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Cruise control and fuel economy

Submitted: Friday, Feb 02, 2007 at 11:21

Im.away

Do you get better fuel economy using cruise control or driving manually? I hear conflicting stories but with me the cruise seems to win...
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ThreadID: 41888 Replies: 7
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AnswerID: 219207   Submitted: Friday, Feb 02, 2007 at 11:42

Robin replied:

Its a individual thing up to the driver.

You can potentially do better manually , but most lose the discipline after a while.

Robin Miller
Reply 1 of 7
FollowupID: 479732   Submitted: Friday, Feb 02, 2007 at 12:00

Im.away posted:

That's me I'm afraid...the old "are we ever going to get there" right foot comes into play too often.
FollowUp 1 of 5
FollowupID: 479734   Submitted: Friday, Feb 02, 2007 at 12:12

Robin posted:

Yes Iamaway , you have to practical.

The main issue with cruise is over acceleration up a hill , and car doesn't know its going up and just juices it. Then over the top your going to fast , which can be a bit hair raising at times in my ca which has a lot of power.

I find best is to leave on cruise on relatively flat terrain and as going up a big hill I just cancel and press resume over the top.

If I feel car will do it , instead of cancel I just kick it into neutral and roll the hill.

Robin Miller
FollowUp 2 of 5
FollowupID: 479793   Submitted: Friday, Feb 02, 2007 at 14:49

Member - Oldplodder (QLD) posted:

Thats why Mercedes, BMW etc noe connect the brakes into the cruise control.
If engine braking is not enough , the puter puts on the brakes.
I think they need a smarter puter in the first place!

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John C - aka Oldplodder
In touring mode, the way it should be.
FollowUp 3 of 5
FollowupID: 479803   Submitted: Friday, Feb 02, 2007 at 15:26

Member - Davoe (Nullagine) posted:

doesnt rolling in neutral stuff the trannie? (probablly not in that distance but with a 3 grand plus box I wouldnt be trying to save .5c of fuel)

Assuming of course you are talking of an auto
you dont need to leave perth to go bush
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You dont need to leave Perth to go bush
FollowUp 4 of 5
FollowupID: 479864   Submitted: Friday, Feb 02, 2007 at 19:51

Robin posted:

No Dave I'm talking about a manual ,is not worth it in an auto.

Some auto's like a RAV4 I drive can not easiy be flicked into neutral without conncentration anyway, whereas it can be done automatically in a manual (I had to get that in).

But it would not stuff an auto -( we are talking occasionally for 2-3 hundred meters a time).

Robin Miller
FollowUp 5 of 5
AnswerID: 219217   Submitted: Friday, Feb 02, 2007 at 12:16

Steve63 replied:

Depends on the terain and your driving habits. Previous car had cruise control and I could easily get better economy driving myself. The wife tells me I drive like a grandpa so maybe that is it. :-)

Steve
Reply 2 of 7
AnswerID: 219238   Submitted: Friday, Feb 02, 2007 at 13:12

Angler replied:

Flat country cruise wins, (with less speed fines also) hilly and mountainous country manual wins. You don't floor it to get to the top at same speed.

Pooley
On the road to Kakadu.
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"...DEATH is natures way of telling you to slow down..."

Reply 3 of 7
FollowupID: 480076   Submitted: Saturday, Feb 03, 2007 at 20:20

Red One posted:

well done
FollowUp 1 of 1
AnswerID: 219315   Submitted: Friday, Feb 02, 2007 at 18:06

Member - Stephen M (NSW) replied:

Had cruise on the old (VX01) commodore (no need with hilux flat to board all the time anyway LOL) As said above on the flats great but when I see a hill approaching I like to accelerate gently where as I found the cruise would hit the hill then go ah sh@t were on a hill need more power bang pedal goes down drops back a cogg or two (auto) revs the bleep ter out of it till over the hill then will drop back into overdrive and as mentioned above your over the speed limit and then it would settle its self down again till the next hill. This was factory fitted. Was even worse then towing. On the flats great. Would I pay to have it fitted, myself no but other people do and love it. Personal preferance. Steve M

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What A Life
Reply 4 of 7
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AnswerID: 219345   Submitted: Friday, Feb 02, 2007 at 20:07

Philip A replied:

A good driver can get better economy than a cruise control in hilly country especially. I think on the flat not much difference.
One thing a cruise has taught me is not to back off on gentle curves, then reaccelerate. If you just keep going at the same speed economy is better.

