Thread: Ashcroft CDL and the SLABS ECU wire cut

Originally Posted by strangy

Having driven both a D2a with CDL (therfore later SLABS ECU) and my D2 with CDL & wire cut, there was no measurable or discernable difference.
As others have already said a couple of Psi and technique will be more noticable than an ECU change.
Thats before any consideration of suspension, tyres and loads.

cheers

I hope it was a 2004MY D2a you were driving. LR revised the SLABS ECU for the 2004MY and this is revision that is considered to be best sorted.

Bear in mind that the wire-cut also effects the other aspects of the SLABS - ABS, EBD and HDC. These all work on basis able to brake wheels independently when the cdl is unlocked. If you fool the ECU into thinking the CDL is unlocked while it is locked there are some potentially unpleasant side effects. I think I came across one when I was using the wire-cut mod, the rear brakes seem to have locked triggering the abs while I was driving through the apex of a tight down hill hairpin with a loose sandy surface.

EBD biases braking force to the leading axle as this is least likely to lose traction. With the CDL locked at least part of the braking forces applied to the front wheels are transmitted to the rear axle via the driveshafts and locked cdl, meaning that more braking force than intended is applied to the rear wheels.

It may be coincidence but I haven't had anything similar happen since upgrading the ECU.

FWIW the install is about an 30min - hour's work and setup is simply a matter of saving the settings from the old SLABS ECU before removing, then writing the saved settings to the new ECU. Piece of cake.

cheers
Paul

Originally Posted by Slunnie

Re the SLABS computer, it sounds like a good idea but I get the impression that the ETC isn't as positive as the early type, so you may be better off snipping the wire

"positive" is the wrong way to describe the difference (or what we think the difference is at least). It appears that the later revisions from the D2a's allow a slightly greater amount of spin before activating ETC on a wheel.

The pre-facelift ETC works on the assumption that you didn't have the CDL locked, and this means that any single wheel spinning has the potential to stop forward progress. The assumption is then that the ETC will react aggressively (i.e. at low levels of wheel slip) to a spinning wheel to ensure forward motion is maintained.

With the CDL locked this is not the case. A single wheel spinning means that two wheels of another axle still have grip and the ETC can cope with a higher level of wheel slip before activating - making it less aggressive in operation.

WABCO's technical documentation of it's Type-D ABS system on which SLABS is based makes note of a traction mode, which increases allowable slip to improve operation in deep snow and similar slippery conditions.

This would suggest that in circumstances where traction is limited (mud, snow and possibly sand) less aggressive (greater allowable wheel slip) ETC will work better than more aggressive operation modes. There have been threads on AULRO, for example, suggesting that the D2's ETC is too aggressive on sand allowing it to stop the vehicle by over-zealous application of brakes. On the other hand it has been also suggested that the aggressive wire-cut ETC is great for rock crawling.

Maybe the best compromise is the final revision ECU with an inline switch to allow use of the more aggressive unlocked CDL programming for rock crawling and the LR locked cdl programs for other conditions

I recognise that the late revision ECU is going to be too much of a hassle for most people to bother with, but at least for all-round/touring use it is really a very nice upgrade for pre-facelift D2 with multiple (not just ETC) benefits.

cheers
Paul

e[quote]

Originally Posted by OffTrack

I hope it was a 2004MY D2a you were driving. LR revised the SLABS ECU for the 2004MY and this is revision that is considered to be best sorted

.
Yes it was.

Bear in mind that the wire-cut also effects the other aspects of the SLABS - ABS, EBD and HDC. These all work on basis able to brake wheels independently when the cdl is unlocked. If you fool the ECU into thinking the CDL is unlocked while it is locked there are some potentially unpleasant side effects.
EBD biases braking force to the leading axle as this is least likely to lose traction. With the CDL locked at least part of the braking forces applied to the front wheels are transmitted to the rear axle via the driveshafts and locked cdl, meaning that more braking force than intended is applied to the rear wheels.

Swapping an ECU is the only option if you dont want to cut the wire, however isnt a straight forward job for most as you suggest, particularly for those without diagnostic tools.
Interesting to note your vehicle is an auto which takes some inputs from the BCU for the SLABS ECU function, where a manual does not.
The difference between a manual and auto is likely to be most influencial, I havnt had an auto off road.

Cutting the wire does not negatively impact the SLABS ECU function nor fool the car into doing something unpleasant.

Parameters for HDC and ABS operation remains unchanged.
i.e whatever the factory wanted the sytem to do for a given circumstance it will continue to do.
While the newer ECU parameters have been revisd for smoother operation. It is the CDL engagement which alters the driving characteristics.
Unpleasant side effects come from a faulty sytem or the fact that locked drivelines dont respond the way an unlocked driveline does, not from cutting the wire.

As far as EBD is concerned, for the reasons you stated, the later ECU's capability in a CDL vehicle will perform as earlier versions.
As the driveline is mechanically locked without electronic clutches or locking mechanisms, what ever happens to the front axles will directly influence the rear and neither ECU in this driveline configuration is capable of changing this.
In the context of "off road, CDL locked", EBD is virtually irellevant.
EBD is only active for greater than .3 g decelleration (medium to heavy braking).
As the function is based on wheel speed sensors rather than a accelerometer the parameters for operation are calculated rather than measured.

While operational parameters have been revised in the newer ECU, a change of tyre size from factory will directly influence these and any real world gains from a revised programme are subjective, potentially being positive and negative for either ECU types

Conversely the same influences with a locked driveline and tyre change is true for TC, HDC function and the ABS.

Having had the priveledge of having a few D2s side by side on the same terrain. it is easy to see first hand the variables affecting the SLABS ECU functions. By far the greatest influence is tyres (type, size and pressure) and Suspension.
Given an unlimited pile of parts a later SLABS ECU wouldnt make the list.

However, if mine failed I would get a later unit....but then I'd have to reconnect the wire

cheers

Seeing we can't agree on even basic points I guess we'll have to agree to disagree.

I would make the point that if someone is capable of installing an aftermarket lever, they will breeze through swapping an ecu. The process consists of dropping the cardboard trim in the passenger footwell - which involves removing 3-4 trim clips, unplugging roughly 9 connectors, then undoing half a dozen nuts. Install is the reverse. Granted not everyone has access to a Nanocom but is easy enough to unplug the cables with the SLABS ECU left in place and plug in the later ECU. This means someone wanting to do the job could call on a friendly AULROian, have the config read from the old ECU, plug in the new ECU then write the existing config. The actually swap of ECU's could then be done at leisure.

I'll be getting an updated unit plus keeping the original to carry as a spare. Then need to get a spare ECU & Auto ECU. Any others needed?

me thinks you are all over-analysing this, and anyway once you fit lockers who cares what the tc is doing!.

Hi All,

The CDL is in and working - will cut the wire tomorrow.

Before I cut the wire: Is there any reason why the TC and ABS lights are on and staying on?

Everything I read and been advised on; no-one has mentioned that these lights would come on and stay on.

Can anyone help?

Cheers.

Most likely a cable adjustment. Even though the CDL may be disengaged, it may need an adjustment on the cable to fully operate the switch.

However, If CDL engaged at start up you will have to disengage the CDL then switch off and restart the car to clear the lights until the wire is cut/ switched etc.

cheers