307 HDi DTurbo Cruise Control

Although I've owned a 307 Dturbo since January, I've only just got round to
trying out the Cruise Control, and only for brief periods owing to the
congested state of British roads. On a longish trip, mainly on motorways, I
accelerated up to 90MPH (to keep up with the flow of traffic) and set the
cruise control. After only a short distance I came up behind slower moving
traffic and had to slow down to about 50MPH. When the congestion had cleared
I re-engaged cruise and was amazed by how quickly the car accelerated up to
the memorised speed, seemingly much faster than flooring the accelerator.

At first I put this down to imagination but my wife who also drives the car
got the same impression. It's as though there's an extra boost from the
turbo. Is this a possibility?
Anyone care to comment?


--
"Once in a while,
I'm standing here, doing something.
And I think,
What in the world am I doing here?
It's a big surprise."

 

I get the same on my C5 when letting the cruise control resume the speed.
Nice isn't it?

What is more suprising is when you forget what your last speed was, say
70mph, then when you doing 30ish in 4th and hit the resume button you will
get there very quickly indeed!

Nice cars

Ben

 

I've the same model. At first I thought the cruise control would be a
novelty, but I couldn't do without it now, especially on long
journeys. Even on congested roads, it's helpful to drive with it on
to even out the 'speed-up-brake' mentality of the likes of the BMW
drivers. I use the c/c to accelerate and decelerate rather than the
pedal.

I don't think there's a 'boost' in the output; it's just that the
electronics reacts a lot faster to the changing engine speed than your
right foot can. After all, you shouldn't just floor the pedal when
you want to increase your speed; you should allow the revs to build to
prevent wasting fuel.

 

I get the same on my C5 when letting the cruise control resume the speed.

Very nice indeed. I now realise what I've been missing for the last 6
months!

I must try that!

 

I was of the same opinion - a novelty - until I used it. It's nice to show a
clean pair of heels to a tailgating BMW!

Perhaps the ECU uses a different program rather than a turbo boost? Normally
I never floor the throttle for economy reasons but did so as an experiment
in this case.
Another thing that impressed me was the absence of wind and engine noise -
seems to reduce above 70MPH. I really like my 307!

 

Interested to hear someone else noticed this. I thought I was going mad but
swore it is a lot quicker.

If anyone knows the real technical reasons for this I'd love to hear them.
Surely with all the electronics in the car if you put your foot right down
on the accelerator it should do its best to go as fast as possible - the
accelerator is not mechanical on the 307?

 

I have noticed the same effect in dad's Volvo (don't have CC in my 206).
I put it down to psychology. In the volvo the CC is electro-mechanical (it
presses the accellerator for you) so there is certainly no trick going on.

Maybe the fact that you are not directly in control of the car enhances
the experience, making it seem that little more scary/fast. Try sitting
in the passenger seat and do the experiment with CC and driver and see if
you notice a difference?

Gerd.

 

Probably not necessary to mention but noticed a couple of posts regarding
peeps using CC for the first time here. Please be advised not to use this
on wet surfaces as any loss of traction to the wheels in wet conditions
with the CC turned on can lead to a very scary experience.

Found this out personally last year when Aqua-planing due to having CC
engaged in the middle of a down-pour. Car was quite happy on motorway
until it hit a patch of standing water, the wheels lost traction and the
CC tried to get the car back to memorised speed. When the tyres got some
purchase back the resulting skid was terrifying, fortunately no-one was
hurt and managed to have the sense of mind to apply gentle braking and got
car under control again.

Just thought I'd share it, as wouldn't recommend the above to anyone but
adrenalin junkies!

 

I agree that it could be all down to imagination from not being in direct
control of the car but during my experiments with CC when my wife was a
passenger, she also commented on the apparent faster rate of acceleration.
One thing I haven't mentioned is the 'kick' when CC is engaged, similar to
'kick down' in an automatic. This is especially noticeable when engaging CC
from say 60mph in 5th gear upto a memorised speed of 90mph.

 

Thanks for the warning! On the 307 Dturbo, traction control and ESP are
standard equipment. Just wondering how they would cope with such a
situation.

 

The fact that the CC is controled electronically means that the sensation
of speed is more instantaneous. I don't know if its true of Pugs but a lot
of CC systems are controlled by and actuator which is independent of the
normal accelerator set-up. The CC system is designed to get you to your
chosen speed quickly without overshooting it.

So for those people having set the CC speed to 70mph and who then
re-engage the last memorised speed from a relayively low speed e.g 30mph
will notice a seemingly aggresive accelereation back up to your desired
cruise speed. As such the 'flooring' of the accelerator pedal won't
recreate the same experience as CC controlled acceleration because all
your doing there is opening the throttle and adding more combustible
material to the mix which eventually leads to greater acceleration.

There isn't a 'kick-down' as such just a more efficient and faster
electronically controlled acceleration of the combustion process.

 

Has anyone noticed whether fuel economy is better or worse when using CC? I
don't actually use mine that much so can't really comment.

 

It says in the C5 manual that the CC will disengage when the ESP is
triggered.

 

That's comforting to know!

 

Not doing a great deal of motorway driving myself, I find CC more useful
when driving through 30 or 40 mph zones. Assuming there isn't much other
traffic around. I can set it to say 33 mph (!), then not have to worry about
continually checking my speed, especially with so many speed cameras in my
area.

Robin

 

Agreed

 

You can add it to most new HDI engines (the ones with the radio controls on
a big stalk)

Ask your dealer if they can do it.

The procedure is as follows:

1, Fit CC stalk.
2, Ensure brake and clutch switches are present, fit if they aren't (I didnt
have a brake switch)
3, Tell the ECU it has CC.

Total cost at a UK main Citroen dealer: £125.

 

The 307 HDi solded down under are Not fitted with Cruise Control.


Keith