have been something to do with the original alarm or maybe a headlight reminder but I understand they don't have these? Anyway nothing has stopped working as a result.

[Snaek]

Thanks guys,

There is one wire to the speedo and two others that vanish into the loom which I have not traced back yet.
I am fitting a megasquirt and if this is reliant on the Lucas ecu how will the speedo work when using a megasquirt ?

Mel.

[Mr Supercharged]

Snaek said:

Thanks guys,

There is one wire to the speedo and two others that vanish into the loom which I have not traced back yet.
I am fitting a megasquirt and if this is reliant on the Lucas ecu how will the speedo work when using a megasquirt ?

Mel.

The speedo signal is generated from the sensor on the half shaft counting teeth on the wheel (offside half shaft from memory), this signal I think is what the speedo sees directly and I suspect that box is what is generating a compatible road speed signal from the pulsed sensor to go the the Lucas 14CUX only. The 14CUX likes to know what the road speed is so that below, a certain speed (10mph or something similar) uses this as a trigger to go into idle control mode if other triggers conditions are also met. It is quite a clever ECU, is just a shame it didn't control ignition and wasn't readily re-mappable by the majority.

[Snaek]

Thanks, I will up it to the test further down the line.

Mel.

[blitzracing]

I would suspect the feed to the speedo, is infact from the speedo. The box looks for a sequence of pulses corresponding to about 3mph, and then fires a fixed speed signal at the ECU of between 30 and 50 mph. The ECU needs a signal to know if the car is moving to alter the stepper control, or in the case of a 4x4 if its gong too fast for those off road tyres. TVR frigged it with a fixed speed signal, thats good enough most of the time.

[Snaek]

Thanks Blitz,

I understand now from yours and others inputs how it is supposed to work and will check it out.

Mel.