Does everyone else's cruise control "pump" on and off?

TBennet · 9th January 2018, 07:50

Hi there,

I've owned a 190 ZT-T for a little over a month now.

Do all 75s/ZTs exhibit this obvious "pumping" behaviour on cruise control where the ECU applies power for a few seconds until it's slightly over speed, then comes off the power until it's slightly under and repeats like that endlessly?

Is it just MG Rover's archaic cruise control, or is mine broken?

Thanks.

JonMs · 9th January 2018, 07:53

I can't say I've ever noticed that no. It doesn't sound right. On my car it's no different to the cruise on any other I've driven.

Mgaz · 9th January 2018, 08:01

Quote:

Originally Posted by TBennet

Hi there,

I've owned a 190 ZT-T for a little over a month now.

Do all 75s/ZTs exhibit this obvious "pumping" behaviour on cruise control where the ECU applies power for a few seconds until it's slightly over speed, then comes off the power until it's slightly under and repeats like that endlessly?

Is it just MG Rover's archaic cruise control, or is mine broken?

Thanks.

Can't speak for the zt , but my old mk1 audi A6 has cruise , but the only time you really notice it doing anything is when it applies acceleration up a hill and then cuts power on the way back down the other side.

How frequent is the 'pulsing' ?

TBennet · 9th January 2018, 08:05

Quote:

Originally Posted by Mgaz

Can't speak for the zt , but my old mk1 audi A6 has cruise , but the only time you really notice it doing anything is when it applies acceleration up a hill and then cuts power on the way back down the other side.

I'm certainly familiar with that sensation in other cars. It's similar to that, but it does it on flat road, a few seconds on, a few seconds off, all the time.

It's not moving up and down by 10 mph or anything like that, it's just quite clearly going up and down between probably 69mph and 71mph every 5 or 6 seconds and you can tell when it's pulling and when it's "resting" on a continuous cycle.

smudge.g · 9th January 2018, 08:52

Hi, I have a slightly older 75 but recently made great use of CC whilst driving to Norfolk from Scotland. Only noticed the increasing revs going up hills/reducing revs going downhill as already mentioned. No 'pumping' and it certainly made the journey very easy!! Good luck with solving your issue.

SCP440 · 9th January 2018, 09:08

My ZTT is perfect on cruise but as others have said I have felt the sensation you are talking about on other makes of cars, it is usually on Turbo cars especially if they have been tweaked.

The worse one I had was a Saab 9000 Aero, tweaked to about 300bhp and the cruise was almost unusable, below 60mph it was acceptable but anything above that and even passengers were complaining after a few miles.

Does the Cruise get its speed input from the same source as the speedo on these cars? I know on some makes they use a different ABS Sensor for cruise than the speedo.

Ennine · 9th January 2018, 09:14

Quote:

Originally Posted by SCP440

Does the Cruise get its speed input from the same source as the speedo on these cars? I know on some makes they use a different ABS Sensor for cruise than the speedo.

I believe speedo is front O/S, cruise front N/S
Someone willl correct me if that's wrong

Nige

Lord of Hog · 11th January 2018, 13:18

Since roads aren't absolutely flat or friction free the car will always be looking to accelerate or decelerate in the absence of input from throttle or brake. The cruise can't apply the brakes so it simply stops accelerating. When the speed drops below what's set it has to accelerate again to bring the speed back up. The faster you've set it the less noticeable it is since it takes more throttle to maintain the higher speed. So at 70 the system needs to do very little whereas at 30 it needs to make constant adjustment. The CC on my 2.5 seems to behave exactly the same as they system on the Mitsubishis and Renaults I've had thus far. I suppose it all hinges on how noticeable it is under normal use.

wutang · 11th January 2018, 15:35

Cruise on the V6 is Via an arm that operates the throttle activated by a bellows type actuator and a vacuum pump, I would hazard a guess that those experiencing pulsing or hunting could have a slight leak in the system somewhere.

Car gets up to speed pump reduces vacume closing throttle to the desired position, slight leak allows air in to system closing throttle further, pump starts up and opens throttle so car accelerates back up to speed and round you go again.

Diesel cruise is all in the ECU and involves electronic witch craft, cant help there!

My V6 cruise was always rock solid.

Regards

Richard

ryszard · 11th January 2018, 16:24

Hi,I have cruise on both my launch car and my diesel,I certainly feel the cruise cutting in on the V6,although not pulsating but certainly noticeable when it activates, whereas on the diesel it is hardly noticeable,it is much smoother and relaxed,maybe due to the torque difference.Regards Ry...