BTW, slipping into neutral in an injected car will use more petrol than overriding .
Nearly all modern injected cars will cut off the fuel to the injectors if you take your foot off the accelerator while moving with engine revs above idle.
Therefore they use NO petrol downhill.
This is also a habit worth cultivating. Take your foot right off the accelerator down hills.
Regards Philip A

Reply 5 of 7
FollowupID: 480016   Submitted: Saturday, Feb 03, 2007 at 16:26

Member - Stephen M (NSW) posted:

Hi there Philip, I disagree with that theory, if the fuel was cut to the injectors the vehicle would stall. My commodore which I just sold even going down hill in overdrive would still be showing at least 1500 rpm going down hawksbury on the f3 the new toyota I just bought for my wife 06 model revs even higher with foot off the throttle going down the same hill. I would imagine this would be the case in any vehicle that if you take your foot off the throttle and the fuel wasnt delivered to the engine it would stall. And as far as putting in neutral whilst cruise control is in actve state in auto will cause the engine to rev its nut out as there has been nothing sent to the computer that you have touched the brake or cancelled out the cruise control so putting in neutral especially when going uphill will cause once again for the motor to rev up as it is wanting the power to maintain the speed but with it in neutral is unobtainable then the only way to stop it revving its guts out is to cancel either by foot brake, clutch pedal if manual or turn the main cruise off. Putting any vehicle in neutral and coasting along unless about to pull up at lights which I do (cheaper to replace pads than a clutch) to me is totally dangerous as you have no control over the vehicle in an emergeny situation. Steve M

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What A Life
FollowUp 1 of 2
FollowupID: 480087   Submitted: Saturday, Feb 03, 2007 at 21:10

Off-track posted:

...I had no control reading that reply - hardly a punctuation used.

FollowUp 2 of 2
AnswerID: 219478   Submitted: Saturday, Feb 03, 2007 at 17:08

Philip A replied:

Sorry mate but I can assure you that at the very least a Range Rover 3.9 and BMW M3 and a Mazda121 all have this feature.
The auto or manual transmission keeps the engine turning.
All of these cars I own or have owned and all have injection cut off on overrun.
I am SURE that every modern petrol engine has this and more besides .
I have also experienced this feature on all modern Commodores and Falcons
The injection turns back on when the revs get to a predetermined point , usually about 1200RPM or when you put your foot back on the accelerator,the TPS (Throttle Position Sensor) tells the injection to restart.
If you want to come to my place I can show you on the instantaneous fuel economy read out on my BMW or you can hear the quiet when my loud Range Rover exhaust becomes silent.
Get in a Commodore with instantaneous read out and you will see it.
Often older injected cars get a flat spot at the bottom of hills , because the TPS gets a wear spot just off idle.
You may have experienced some of these things
-Surge at 1200RPM as you are stopping
-flat spot on resuming
and not known why.
I refer you to
"Theory and Practice of Bosch Fuel Injection"
regards Philip A
Reply 6 of 7
AnswerID: 219484   Submitted: Saturday, Feb 03, 2007 at 17:14

Philip A replied:

On re reading your post, you seem to think I said put it in neutral. I did not. I said just take your foot off the accelerator.
The drag of the auto (in drive) keeps your engine at 1500RPM,.
The ignition is still going so the injection knows what the revs are.
Some other features of the Holden you may not know about is that the injection progressively leans off to about 16.5 :1 if the acceleratoris held constant for a period of time and revs are between parameters. This is why your Commodore may feel "soggy" when you go to accelerate after cruising along for a long time.
Thye do every trick in the book to increase fuel economy.
Regard sPhilip A
Reply 7 of 7