Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[WinRAR]

Seems that the CC on my Omega is not working right. This is something my car has been doing since I bought it. I thought it was normal, blamed the auto nature of the car and didn't care about it, but in a recent trip a friend said it was not normal, so I'm posting to ask it.

The car is an auto 2003 3.2 with factory fitted Cruise Control. The gadget works, but it doesn't "lock" the speed as my friend says cruise controls do. When I set the speed, the car takes sometimes (not always) some seconds to (apparently) think about what I did and loses some speed. When climbing, it loses some speed until it finally shifts down and pushes like a beast.

I can understand the downshift in climbs, but the worst is probably  when going downhill. That was what made my friend point at the CC not working right. In such situation, the car simply doesn't hold the speed. It always goes a good number of miles (~6/7) faster than the set speed 

Isn't Cruise Control supposed to smoothly keep the speed? Won't it hold the car at the exact speed set by the driver in (moderate) downhills? The why does mine act like it does?

Can loose cables or something like that cause the CC to act like that?

[tunnie]

I'd give the throttle body a good clean, on 3.2's the throttle is electronically controlled.

It is a bit of a beast, I usually set mine at 80mph, if you re-engage it at 50, it gets you to 80 as quickly as possible.

But its never more than 2/3mph out of the set speed, wonder if the throttle butterfly is sticking a bit 

[WinRAR]

It is a bit of a beast, I usually set mine at 80mph, if you re-engage it at 50, it gets you to 80 as quickly as possible.

Yes. I'll understand it pushing if I recovered the stored speed from a reasonably lower speed. But why does it (and it alone) lose that much speed to force itself to push like a beast?

But its never more than 2/3mph out of the set speed, wonder if the throttle butterfly is sticking a bit 

I'll check that. But it doesn't explain why the car doesn't hold the speed when going downhill.

So, it is right that CC doesn't usually work like it does in my car?

[Jimbob]

There is a tech2 engine upgrade for the 3.2 which affects cruise control.

But this sounds different to what that fixes, which iirc an improvement of the resume function

[tunnie]

I'd be a bit concerned with it going 7mph faster than set speed, unless you are on a serious bit of long fast downhill run.

Down big hills here at motorway speeds, it still keeps to within 3mph ish for me in either the 3.2 (Auto) or 2.2 (manual)

If the throttle body is sticking, it could show why its not slowing down at speed when at a hill, as it should close the throttle almost completely off.

[Marks DTM Calib]

I seem to recall the engine software update mentioning cruise on auto vehicles.

[Kevin Wood]

Remember that all the cruise control can do when descending is to coast, so if the hill is steep enough it'll overspeed.

What speed are you using it at? Mine is terrible at low speeds -  say below 40 MPH. The cruise and autobox seem to fight each other. At main road / motorway speeds, say above 50MPH, it's rock solid, though.

I would expect the engine ECU to complain if the throttle were sticking mechanically, since it's under closed-loop control. It'd also be evident in normal driving.

Might be worth seeking out the update of you have a Tech 2 close.

[WinRAR]

Remember that all the cruise control can do when descending is to coast, so if the hill is steep enough it'll overspeed.

What speed are you using it at? Mine is terrible at low speeds -  say below 40 MPH. The cruise and autobox seem to fight each other. At main road / motorway speeds, say above 50MPH, it's rock solid, though.

I would expect the engine ECU to complain if the throttle were sticking mechanically, since it's under closed-loop control. It'd also be evident in normal driving.

Might be worth seeking out the update of you have a Tech 2 close.

I also think the throttle body is fine. Otherwise I would have noticed it in normal driving.

I'm locking the CC at ~60 mph (100 km/h). That's the speed the car can't maintain when going downhill.

The Tech 2 update is very interesting. I'm checking it as soon as I can.

[TheBoy]

As other say, it can speed up down hills.

At 60, approaching a steep incline in top gear, its not really in its power band, so may loose a bit of speed, before kicking down a gear...

[Kevin Wood]

As other say, it can speed up down hills.

At 60, approaching a steep incline in top gear, its not really in its power band, so may loose a bit of speed, before kicking down a gear...

Yep, gearbox is reluctant to change down at around that speed too, I find, so cruise control gives it a fair bit of throttle trying to pull through the flat spot then it takes off like a bat out of hell once it does change down.

[Andy H]

As other say, it can speed up down hills.

At 60, approaching a steep incline in top gear, its not really in its power band, so may loose a bit of speed, before kicking down a gear...

Yep, gearbox is reluctant to change down at around that speed too, I find, so cruise control gives it a fair bit of throttle trying to pull through the flat spot then it takes off like a bat out of hell once it does change down.

My 2.6 behaves similarly (but at a lower road speed due to the shorter gearing? ).

I find that using the sport button helps to smooth out the gearchanges by changing down before the throttle is wide open......

[steve6367]

This is interesting reading for me as I was going to write a similar post. Trip to Oxford up A34 a few days ago, CC set to 65 and on every little hill the box dropped a grear. I was surprised by this, but then not had an Auto with CC before. In the Vectra (1.9 TDCI manual) it will sit in 6th with CC at 65 on any dual carrageway motorway without differculty.

I also note that if I drive the Omega myself without CC the auto box will hold top grear on a much steeper hill.

Is this normal? Or should I be able to to cruise in top gear?

Steve

[tunnie]

2.2 Autos will drop down at slightest opportunity on cruise, my 2.2 stays in gear as its a manual.

3.2 I have changes down lot less on cruise, but that does have a lot more torque.

[Kevin Wood]

There are some fairly decent climbs on the A34.

You have to consider how the cruise control works. It's basically a PID controller that compares the road speed to the "set" speed and generates throttle output to maintain the two speeds constant.

It will make small throttle adjustments while the differences between the speeds remain small (i.e. on the flat) but if a steep incline causes the speed to drop more quickly, and if the car is also bogged down in a high gear and doesn't respond as quickly to throttle input, it will make increasingly large throttle inputs until the speed is maintained. It can't anticipate the hills like a real driver would. It waits until the speed has started dropping before increasing throttle. It can't anticipate gearbox shift points and avoid unnecessary downchanges like a driver might. It also won't tolerate a small drop in speed like a real driver would. It will try its' utmost to pin the speed at the "set" speed, so that might result in gear changes that would be avoided by inputs from a "real" driver.

[steve6367]

Kevin, thank you - that does make sense. I read earlier in the post about software update for cruise, does that help at all? It strikes me it could do with a bigger error band so it allows some change in speed.

Steve