Thread: overdrive and cruise control

I suspect you are correct and as the cruise control is a function of the ECM then I suspect it can't be changed unless something can be done with the vehicle map data. That said the Disco2's ECM has the cruise control functionality disabled, so I assume the vehicle mapping does this. I think you need to get in touch with someone who really knows the ECM programming.

i also have an remaped ECM giving 140kw and i asked the people who did this and they said that there was very little chance of finding the map that controls this in the ECM as there are many 100's of maps with 100's numbers and just one number controls this. i dont think they wanted to try. i was hoping someone may have found a way around this or know where in the ECM this control is.

Originally Posted by dm_td5

.... That said the Disco2's ECM has the cruise control functionality disabled....

Please explain! I cannot make sense of this comment.

Originally Posted by paul-defender

.. with the overdrive engaged the cruise control will work in 3rd and 4th but not 5th. it is like the computer picks up a difference in road speed and engine revs and dissables the cruise control....

The ecu works-out what gear is being used using engine revs and road speed. The ecu probably thinks 3rd & 4th are 4th and 5th, but your higher gearing in 5th has it thinking 'this does not compute!', so doesn't allow CC.
I get the same sort of result using HDC in my D2 in high range when I tell the ecu I'm in low range - HDC works in 3rd high so the ecu probably thinks I'm in 5th low. I could check the ratios but I'm too lazy.

Paul,

Let it go. Unless you want to carry out an accademic exercise to see if you can fix it.

Although your engine has been chipped and may well produce the goods and push that 5th plus OD, I would not expect 5th gear to last very long pushing that aerodynamic brick at speed with the OD placing additional stress.

For people who want to push a speed and lower engine revs (as per 5th gear) while towing it is recommended that they use 4th plus an OD like you have. Even the user manual will recommend that you not tow in 5th.
The box will last much longer if used in 4th and the OD will drop the revs.

Originally Posted by slug_burner

Paul,
...I would not expect 5th gear to last very long pushing that aerodynamic brick at speed with the OD placing additional stress.

For people who want to push a speed and lower engine revs (as per 5th gear) while towing it is recommended that they use 4th plus an OD like you have. Even the user manual will recommend that you not tow in 5th.
The box will last much longer if used in 4th and the OD will drop the revs.

Maybe Im being stupid here but I dont understand the logic behind above?

What difference woud it make being in 4th or 5th (with or without OD) when towing? As far as I can see you only lower the revs of the engine. The danger there is that you make the engine labour and I suppose need to change gear more frequently which will place more stress on the clutch and labouring does no favours for the Dual Mass Flywheel - but anyone who can drive reasonably well will hear the engine note alter and change gear accordingly.

As the gearbox is a precision unit there should be no lateral forces across bearings to consider which would soon destroy a box, rotational speeds are less so heat build up is less...

Im puzzled. Perhaps someone would care to explain.


As for the CC and OD not working together. I can speak with more authority on that. It is a problem, and as others have said, when the revs drop below a certain point and all other things are taken into account it simply falls out of spec in the ecu and refuses to work. Much in the same way that you cant operate the CC at below 40kph (from memory).

Regards,
Jon

That is the problem with computers, they only do as they are told and anything outside their design operating parameters sends them into a tailspin... Basically they are stupid and can't 'think' for themselves.

Paul, now you're back in Tassie, I suggest you sell the o'drive as you aren't going to need it now...even with all that torque on tap

JC

Originally Posted by Yorkshire_Jon

Maybe Im being stupid here but I dont understand the logic behind above?

What difference woud it make being in 4th or 5th (with or without OD) when towing? As far as I can see you only lower the revs of the engine. The danger there is that you make the engine labour and I suppose need to change gear more frequently which will place more stress on the clutch and labouring does no favours for the Dual Mass Flywheel - but anyone who can drive reasonably well will hear the engine note alter and change gear accordingly.

As the gearbox is a precision unit there should be no lateral forces across bearings to consider which would soon destroy a box, rotational speeds are less so heat build up is less...

Im puzzled. Perhaps someone would care to explain.


Regards,
Jon

Towing heavy / wind resistant loads in 5th gear is a sure fire way of destroying gearboxes.

When there are gears in mesh such as in a gearbox, any load on them will impart a separating force. The higher the load (5th gear towing) the higher the separating forces.

These forces will prematurely wear bearings and can cause engough flex to allow the gears to "fall out" of correct mesh. The gears are then prone to failure.

Generally speaking, 4th gear in most gearboxes is a "straight through" gear. It couples the input and output shafts together, rather than passing the torque through a meshed gearset. Hence 4th is a better gear for towing.