Tacho???

[AntonyJ]

What drives the tacho? I guess it's somewhere from the ignition circuit ?

Just thinking ahead...

[spend]

The same pulse from the coil that tells the 14CUX how fast the engine is spinning (w/b wire IIRC).

Guessing you are changing the sparking :
You need a way of simulating the 4pulses/rev, whether from the ecu or out the coil packs... otherwise the speedo can be changed (ETB have a clever internal dip switch version IIRC)

[chrispitman]

If your fitting an emerald give them a call as they have a little box to drive the tacho, easy to fit and works perfectly. The tacho signal comes direct from the ecu.

[lwt]

The tacho gets a pulse from the coil as the field collapses. Its called a 'back emf' and can peak at 300v (its also what can make your Road Angel go loopy too). If you can't get a tacho driver to match your ecu to the tacho then you may have to change the tacho. Depending on your ecu, a cerbera one may work.

Ian.

[AntonyJ]

Cheers guys, just trying to get my head around the wires/connections between the lucas ECU (which I see as virtually stand alone) and the rest of the car.
With mine being an early car, there is no plug for these wires.

Does anyone have a list of the common connections between ECU and car?

Mains power (switch ignition)
Ground
Fuel pump
Tacho
Speedo input

What else is there likely to be?

Will have to speak to emerald about driving the tacho. Dont really want to swap the tacho at all.

[griffter]

AntonyJ said:

Cheers guys, just trying to get my head around the wires/connections between the lucas ECU (which I see as virtually stand alone) and the rest of the car.
With mine being an early car, there is no plug for these wires.

Does anyone have a list of the common connections between ECU and car?

Mains power (switch ignition)
Ground
Fuel pump
Tacho
Speedo input

What else is there likely to be?

Will have to speak to emerald about driving the tacho. Dont really want to swap the tacho at all.

Hey Ant. It's a bit tricky due to the RR ECU/loom, VW fuse box and Vauxhall switchgear. But:

Mains power (switch ignition) - ignition switches power to fusebox which switches power to the ECU. This in turn switches the control earth of the two metal relays, and bob's your uncle, everything powers up.

Ground - various to the ECU. One earthed on the fuel rail, one earthed on the back of the n/s cylinderhead. You'll find more pins are described as earth, but they connect together in the loom by the ECU plug. I ended up connecting mine all together and connecting those to the battery negative.

Fuel pump - powered from the fusebox, controlled by the ECU.

Tacho - off the coil -ve before the resistor to the ECU rpm input.

Speedo input - think this is direct from the speedo sensor.

I'd pop out the garage to get the wires colours for you but...

[spend]

I think Ants might be a bit different Ben, IIRC some early pre-cats have one/both of the ecu relays in the fusebox

Its easier to work from what your new ecu needs IMHO, test & label them up first.

[AntonyJ]

spend said:

I think Ants might be a bit different Ben, IIRC some early pre-cats have one/both of the ecu relays in the fusebox

Its easier to work from what your new ecu needs IMHO, test & label them up first.

Mine does have a fuel pump relay in the fuse box, and both of the relays in the ECU harness.

Thats exactly what I want to do Dave, work out what is there now and adapt to what is going there, remembering that I want to be able to sell on the engine and ECU/loom as a useable item.

[spend]

You should be able to pull out the engine loom pretty quick Ant, no lambdas, purge valve..

The other connections OTOMH are:
coil -> tacho + ecu
speed sensor -> blackbox~(?) -> speedo + ecu
2 big browns to fuses &or relays on ecu loom
1 big earth to ECU
ign 12v to ecu (might be from the fusebox relay)
Fuel fuse (after relay) goes to inertia switch / immob..fuelpump.
Might be a wire from ecu to fault light (MIL).

Cant think of any others at the mo

Not sure how many would want a 'catless' loom though mate? only other pre-cats maybe..

[AntonyJ]

Not sure if it is catless Dave, seem to remember seeing Lambda plugs last winter....

[spend]

Sorry Ant, I always come up with Ant = pre-cat for some reason

Lambda looms just unclip on the chassis and around the injectors.
The purge valve/ carbon wiring goes up the dash and out into the wing over the heater.

[AntonyJ]

Your right Dave, precat all the way.....


mmmm 4.6 ,no cats.....

[AntonyJ]

This is the set of wires coming from my ECU to car loom.....

[LordGrover]

AntonyJ said:

Your right Dave, precat all the way.....


mmmm 4.6 ,no cats.....

A couple of precats at c.270 ... I wonder what a 460 will produce ...