C5 rough idle when hot

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landyman
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C5 rough idle when hot

Post by landyman » 10 Jul 2015, 20:31

Hi,
I have a 2002 C5 2.2 HDi, ~160kmiles, the car runs well when cold and starts and idles fine.
As the engine warms up however the car still runs fine but it's very lumpy at idle - cylinder missing type lumpy.
There is no smoke from the back either normally, or when it's idling badly.
I guess it's not the low pressure pump as it goes like a train when my foot is down.
Also the lumpiness goes away even at low revs as soon as I put my foot down

So far I've checked

changed the MAF sensor - massively improved the performance but not the rough idle ;-/
faulty injector seals - there appears to be no leaking, no chuffing noise, no carbon deposits and it's been doing this for around 1500 miles so I imagine I'd be able to see something by now.
injector leak through test - seems they are pretty even between all the injectors, even when the engine is being lumpy - just rechecking that this evening.

where should I start next, is there any way to check the fuel pressure sensor/regulator? I had a similar problem on an old volvo and that was the cause then.

if it's not that then I guess it maybe the high pressure pump - new car time probably.

any suggestion gratefully received

Al
.

moenbeer
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Re: C5 rough idle when hot

Post by moenbeer » 10 Jul 2015, 21:07

When a car is cold, the fuel system normally add's more fuel to heat up the engine. - Could be why it's running great when cold.

I would go and change the fuelfilter first. - and if possible monitor the fuelpressurer. Don't know if one can read that out using a simple ODB thing with bluetooth connection to a smartphone?

Peter.N.
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Re: C5 rough idle when hot

Post by Peter.N. » 10 Jul 2015, 22:33

The pressure regulator on the HP pump can give a variety of problems, I have not had one cause that but they can cause difficult starting when hot and cause the engine to hunt when first started. If you can get hold of one to try it would be worth a go. Its screwed to the back of the pump with torx or allen screws and a connector.

Peter

landyman
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Re: C5 rough idle when hot

Post by landyman » 11 Jul 2015, 20:29

is there a sensor as well as a regulator?
I took the regulator out and there was a bit of dirt on it, some metal particles and some paper type stuff - guess from fuel filter.
Cleaned it up but no different to previous. I've ordered a used one to try a swap.
If there is a pressure sensor where is it (end of rail?) and do they ever go wrong?
Al

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Re: C5 rough idle when hot

Post by RustyUK » 11 Jul 2015, 21:17

There's a pressure sensor on the bottom of the fuel rail around the middle. Had to replace mine once, but that fault only caused it to go into limp home mode. If you have a lexia, or can find someone who does, I'd be looking for any error codes and watching the fuel pressure under different revs.

I'd also guess at the crankshaft or camshaft sensors. One of them might be weakening or the gap might have gotten a little too large / dirty, so the slower rotations might become less accurate to monitor.

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Re: C5 rough idle when hot

Post by Peter.N. » 12 Jul 2015, 00:26

If you have metal particles on the regulator filter your in tank pump is failing - unless its already been changed.

Peter

landyman
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Re: C5 rough idle when hot

Post by landyman » 13 Jul 2015, 08:33

not changed as far as I know, just a few tiny metal particles.
If it were that pump going wrong causing the issue wouldn't that affect the performance at high fuel consumption more than idle? Like cutting out at max wellie?
2nd hand fuel pressure regulator on the way.
If that doesn't work it may be new car time

Peter.N.
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Re: C5 rough idle when hot

Post by Peter.N. » 13 Jul 2015, 11:27

No, it probably won't affect the performance but the metal particles can damage the pump and injectors. I had this problem when I changed mine so I replaced the in tank pump. Got a secondhand one from the breakers for not to much money. This was quite a common problem when the Hdi engine first came out but most of the pumps have been replaced now.

Peter

landyman
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Re: C5 rough idle when hot

Post by landyman » 15 Jul 2015, 18:52

:(
changed the diesel filter, no difference
changed the fuel pressure regulator, no difference
changed the MAF sensor - massively improved the performance but not the rough idle ;-/
faulty injector seals - there appears to be no leaking, no chuffing noise, no carbon deposits and it's been doing this for around 1500 miles so I imagine I'd be able to see something by now.
injector leak through test - seems they are pretty even between all the injectors, even when the engine is being lumpy
tried cleaner additives - no difference
tried an italian service but that if anything seemed to make it slightly worse (drive along at 4->5k revs for a small time)

I guess all I have left is the high pressure pump, the pressure sensor on the rail, a low compression on 1 cylinder or an injector is faulty. May have to give in, save up and get a garage to have a look at it ;-(

any suggestions for anything else to try?
How easy are the injectors to remove?
Stupid question - you don't have to bleed the HDI system?
do the injectors need coding or is it a straight mechanical swap?

Peter.N.
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Re: C5 rough idle when hot

Post by Peter.N. » 15 Jul 2015, 21:08

That is an odd one, you have tried everything I would have. Cant see how the HP pump will make it run rough, its just a pump, if the pressure drops below a critical point the engine wont run. Never had a problem with injectors on the 2.0. seem to last the life of the car but I think the 16 valve ones are different.

The only thing I can think of that would be temperature sensitive would be the valve clearances, but never heard of any trouble with those although there is always a first time!

No the injectors don't need coding or bleeding.

Peter

landyman
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Re: C5 rough idle when hot

Post by landyman » 15 Jul 2015, 21:48

I'm guessing one injector is partly blocked or gone wrong in a way that doesn't show up on a leak by test, or maybe the spray pattern is rubbish. It's probably ok when there is plenty of fuel going through it (accel, or when cold) but not good enough when at idle and hot (min fuel condition).
Which injector, who knows.
There is a diesel specialist near where I'm working tomorrow so will go and ask what they reckon tomorrow

thanks
Al

Peter.N.
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Re: C5 rough idle when hot

Post by Peter.N. » 15 Jul 2015, 21:56

I was going to suggest a diesel specialist, they usually know what they are doing. If you have an injector that is not atomising properly it will usually cause a knock. Was the engine hot when you did the leak off test?

Peter

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Stickyfinger
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Re: C5 rough idle when hot

Post by Stickyfinger » 15 Jul 2015, 21:58

Have you tried an Injector Cleaner additive, I have had good results with it before with a rough engine after using Supermarket petrol for too long.

landyman
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Re: C5 rough idle when hot

Post by landyman » 23 Jul 2015, 21:14

ok, update, I had a really good look and there was some carbon around the left cylinder' injector. I took that one out (easier said than done but getting the engine really hot 1st helps a lot), cleaned up the tar and cut a new seat with a tool, fitted a new washer and replaced the injector with a 2nd hand one from ebay. Not sure of the tension the hold down nuts should be but I'm guessing I did about 10NM (1 metre long bar and pull 1kg). It no longer appears to leak anyway.
It now seems to be a bit better - it still idles rough but not as bad and only when the air con is on (which pulls the revs down a bit). I can't see any other leaks (put washing liquid solution around them and no bubbles when medium hot). May try this again tomorrow after a long drive when really hot to see if any of the others are leaking.

How tight should the injector clamp bolts be?
I'll try more cleaner and a longer drive tomorrow

Al.

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darbuck
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Re: C5 rough idle when hot

Post by darbuck » 24 Jul 2015, 08:47

anytime i had that kind of trouble with diesels when i was taxiing iused to trow a fiver of kerosene in its better than the shp bought additives