Cruise control surging

AP90 · Feb 6, 2015

Hi

Pottering along at 50mph last night using the cruise control

For no reason the engine suddenly surged from about 2000 rpm to 4500 rpm

It dropped down again but then surged again to nearly 5000 rpm so I trod on the brake to stop the CC

Any ideas what could cause this?

It's a 2001 2.5 Diesel

I dod do a search but nothing similar found

Many thanks

Bladerunner919 · Feb 6, 2015

Are you sure it didn't just change down a gear? Were you on a level road or an incline?

I'm assuming your speed didn't double as the revs doubled!

AP90 · Feb 6, 2015

Bladerunner919 said:
Are you sure it didn't just change down a gear? Were you on a level road or an incline?

I'm assuming your speed didn't double as the revs doubled!

Yes sorry on level ground, very slight increase in speed but the event was over fairly quickly. A bit disconcerting........

Datatek · Feb 6, 2015

AP90 said:
Yes sorry on level ground, very slight increase in speed but the event was over fairly quickly. A bit disconcerting........

Sounds like it just down shifted for some reason, Strong headwind?
CC is electronic via the EDC on the diesel.

quavey · Feb 6, 2015

It must have the ability to sense the speed of the car, it sounds like it lost the feed from the sensor and so assumed the car had slowed dramatically therefore its attempted to accelerate rapidly.

As a side to this, I don't use mine alot as it generally hunts around the set speed say 60mph but it will drop to 58mph before pulling back to 60/61. I'm assuming this isnt how they were from factory and its a leak in my admittedly bodged vacuum hoses, unless this hunting is normal?

AP90 · Feb 6, 2015

Datatek said:
Sounds like it just down shifted for some reason, Strong headwind?
CC is electronic via the EDC on the diesel.

Hi Keith

No noting like that, the CC on this car has always worked really well, so that's why this is all bit weird.

I have had some mechanical work done on the car recently, transfer box replaced etc but no fiddling with the electronics so I'm a bit mystified.

It was all going so well.......

wammers · Feb 6, 2015

quavey said:
It must have the ability to sense the speed of the car, it sounds like it lost the feed from the sensor and so assumed the car had slowed dramatically therefore its attempted to accelerate rapidly.

As a side to this, I don't use mine alot as it generally hunts around the set speed say 60mph but it will drop to 58mph before pulling back to 60/61. I'm assuming this isnt how they were from factory and its a leak in my admittedly bodged vacuum hoses, unless this hunting is normal?

Different system on the diesels no vacuum involved. CC on diesels is fly by wire. OPs car will be dropping a gear because the engine ECU thinks the engine is under load. Diag may show something up.

AP90 · Feb 6, 2015

quavey said:
It must have the ability to sense the speed of the car, it sounds like it lost the feed from the sensor and so assumed the car had slowed dramatically therefore its attempted to accelerate rapidly.

As a side to this, I don't use mine alot as it generally hunts around the set speed say 60mph but it will drop to 58mph before pulling back to 60/61. I'm assuming this isnt how they were from factory and its a leak in my admittedly bodged vacuum hoses, unless this hunting is normal?

Yes that's about it, I use the CC a lot actually and this is the first time it's played up

AP90 · Feb 6, 2015

wammers said:
Different system on the diesels no vacuum involved. CC on diesels is fly by wire. OPs car will be dropping a gear because the engine ECU thinks the engine is under load. Diag may show something up.

Didn't feel like dropping a cog, more like 2 if you know what I mean, it was a really unusual surge

wammers · Feb 6, 2015

AP90 said:
Didn't feel like dropping a cog, more like 2 if you know what I mean, it was a really unusual surge

If you are at 50 MPH car will be in torque lock 4th gear. If it dropped to 3rd that would give you what you had. It is effectively dropping two gears. You may want to check the oil level in the box just to be on the safe side.

AP90 · Feb 6, 2015

wammers said:
If you are at 50 MPH car will be in torque lock 4th gear. If it dropped to 3rd that would give you what you had. It is effectively dropping two gears. You may want to check the oil level in the box just to be on the safe side.

Great, thanks of the explanation, I had the ATF and filter changed changed last week by my specialist so pretty sure that's ok, one of the issues of not doing stuff myself I suppose

wammers · Feb 6, 2015

AP90 said:
Great, thanks of the explanation, I had the ATF and filter changed changed last week by my specialist so pretty sure that's ok, one of the issues of not doing stuff myself I suppose

Maybe you need to take it back to your specialist and tell him what happened. Maybe a connection, maybe not, but best to have them take a look.

AP90 · Feb 18, 2015

Sorry, just to close this thread.........I had it in 3 instead of D.........what a numpty!!

The old P38 paranoia creeping in.........apologies and thanks

Datatek · Feb 18, 2015

AP90 said:
Sorry, just to close this thread.........I had it in 3 instead of D.........what a numpty!!

The old P38 paranoia creeping in.........apologies and thanks

:clap2: Brave man to admit it

AP90 · Feb 18, 2015

And a very stupid man to do it.........

Mark you, the only caveat was that it was 00:45 after a hard days work,.... it certainly livened me up a bit!!

Cruise control surging

AP90

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Bladerunner919

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AP90

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Datatek

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quavey

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AP90

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wammers

No longer with us, RIP

AP90

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AP90

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wammers

No longer with us, RIP

AP90

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wammers

No longer with us, RIP

AP90

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Datatek

Well-Known Member

AP90

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