C5 "hunting"

[Gary180259]

Hi there people.

 

I am new to this forum and I was wondering if anyone could help with my problem. I am no mechanic but I will give you as much info as I can.

 

My car is a 2007 C5 2.0 HDi (136) Auto Exclusive Diesel

 

This is my 3rd C5 and I love 'em and until now I have had very few problems, however I have one now! I can only desribe the fault as a "hunting" or "pulsing" of the engine. it's like it can't decide what to do. The engine pulses every couple of seconds with a variation of about 200 rpm. It happens under light acceleration and also sometimes when I am just trying to maintain a constant speed. Incidentally, it doesn't happen when the cruise control is on.

 

here is what my mechanic has done thus far... A thorough clean of the EGR valve and the inlet manifold. Replaced the throttle body and the throttle position sensor. This has made no difference except that now I have a warning... "Depollution System Faulty" and the engine managment light comes on and stays on. He has now regenerated the DPF filter. This took two attempts but now gives a 97% clear reading on their computer thingy. However, this was to no avail and the warning and management light are still on.

 

Also the automatic gearbox fluid has been changed and topped up. (It was a little low)

 

it doesn't seem to affected MPG... she is still returning 45mpg running back and forth to work down coutry lanes and in traffic, which I think is pretty good.

 

So there we have it, any ideas guys?

 

Thanks,

 

Gary

[paul.h]

Welcome to the forum.

 

If the depollution warning is given and the engine management light is on there will be a fault code and freeze frame data when the fault occurred which will give a good idea of what is wrong. So you should have the fault codes read. There are many things that could be wrong such as the air flow meter or a lambda sensor. If you just try replacing parts without checking the fault code you could waste a lot of money before finding the actual fault.

[Randombloke]

 

This is my 3rd C5 and I love 'em and until now I have had very few problems, however I have one now! I can only desribe the fault as a "hunting" or "pulsing" of the engine. it's like it can't decide what to do. The engine pulses every couple of seconds with a variation of about 200 rpm. It happens under light acceleration and also sometimes when I am just trying to maintain a constant speed. Incidentally, it doesn't happen when the cruise control is on.

 

 

The fact it doesn't happen when the cruise control is on says to me that there is a worn spot on the accelerator potentiometer (throttle position sensor) where it gives intermittent changes in the resistance reading, or a loose wire. You've replaced the pot so maybe a loose wire or dirty contacts.

 

Might be worth putting a resistance meter across the old throttle pot and measuring, and seeing if there is a point where the resistance reading jumps about. 

 

Worth finding out if the new throttle pot needs to be coded into the vehicle, I know with things like EGR valves a new one requires coding into the vehicle, until that's been done, diagnostic messages aplenty. 

 

Worth also checking the battery voltage....

[Gary180259]

Thanks guys, I will print this off and give it to my mechanic who has been excellent so far.

 

He has only charged me £200 which includes auto box fluid and many hours of labour.

 

any more ideas will be welcome, i will keep you posted.

 

Cheers

 

Gary

[coastline taxis]

1st

Tell him to go to live data with his diagnostic equip then straight into injection adaptation and see what the 4 injectors are doing.

2nd

check all your air/vacum pipes for leaks/splits.

3rd

do as paul suggested and post the fault codes on here then you can get a more specific answer

[Gary180259]

Hi guys,

 

I don't seem to be getting very far with my problem. Very frustrating.

 

Aparrently, my mechanic has checked all your suggestions... Every time they seem to cure the problem, it comes back with a vengeance. Hopefully on Monday I will get a list of all the fault codes that have come up, so I will let you know as soon as I can.

 

In the meantime, thanks for your help so far. I really want to get this sorted because the car is an absolute dream to drive otherwise! :rolleyes:

[slugworth1987]

Mines started doing this aswell

[Gary180259]

Hello people,

 

Sorry I didn't get back earlier, I have been in hospital.

 

Anyway, today I had my car booked into an Auto Tech place a few mies from where I live. I couldn't get my hands on the fault codes as the mechanic "chucked them out"!

 

Never mind, I told the Auto Tech guys as much as I could and low and behold... I think they have cured it!!! They couldn't get any fault codes to come up... they blanked off the EGR valve and I think it's sorted. No pulsing, no hesitation, she goes like a dream.

 

So there we are... I have spent £400 on trying to sort this out and it seems it was a fairly simple fix (fingers crossed)

 

Slugworth, don't waste loads of money, just get the EGR valve blanked off!! I hope it works for you :)

[slugworth1987]

ill get it out and give it a good clean first before i blank it off, need to check the swirl valve on mine aswell so gives me an excuse to pull it apart HAHA!!! thanks for the update!

[iulian.arg]

Hello,

 

I might have found the cause and the solution to this problem.

 

Description first:

- I have a C5 2007 2.0HDi RHR 100Kw 6 speed auto with 150k km. 

- 4 years ago I encountered first this hunting and pulsing behavior that is extremely visible especially in vehicles with auto boxes due to torque converter "unlock" way of functioning.

- the pulsing was present only in warm weather and from time to time.

- the pulsing appeared between 1500-2000 rpm.

- the pulsing was present even with the gearbox in M but less visible.

 

What I've done to try to get rid of the problem:

- cleaned the intake manifold - no change at all.

- changed the EGR valve with original Delphi part - no change at all.

 

What actually solved the problem:

- I unmounted and sent the particle filter to a professional cleaning center because of frequent regenerations (<100-150km) and because the back-pressure made by the particle filter on the road in full throttle was in the 800s millibars which was huge (determined with Lexia).

- after the cleaning the pulsing problem didn't appeared ever again in about 5k km and 2+ months of warm weather.

- the back-pressure is now under 100 mbar even in full throttle and the regeneration interval is between 600-800 km.

 

My interpretations and observations:

- the pulsing appeared for some reason only in warm weather.

- the pulsing appeared only before a regeneration but not in the immediate proximity and not as a sign of imminence.

- the pulsing didn't appeared a period after the regeneration

- my estimation is that the pulsing appeared in the last third of the interval between 2 regenerations when the particle filter was pretty clogged.

- EGR blanking solves the problem but I don't think it's the cure of it.

- my though is that this EGR design is pretty flawless and it should last several hundred thousand km; the pulsing is actually a sign of a good EGR; my old EGR only had a slight dust of diesel soot inside and had a perfect movement.

- the cleaning costed me ~60 euros; the procedures took ~24 hours of high temperatures and air flow in a industrial grade furnace.

 

A funny fact was that I remembered that I had the problem in the past only recently when I saw my old EGR on a shelve  ^_^. That's when I realized that the DPF cleaning solved my pulsing problem and then I decided to come here and expose my experience with this problem.

 

Hope that my experience helps others.

 

Here's the DPF before and after the cleaning. Don't think one needs indications which is which  :rolleyes:.

Edited June 27, 2018 by iulian.arg

[paul.h]

Thank you for your help with this topic, your experience may benefit a lot of other people.