Cruise disengaging on resume.

Brendan W · Dec 7th, 2016, 11:43

Just wondering if anyone has seen this.
Two hour trip in the wee hours mainly motorway and dual carriageway.
Cruise set to 100kph. Hit the disengage button early to slow for the 60kph limits and hit resume on exit still in top gear.
Twice the car failed to reach the set speed and fell away just before the set point. Hit the resume again and it picked up.
No lights or other signs. Isolated incident. Nothing in the ten days since.
Might have imagined it but the tacho and speedo seemed to be briefly out of sync and it had a feel of clutch slip about it.
Original clutch and third CPS.

cheshired5 · Dec 7th, 2016, 12:13

Ok, well here's my theory.

60kph is a pretty slow speed for 5th gear which would result in low rpm.....below the main torque curve.
Your VNT mechanism would need to be in fine fettle to make the fine adjustments to harness the low exhaust flow and maybe VNT wasn't adjusting as designed so the turbo was struggling to make boost.
As engine speed increased, maybe the VNT couldn't adjust again to harness this and boost tailed off before your desired speed.
The VNT has since freed itself and is now ok.....

Cruise may be a red herring so I'd try doing the same acceleration manually with cruise off.
It would be fairly laboured I imagine.

Brendan W · Dec 7th, 2016, 14:52

I'll try that but I'll probably be lighter of foot than the cruise.
Would have thought the cruise would back off and not lug the motor.

Rossi-fan · Dec 7th, 2016, 16:23

As above. I don't think the cruise would have picked up to the set speed in your manual car. Had it been an Auto, it probably would have Brendan.

Brendan W · Dec 7th, 2016, 16:41

These manuals are so much work

V70Zig · Dec 7th, 2016, 16:47

That's why I love my auto....press resume and it'll drop down gears then change up as the speed increases. Don't love the MPG, but I can live with that.

Brendan W · Jul 13th, 2018, 18:17

Looks like it was clutch slip after all. Happening nearly once a month now if you force things below 2000rpm.
Don't get much warning with these cars do you ?

petey · Jul 14th, 2018, 07:02

The ECU knows what gear it’s in by matching road speed to engine speed. If when you’re in cruise and you just knock it out of gear when the transmission is unloaded, (which is the same as 100% clutch slip), the cruise will disengage as soon as there’s a disparity between the measured road speed and the engine speed. This is because the car can no longer determine what gear it’s in and for safety, it reasons that it’s unikely to be good to persist maintaining a speed when it could be the speed detection process that’s failed.
This is why fitting a 6 speed box to a 5 speed car might work but some elements will not.
Clutch slip would (and should) stop cruise control working.

Dec 7th, 2016, 11:43	#1
Brendan W Premier Member Last Online: Apr 2nd, 2024 19:50 Join Date: Dec 2007 Location: Wexford	Cruise disengaging on resume. Just wondering if anyone has seen this. Two hour trip in the wee hours mainly motorway and dual carriageway. Cruise set to 100kph. Hit the disengage button early to slow for the 60kph limits and hit resume on exit still in top gear. Twice the car failed to reach the set speed and fell away just before the set point. Hit the resume again and it picked up. No lights or other signs. Isolated incident. Nothing in the ten days since. Might have imagined it but the tacho and speedo seemed to be briefly out of sync and it had a feel of clutch slip about it. Original clutch and third CPS.

Dec 7th, 2016, 12:13	#2
cheshired5 Premier Member Last Online: Dec 26th, 2021 13:42 Join Date: Dec 2013 Location: Crewe	Ok, well here's my theory. 60kph is a pretty slow speed for 5th gear which would result in low rpm.....below the main torque curve. Your VNT mechanism would need to be in fine fettle to make the fine adjustments to harness the low exhaust flow and maybe VNT wasn't adjusting as designed so the turbo was struggling to make boost. As engine speed increased, maybe the VNT couldn't adjust again to harness this and boost tailed off before your desired speed. The VNT has since freed itself and is now ok..... Cruise may be a red herring so I'd try doing the same acceleration manually with cruise off. It would be fairly laboured I imagine. __________________ 2002 S60 SE D5 Manual 209000 miles

Dec 7th, 2016, 16:23	#4
Rossi-fan Premier Member Last Online: Feb 12th, 2023 10:07 Join Date: May 2009 Location: Durham	As above. I don't think the cruise would have picked up to the set speed in your manual car. Had it been an Auto, it probably would have Brendan. __________________

Dec 7th, 2016, 16:47	#6
V70Zig Master Member Last Online: Apr 10th, 2024 16:20 Join Date: Sep 2012 Location: Loughborough	That's why I love my auto....press resume and it'll drop down gears then change up as the speed increases. Don't love the MPG, but I can live with that. __________________ 2008 V70 SE D5 Auto 185 ...now 205 Volvo Polestar......190k Passed away - 1999 V70 2.5tdi Auto 340632 miles, RIP.

Dec 7th, 2016, 14:52	#3
Brendan W Premier Member Last Online: Apr 2nd, 2024 19:50 Join Date: Dec 2007 Location: Wexford	I'll try that but I'll probably be lighter of foot than the cruise. Would have thought the cruise would back off and not lug the motor.

Dec 7th, 2016, 16:41	#5
Brendan W Premier Member Last Online: Apr 2nd, 2024 19:50 Join Date: Dec 2007 Location: Wexford	These manuals are so much work

Jul 13th, 2018, 18:17	#7
Brendan W Premier Member Last Online: Apr 2nd, 2024 19:50 Join Date: Dec 2007 Location: Wexford	Looks like it was clutch slip after all. Happening nearly once a month now if you force things below 2000rpm. Don't get much warning with these cars do you ?

Jul 14th, 2018, 07:02	#8
petey Master Member Last Online: Sep 11th, 2023 13:10 Join Date: May 2009 Location: Chippenham	The ECU knows what gear it’s in by matching road speed to engine speed. If when you’re in cruise and you just knock it out of gear when the transmission is unloaded, (which is the same as 100% clutch slip), the cruise will disengage as soon as there’s a disparity between the measured road speed and the engine speed. This is because the car can no longer determine what gear it’s in and for safety, it reasons that it’s unikely to be good to persist maintaining a speed when it could be the speed detection process that’s failed. This is why fitting a 6 speed box to a 5 speed car might work but some elements will not. Clutch slip would (and should) stop cruise control working.

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