View Full Version : Q4 re wire.

18-11-10, 23:51
Hi all. I am planning on doing a complete rewire of my Q4 over the summer (that's the summer that's almost here in Australia...). I am planning on removing every wire (every wire) and starting again from scratch. I want to remove all the relays and switches and the complete engine loom. I am also planning on fitting an aftermarket ECU at this time (an Autronic SM4). I plan on making the wiring much simpler that it currently is.

It all looks pretty straight forwards EXCEPT for the wiring to the ABS system. Here is what I want to know..

1. Is the ABS system complete within itself - are there wires that go from the abs controller (under the rear seat) to the ABS unit its self?

2. Is it clear where to supply the ABS controller and unit with power and ground?

I'd like to be able to retain the use of the ABS system with the bare minimum of wires. Has anybody looked at this?


20-11-10, 12:31
You should leave ABS as it is. The wiring from/to the sensors is shielded and special cable, molded onto the sensors. You will only make it worse if you try to fix that. The multi-connectors on the unit are weak, as are the relays. On later versions the relays are soldered on to prevent loose contacts. ABS is autonomous, in that it has it's own power and has no connection to anything else. I'm not sure if it's wired into the break light switch, but that would be the only thing in common with the rest of the loom. Unless you can find new multi-connectors for the ABS, I would leave them on. There is only very minimal wiring on the ABS apart from the 4 sensors and the powerleads. An indicator light and possibly a link into the break light circuit, that's it.

20-11-10, 21:12
Thanks WizzMan, I will certainly leave the wiring that goes from each wheel to the ABS control unit alone!

Steve Webb
22-11-10, 10:08
Hi Jim, good luck with the rewire, not sure if you've got all the parts you need yet, but if not, I've used these guys before and they pretty much cover everything wiring related.

Autosparks (http://www.autosparks.co.uk/)


02-12-10, 21:36
clutch is also used for abs and ecu, and the ecu gets a signal if you're speed is up or under 30 km/h from abs system

02-12-10, 22:03
jan.. does that mean that the ABS won't function after I change the ECU as part of this re-wire project??


03-12-10, 06:05
Sounds like a lot of work Jim! Nice choice of ECU btw. Sorry can't help with the ABS.

03-12-10, 09:39
Jim, it works the other way around. The ECU limits torque at lower speeds. For that, it needs a speed signal. I haven't been digging deep enough into the Q4 yet to find out if this is a myth, or actually true, but logic dictates the ABS should function even with a non-running engine and no signals from the ECU.

Steve Webb
03-12-10, 10:48
The ECU limits torque at lower speeds. For that, it needs a speed signal. I haven't been digging deep enough into the Q4 yet to find out if this is a myth, or actually true,

This myth has been around for years in various forms, one speed based, the other gear based. The easy way would be to use a speed sensor, but then again you could make it gear related by using the accelerometers (already present in the car), throttle position and rate of change of engine speed.

Although using this method, changing the power output of the engine or going uphill or downhill would affect the system. So its probably too complicated and too subject to outside influence to have been used.

But logic dictates the ABS should function even with a non-running engine and no signals from the ECU.

From a safety point of view the ABS should still function in the case of a stalled engine or breakdown, however will they still function with the ignition completely off or the ECU removed is a different question.

03-12-10, 18:16
ABS does not function when the engine is shut off. ABS unit simply does not get electricity.
Also, there is no vacuum in the system for brake assisstance, therefore braking with engine stalled is very, how to say, 'unproductive', i.e. without break assisstance (no vacuume in intake manifold) you have to use extreme force on the brake pedal to stop the car (except the initial breaking).

Jim - why don't you through away the ABS unit and all the ABS wiring, you would have a shorter breaking distance and more control on the car, especially on uneven tarmac.

It is very easy to eliminate the ABS in Q4. Can send you photos on what to disconnect.

04-02-11, 05:46
A couple of final pictures of my new wiring setup with bias valve for the rear near the drivers seat where I can reach it!

04-02-11, 07:13
Very very IMPRESSIVE Jim! i remember one pic of your car on another thread before the re-wiring and the difference is very noticiable, the interior of your Q4 is being to be a very nice place to race ;)

04-02-11, 08:40
Thanks biggie! Its taken a huge amount of effort, but its good to have all the wiring and relays that were up under the steering wheel and everywhere else finally gone.

Now I have 16 separate circuits with fuses and 5 relays - and I know what they all do!!

Its actually a lot more effort to remove the wiring than it is to change the ECU...

speaking of the ECU change, its possible to use all the Q4 original sensors with the Autronic SM4 so it would be easy enough to make a patch cable so that you could change ECU and keep the original wiring. I am using the original OEM Cam and crank senors.

04-02-11, 09:54
That is interesting Jim - I know yours is an all out race car but for a daily driver would it be worth investing in a custom ECU? The chip in the OEM ECU is replaceable for custom maps - where are the advantages in your opinion?

04-02-11, 10:22
The Autronic SM4 is a very sophisticated ECU and is great for a race car, but I would never consider it in a road car. The standard IAW P8 ecu does a GREAT job, and is very flexible (if you get an ostrich so that you can control its tables).

The only reason that I decided to get a different ECU really is that the boost control in the IAW P8 is weak - and I was never able to make it work as I wanted. If there was a proper manual for the ECU and its data tables, maybe that would have been different, but managing 1.5 bar boost at 7000 rpm is not what the P8 is good at. A decent boost controller like the Turbosmart EBoost2 costs about $1000 - the SM4 cost $2300 - so i decided to go with the ECU instead.

The SM4 also has launch control, flat shifting, ALS - all things that only make sense in a racecar.

While I still had the standard ECU in the car, I converted the fuel to E85 and doubled the engine horsepower - showing the flexibility of the system!


04-02-11, 13:08
Cheers Jim :)