Disco 1 unusual cruise behaviour?

Hi all,

Perhaps someone can shed some light on the problem I am having with the cruise on my ’96 300tdi auto…
When I bought it the cruise was not working at all, since then I have trimmed the split ends on the hoses and discovered that the ‘set’ switch in the steering wheel also doesn’t work. I have swapped this with the ‘decel’ switch to test if it is working.
I am now getting some life out of the cruise, when I set it to a speed it is holding that speed for a short while before slowly dropping off, when I tap the accelerator pedal the cruise moves the accelerator pedal down and accelerates me back up to the speed I set the cruise at. Once it gets to that speed it starts to decelerate again.
Anyone got any idea what could be causing this? I have already fixed two things that were stopping it from working, it seems like every part that could break has done!

Thanks,

Dave

You still have an air leak. Check the ends again also the hard to get at one at the pump in the area under the jack also the dump valve at the accelerator pedal although the rubber hose seems only to perish at the joints in the engine bay due to the heat. Put a few laps of pvc electrical tape around the ends of the hose before refitting and u won't have a split hose end again.

Not had a chance to look at the pipes yet but i managed to take it on a motorway run and it seems like the cruise is able to hold the accelerator pedal in position to get back up to the speed I set after it has dropped, but when it releases the pedal once it reaches the set speed it doesn't appear like it is able to re-accelerate (ie depress the pedal) to maintain that speed. Does this sound like it is an air leak?
After I cut the split ends off i tested by sucking on the pipe by the pump, below the jack, and putting my thumb over the end and it seemed to hold the vacuum as the diaphragm didn't got back out again.

When the split end has been cut off the hose can easley split a again when pushing it back on hence the pvc tape trick other than that it's replace the hose with 4.5 inside dia thick walled pvc hose at £3 or silicone hose which comes in nice colours which is about £10 + pp for 4 metres.

I've had your CC symptions not working or working but not maintaining the fixed speed it's a common fault.

Regards

discool said:

When the split end has been cut off the hose can easley split a again when pushing it back on hence the pvc tape trick other than that it's replace the hose with 4.5 inside dia thick walled pvc hose at £3 or silicone hose which comes in nice colours which is about £10 + pp for 4 metres.

I've had your CC symptions not working or working but not maintaining the fixed speed it's a common fault.

Regards

Click to expand...

Hi discool, I'm interested in where you get this silicone hose from. It would need to be mail order for me as I don't live in England, but it sounds like an ideal long-term solution.

Hi thebiglad, have a look at this link thats where I will go shopping one day. But also do a silicone hose internet search as there may be an auto 'gofaster' shop local to u in France.

Link: http://www.venairsport.co.uk/

Regards

discool said:

Hi thebiglad, have a look at this link thats where I will go shopping one day. But also do a silicone hose internet search as there may be an auto 'gofaster' shop local to u in France.

Link: http://www.venairsport.co.uk/

Regards

Click to expand...

Thanks very much for that Discool, it looks as though they import into France.

Very exciting products - I think the underbonnet of our two Discos are about to look a lot smarter.

An update...

Finally got round to changing the hoses for new silicon vacuum hoses and the same problem is still there. The vacuum is capable of holding the accelerator in position but not capable of actually pulling it down on its own so once the cruise reaches the set speed and eases off the accelerator it is not capable to pull it back!
I have sprayed a load of wd40 down the sleeve that the cable, between the diaphragm and the accelerator pedal, runs down as it felt like the cable was sticking and it seems to move a lot freer now but still the problem wont go away!
Does anyone have any more suggestions as I am running out of ideas!


Thanks,

Dave

Sorry to say it but my be your vacuum pump thats faulty as always with a lot of things its 'test by replacement'. Remember there are two types, petrol and diesel pumps are different. It can only be that the pump is incapable or that there's a leak in the system somewhere.

It has been a while but i have finally got round to changing the vacuum pump and it is still behaving in the same way.

When i set the cruise to a speed it will not be able to hold it. If i then depress the accelerator the cruise will hold the pedal in position when i take my foot off and accelerate me back up to the set speed. When it reaches that speed it eases off the accelerator and the speed starts to fall again...
Any ideas? I have now replaced the hoses, one switch that wasn't working (all others fine), and the vacuum pump.

Thanks,

Dave

disco-dave said:

Hi all,

Perhaps someone can shed some light on the problem I am having with the cruise on my ’96 300tdi auto…
When I bought it the cruise was not working at all, since then I have trimmed the split ends on the hoses and discovered that the ‘set’ switch in the steering wheel also doesn’t work. I have swapped this with the ‘decel’ switch to test if it is working.
I am now getting some life out of the cruise, when I set it to a speed it is holding that speed for a short while before slowly dropping off, when I tap the accelerator pedal the cruise moves the accelerator pedal down and accelerates me back up to the speed I set the cruise at. Once it gets to that speed it starts to decelerate again.
Anyone got any idea what could be causing this? I have already fixed two things that were stopping it from working, it seems like every part that could break has done!

Thanks,

Dave

Click to expand...

I suspect that there is still a perished pipe somewhere that you haven't yet found as it sounds just like it's losing vacuum, to me.

Good luck

Dave

I think i have finally attributed the problem to the cable between the pedal and the diaphragm as the problem. it seems to be sticking! A new one is on order, hopefully it will do the trick!

disco-dave said:

I think i have finally attributed the problem to the cable between the pedal and the diaphragm as the problem. it seems to be sticking! A new one is on order, hopefully it will do the trick!

Click to expand...

I've just had a thought about this cruise control problem.

Did you say that you swapped the 'set' button on the wheel for the other one?

If so, then maybe it's an electrical fault. The reason why I say this is that the button you swapped with the 'set' button has two functions, the first is to reduce cruising speed and the second is the 'resume' function.

If I understand your description correctly (and there's always a doubt about that ) then I think what's happening is the there are conflicting eletrical signals being sent to the control unit by the foot switch and the wheel switch - it sounds like it's always trying to 'resume' when you press the accelerator.

Hope I'm explaining this right??!!

Cheers
Dave

I was just thinking the same before I saw your post biglad. Find a replacement origional switch from a brakers and try it again.

I had the same problem on my v8i disco... I replaced the pipes.. still had the problem. replaced the switches still had the problem. eventually i discovered that the vaccuum chamber on the throttle housing was porus. (easy way to check.... build the vaccum up and try pulling the rod that controls the throttle out of the housing.. movement and its moshed. no movement its fine. (don't forget to seal the rest of the system out with something like a hose clamp) Worth checking! Good luck. PS