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2007 C6 - "juddering" under light acceleration
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Okaimoo   
Tue Mar 18 2014, 07:39pm
Joined: Mar 08 2014
Member No: #1618
Location: United Kingdom
 Hi,

I recently purchased a 2007 Citroen C6 exclusive, which is certainly a very beautiful car and very comfortable. However I have an issue with it which I am rather concerned about. If you put your foot down the car changes gear smoothly and accelerates as you would expect (though there does seem to be a whine from the turbo?). However under light acceleration holding a fairly constant speed (pretty much any speed, but I can recreate easily at about 35) the car feels like it's coughing or jumping, you feel the power drop off then kick back in (without any movement on the pedals).

The only thing I've seen before is a very old BMW with a half dead gearbox where it took a long time to shift, so you'd put your foot down and suddenly it would jump into gear and you'd get a sharp jolt - it's not that severe, but it is very noticeable.

This seems to be much more pronounced in "Sport" mode, but is present irrespective. I don't think it's the gearbox shifting up/down in the usual way because it isn't really appreciable all the time, and it does it if I put the gearbox into the "semi automatic" transmission mode.

Does anyone have any thoughts about what might be causing it or what to look for? Any advice would be really gratefully received. Thanks Dale
C6Dave   
Wed Mar 19 2014, 07:35am

Joined: Oct 01 2009
Member No: #1
Location: Northumberland
 1st thing to do is change the transmission fluid if you suspect it is gearbox related, there are posts on how to do it.

However it may also be a sticking EGR valve which gives similar symptoms.
Website
Hattershaun   
Wed Mar 19 2014, 05:52pm
Joined: Dec 19 2010
Member No: #320
Location: Bedfordshire, UK
 I had similar symptoms always at approx 1700rpm.
It was a faulty EGR valve.
Jodyone   
Wed Mar 19 2014, 06:17pm
Joined: Mar 24 2013
Member No: #1240
Location: Cornwall
 My car is similar, I've been meaning to post on it but may as well report here. Between 1700-1900rpm, light throttle, any gear, it hunts until I change the throttle position (not always practical). It's got steadily worse over 25K miles from occasional to consistent. From reading here, I suspect the EGR valves first, but Lexia doesn't report any faults and an actuator test works fine. It had a new fuel filter not long ago which didn't noticeably change anything.

Has anybody successfully removed and cleaned the front valve? (I know the back one is trickier..!). I've read the workshop page on it that Dave's kindly hosting, but I see there's a coolant pipe going to a heat exchanger- does it need a coolant drain to do the job?! (doesn't mention it on the manual).

I also have an occasional "depollution system faulty" alert (like half the board membership, it seems), which is getting a little more common (twice in a month). I haven't managed to catch it at home to put a Lexia on it though before it clears. Related?!
travlician   
Wed Mar 19 2014, 07:07pm
Joined: Jan 22 2011
Member No: #350
Location: Paradera
 Jodyone,
I needed to drain the cooling system to replace the front EGR valve. You may find a thread I initiated somewhere on this forum. Strange you have nothing in Lexia as a "depolution system faulty" message should leave an entry in the fault log. I had a message in Lexia about inconsistency between the air mass flow sensors when my EGR valve was faulty. Testing it with Lexia did not generate a message in Lexia but you need to listen to the EGR valves as they are being actuated and I heard hesitation on the front EGR valve before I replaced it.
Jodyone   
Wed Mar 19 2014, 07:31pm
Joined: Mar 24 2013
Member No: #1240
Location: Cornwall
travlician wrote ...

Jodyone,
I needed to drain the cooling system to replace the front EGR valve. You may find a thread I initiated somewhere on this forum. Strange you have nothing in Lexia as a "depolution system faulty" message should leave an entry in the fault log. I had a message in Lexia about inconsistency between the air mass flow sensors when my EGR valve was faulty. Testing it with Lexia did not generate a message in Lexia but you need to listen to the EGR valves as they are being actuated and I heard hesitation on the front EGR valve before I replaced it.

Travlician,

Thankyou, that's interesting to know. Annoyingly, one of the standing errors I do get is with the fault log itself! Which may not be helping. Also, I may be missing something - it's taken some mind-bending for me to get my head around the temperamental Lexia software altogether.

I did listen to the valves as you describe, they both sounded fine (similar) as far as I could tell, but I'll do it again anyway to listen for any hesitation. When you removed the front valve, did you consider cleaning/reconditioning it, or is replacement the only practical option?
Okaimoo   
Thu Mar 20 2014, 09:18pm
Joined: Mar 08 2014
Member No: #1618
Location: United Kingdom
 Thanks for the suggestions, I have had it looked by a fairly generalist local garage and they have said currently no fault codes, but suspect either EGR valve or maybe transmission fluid.
The garage I bought it from has it booked into a specialist next Monday so hopefully they'll be able to dig into it a little more. Thanks again for all the help. I've been reading the threads on the cruise control button not working and have found the "jiggling the steering wheel and/or hitting it" approach fixes my issues too! This forum really is a life saver.
travlician   
Fri Mar 21 2014, 01:29am
Joined: Jan 22 2011
Member No: #350
Location: Paradera
 About cleaning or replacing the EGR valve: Since I live on an island and the fastest way to get C6 parts take about 3 weeks, I decided to buy the EGR valve before taking the failed one out (I did use perforated plates to limit airflow through the EGR valves which worked OK, no more error messages but knowing it's not as it should be). After the replacement I took the failed EGR valve apart and found a carbon ring that indicates the position of the valve to be broken, so cleaning would not have helped, but I can imagine other EGR valves failed for other reasons and might therefore behave differently when tested with Lexia.
Jodyone   
Fri Mar 21 2014, 04:10pm
Joined: Mar 24 2013
Member No: #1240
Location: Cornwall
 Thanks for that travlician. I'm going to leave everything as is for the moment, it just isn't a big enough problem for me to get involved in a fiddly dismantling job. I may rue that decision later in the year when I don't have any time and I'm doing 800 miles a week! I'm doing the brake pads, brake fluid replacement, new oil and filter (and may as well get a new fuel filter) next week though, so I'll see if that drums up some enthusiasm for the job..!

Okaimoo- I endured the cruise control thing for months, and eventually got fed up of moving the steering wheel every third journey. Last year I took the plastic cowling off the underneath of the steering column (one deep Torx screw), fiddled around with/reseated the wires thus exposed, and it's been fine ever since! About 10 minutes work including hunting around for a long enough bit holder.
gmerry   
Fri Mar 21 2014, 04:52pm
Joined: Dec 11 2009
Member No: #21
Location: Scotland
 Hi Jodyone, when changing the brake fluid make sure you displace the trapped fluid in the calipers (this is the likely to be the fluid in the worst condition) but don't displace it back to the ABS block or you risk wrecking that component.

Regards
G
Jodyone   
Fri Mar 21 2014, 06:29pm
Joined: Mar 24 2013
Member No: #1240
Location: Cornwall
gmerry wrote ...

Hi Jodyone, when changing the brake fluid make sure you displace the trapped fluid in the calipers (this is the likely to be the fluid in the worst condition) but don't displace it back to the ABS block or you risk wrecking that component.

Regards
G


Thanks gmerry. I'm planning to follow your excellent guide on this site, using wooden blocks in place of the pads to make sure the callipers are drained fully. However, does pushing the cylinders fully back risk pushing the trapped fluid back up the line? As long as that's done with the bleed screws open so the fluid flows out rather than up the line, should everything be ok?
 

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