9th January 2018, 07:50	#1
TBennet Regular poster MG ZT-T 190 Join Date: Dec 2017 Location: Manchester Posts: 60 Thanks: 3 Thanked 9 Times in 7 Posts	Does everyone else's cruise control "pump" on and off? Hi there, I've owned a 190 ZT-T for a little over a month now. Do all 75s/ZTs exhibit this obvious "pumping" behaviour on cruise control where the ECU applies power for a few seconds until it's slightly over speed, then comes off the power until it's slightly under and repeats like that endlessly? Is it just MG Rover's archaic cruise control, or is mine broken? Thanks.

9th January 2018, 08:52	#5
smudge.g Gets stuck in 75 Tourer CDTi Connie SE Join Date: Jun 2017 Location: Keith, Banffshire Posts: 686 Thanks: 431 Thanked 132 Times in 105 Posts	Hi, I have a slightly older 75 but recently made great use of CC whilst driving to Norfolk from Scotland. Only noticed the increasing revs going up hills/reducing revs going downhill as already mentioned. No 'pumping' and it certainly made the journey very easy!! Good luck with solving your issue. __________________ My 75 Tourer CDTi was born Saturday, 21st June 2003 @ 09:50 My 75 was the 18,749th 75 Tourer to run off the production line, out of 27,407 It was the 195th 75 Tourer CDT Connoisseur SE (135) to be made out of 2,074 and the 1,789th 75 Tourer in Wedgewood Blue Metallic (code: JEL) to be made out of 1,871 Wedgewood Blue Metallic 75 Tourers

11th January 2018, 13:18	#8
Lord of Hog Gets stuck in Rover 75 2.5 V6 in Wedgwood Blue Join Date: Dec 2015 Location: Felbridge, East Grinstead Posts: 982 Thanks: 250 Thanked 294 Times in 206 Posts	Since roads aren't absolutely flat or friction free the car will always be looking to accelerate or decelerate in the absence of input from throttle or brake. The cruise can't apply the brakes so it simply stops accelerating. When the speed drops below what's set it has to accelerate again to bring the speed back up. The faster you've set it the less noticeable it is since it takes more throttle to maintain the higher speed. So at 70 the system needs to do very little whereas at 30 it needs to make constant adjustment. The CC on my 2.5 seems to behave exactly the same as they system on the Mitsubishis and Renaults I've had thus far. I suppose it all hinges on how noticeable it is under normal use. __________________ Conformity is not morality. Consensus is not truth.

9th January 2018, 07:53	#2
JonMs Avid contributor Rover 75 CDTi Tourer Join Date: Aug 2011 Location: Ilkley Posts: 152 Thanks: 39 Thanked 26 Times in 21 Posts	I can't say I've ever noticed that no. It doesn't sound right. On my car it's no different to the cruise on any other I've driven.

9th January 2018, 09:08	#6
SCP440 I really should get out more....... MG ZT-T 260 Join Date: Feb 2016 Location: Witney Posts: 2,504 Thanks: 6 Thanked 910 Times in 571 Posts	My ZTT is perfect on cruise but as others have said I have felt the sensation you are talking about on other makes of cars, it is usually on Turbo cars especially if they have been tweaked. The worse one I had was a Saab 9000 Aero, tweaked to about 300bhp and the cruise was almost unusable, below 60mph it was acceptable but anything above that and even passengers were complaining after a few miles. Does the Cruise get its speed input from the same source as the speedo on these cars? I know on some makes they use a different ABS Sensor for cruise than the speedo.

11th January 2018, 15:35	#9
wutang Posted a thing or two Rover 75 2.5 auto (LPG) & mg tf 160 Join Date: Nov 2006 Location: Dartford Posts: 1,124 Thanks: 5 Thanked 39 Times in 36 Posts	Cruise on the V6 is Via an arm that operates the throttle activated by a bellows type actuator and a vacuum pump, I would hazard a guess that those experiencing pulsing or hunting could have a slight leak in the system somewhere. Car gets up to speed pump reduces vacume closing throttle to the desired position, slight leak allows air in to system closing throttle further, pump starts up and opens throttle so car accelerates back up to speed and round you go again. Diesel cruise is all in the ECU and involves electronic witch craft, cant help there! My V6 cruise was always rock solid. Regards Richard

11th January 2018, 16:24	#10
ryszard Gets stuck in Moonstone diesel,X351 Jaguar and now MG ZT 260 Join Date: Dec 2013 Location: Northampton Posts: 682 Thanks: 288 Thanked 118 Times in 96 Posts	Hi,I have cruise on both my launch car and my diesel,I certainly feel the cruise cutting in on the V6,although not pulsating but certainly noticeable when it activates, whereas on the diesel it is hardly noticeable,it is much smoother and relaxed,maybe due to the torque difference.Regards Ry...