Adsy01

hey guys..

ive got a JDM S4 'vert thats factory turbo and Auto.
got my mtx8l in and got no cruise control..
i looked up the wiring diagrams for it and shows an input from the std ECU, im guessing its a earthed swich, but what triigers it? as there is already a speed input and a auto input...

I also have no tach output from the MTX8L (it's been checked out and is a ECU fault and is getting sent back to microtech soon along with a non-working fuel pump relay trigger wire), would that have anything to do with it?

thanks

Icemark

On the US spec S4 cars the cruise gets its signal from the summed and buffered signal from the trailing coil (as does every other thing needing a tach signal).

I am assuming that the MTX 8L is some sort of coil controller or fuel enrichment???

Adsy01

Yes the MTX-8L has coil drivers, it has its own summed tach out signal but my ECU is faulty and there is no tach out.

so if the cruise dose need a tach signal it wont have one until the tach output is fixed. (didn't look like it in the FSM though?)

the ECU is getting sent off today so should have it back in 10 dyas fingers crossed.

Thanks

Icemark

I am sorry I don't think I was clear...

There is no tach signal out of the ECU for the auto tranny or the cruise.

In fact there is no tach signal out of the ECU for anything! There is only the output driver for the leading coil, and the dual drivers for the trailing coil.

If the cruise is not working then either your dash is not hooked up to the speedo cable, or your trailing coils are not wired correctly.

You can not use an aftermarket signal to drive the cruise or the auto tranny.

Adsy01

sorry, i dont think i was too clear either...
The coils are aftermarket bosch items controled by the MicroTech MTX-8L which is a stand alone after market ECU. the std ECU is now long gone.

I wasent saying that the tach signal comes from the STD ECU...
I ment that if anything is reliant on a tach signal that it would normaly get from the std coils (tacho, power steering ect...), it wont be getting any signal at the moment.
due to the way the aftermarket coils work, you cannot get a tach reading from them (it reads half the rpm). To overcome this the MTX-8L ECU has a tacho output which replaces that signal for all tach signal needs.

the auto trans is working fine, just no tacho (A fault with my MTX-8L which i dropped off today to get fixed) and the cruise dosent work.

if the cruise needs a tach input from the std coils then that is my problem and not the mystery wire. It will get a tach signal once my MTX-8L is fixed.
the cruise was working fine before the MTX-8L and the dash hasent been touched.

so, back to the orginal question,
in the wiring diagram for the cruise there is an addtional wire shown for the automatic cars. This wire is in the same circut as the brake and clutch cut outs(as in if it earths the cruis will turn off).
the diagram simply says to ECU (or what ever they call it). but on the ECU digram the wires is no were to be seen..
i want to know under what conditions is the wire ment to be triggered?

thanks again foir your help

Icemark

yeah that extra wire is for the gear position, so that if the car gets knocked out of gear, the cruise turns off.

Adsy01

you sure thats is from the ECU?
there is another wire that goes to the auto control unit, i thought that would of been that?.
it is possible the "to ecu" is a misprint in the FSM i guess


thanks

Icemark

I think we still were mis-communicating, you said: which was the wire I described going between the Auto tranny controller and the cruise control with ties ins to the brake and gear selector (since there is no clutch on an auto tranny car).

So, maybe this will make it easier:

Between the auto tranny ECU and the engine ECU there is a inhibit switch wire (Black/Yellow non ABS -Brown/White w/abs- for gear positioning while starting) A Black/red (again for gear position while starting)- basicly both end up making it so the car can't be started in gear. There is also a Black/Blue feed from the oil pressure and the vacuum switch that the AT ECU ties into for the ECU to switch on the air pump when the tranny is in top gear and oil presure is sufficent.
Between the engine ECU and the cruise there is no connections on a auto tranny car (on manual tranny cars, the ECU and cruise do share the clutch in neutral input however).

and between the cruise and auto tranny ECU there is: a brown wire that is part of the gear selector circuit and tells the cruise that the car is in or out of overdrive.

Maybe that will help?

Adsy01

thanks again :-)