Xantia V6 running rich.

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Allmostfrench
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Xantia V6 running rich.

Post by Allmostfrench »

Hi folks, recently had the timing belts etc changed by a reputable Citroen shop in another State that I can't return to due to COVID....

The engine now has a slight whistling noise between 1-3k rpm. Would this be the new belts being too tight?

I mention the noise because the inlet manifold has been off to change the plugs, and I wondered if it was an air leak?

The car starts and idles fine, but has a "rich stumble" as soon as you accelerate.
More throttle will see the the car smooth out and accelerate without missing.

It is using more fuel than normal, and the tail pipe is sooty.

I'm assuming that this engine uses a TPS and MAP sensor to determine fuel needs.

Where is the MAP sensor? I wonder if it has become disconnected electrically or vacuum pipe.

There is no fault showing on the dash, and I don't have ready access to LEXIA.

Any bright ideas most welcome. This car usually runs really well getting 8lit/100km.

Thanks in advance, Chris.

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xantia_v6
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Re: Xantia V6 running rich.

Post by xantia_v6 »

Allmostfrench wrote:
16 Jul 2020, 07:54
The engine now has a slight whistling noise between 1-3k rpm. Would this be the new belts being too tight?
The aux belt can't be over-tightened, the tensioner is fully automatic.

The timing belt tensioner is a different story. The original timing belt tensioner on the ES9J4 engine was a static tensioner which was very fussy about adjustment and officially requires a SEEM gauge to set the tension. In late 1999 the tensioner design changed to a semi-automatic design that is more tolerant to mis-adjustment. The early type of tensioner was no longer supplied as a spare, so any car that has had the tensioner replaced will have the later type.

It is however possible to over-tension the later type if you really muck up the procedure, I have done it myself (although it was due to a badly made chinese tensioner), and that did cause the timing belt to whine.
Allmostfrench wrote:
16 Jul 2020, 07:54

I mention the noise because the inlet manifold has been off to change the plugs, and I wondered if it was an air leak?.
Also possible.
Allmostfrench wrote:
16 Jul 2020, 07:54
The car starts and idles fine, but has a "rich stumble" as soon as you accelerate.
More throttle will see the the car smooth out and accelerate without missing.

It is using more fuel than normal, and the tail pipe is sooty.

I'm assuming that this engine uses a TPS and MAP sensor to determine fuel needs.

Where is the MAP sensor? I wonder if it has become disconnected electrically or vacuum pipe.
The map sensor is attached to the rear face of the inlet manifold. Check that the plug has been attached. There may also be an additional port on the rear face of the manifold blannked off with a rubber cap. If the cap is split or missing, there will be a significant vacuum leak. The extra port is not present on later engines.

There is also a vacuum pipe from the manifold to the fuel pressure regulator at the timing belt end of the engine. if this hose is not connected, the engine will run rather rich.

One more thing... try disconnecting the battery to reset the engine ECU, I have had them go into a strange mode which was fixed by a reset.

Allmostfrench
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Re: Xantia V6 running rich.

Post by Allmostfrench »

Thanks for all of that!
When it stops raining (yes, even in Australia!) I will check it all out.
I'm a bit concerned about the cam belt being over-tensioned and causing the water pump bearing or tensioner bearing to fail.
I might have to take it to someone else to have the tension re-checked.
Thanks for the quick reply, I'll let you know how I go.

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Re: Xantia V6 running rich.

Post by Allmostfrench »

A quick update:
Took it to my local French Car shop and they could not get it to throw any codes....
And now it seems to be behaving itself most of the time!
I wonder if there might be a bad connection to the MAP sensor, or can they play up from time to time?
They pointed out that the coil packs had some cracks in the epoxy that they are potted in, although the car doesn't miss under load.
They reckoned that the whistle wasn't too loud and was just sounding different to the old belt that was worn and possibly a bit loose.
Is replacing the MAP sensor and coil packs on a 20 year-old car probably a good idea anyway? I just love driving this car!
Thanks for the suggestions so far.

zs&tas
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Re: Xantia V6 running rich.

Post by zs&tas »

Hi 👋 I am surprised that you had no codes if running rich ? The O2 sensor should pick that up ? , The O2 sensor would also effect the cars running . If it was my car , I would change the coil packs , even of it is " running ok " you wouldn't believe a difference they make ! The engine will be much happier and smoother. With out hearing the noises it's hard to tell what that is ? If the intakes been off I'd check everything to do with it to make sure everything is connected and torqued up , I've had intake leaks on a different engine before , couldn't for the life of me work it out , I just decided to nip up the manifold and suddenly it was fixed !

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Re: Xantia V6 running rich.

Post by Allmostfrench »

Thanks to those that replied - it's all part of the picture!
Fitted a new MAP sensor today and it is a bit smoother but it wants to rev up and down if you just crack the throttle open in neutral to hold the revs at about 1500 rpm.
It goes from 1500-2000 in a regular fashion, sort of what I imagine the "Lambda Dither" would do as it regulates the mixture on light throttle openings.
Could it be the O2 sensor? Still no codes thrown although they have a fancy Bosch machine rather than a PSA one. Still, it's a Bosch system.....
When you start it up, it idles smoothly at about 850 rpm hot or cold, so the ISV seems to be operating OK.
Any other brainwaves?

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xantia_v6
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Re: Xantia V6 running rich.

Post by xantia_v6 »

Is the throttle position sensor giving sensible readings? and the MAP sensor for that matter?

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Mandrake
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Re: Xantia V6 running rich.

Post by Mandrake »

Allmostfrench wrote:
16 Jul 2020, 07:54
Hi folks, recently had the timing belts etc changed by a reputable Citroen shop in another State that I can't return to due to COVID....

The engine now has a slight whistling noise between 1-3k rpm. Would this be the new belts being too tight?

I mention the noise because the inlet manifold has been off to change the plugs, and I wondered if it was an air leak?
Is the whistling noise constant in that rpm range or does it increase with throttle and go away when you ease off slightly ?

If so it's an air leak in the intake system. Since the inlet manifold has come off it could be a leak in the paper gasket, (did they replace it ? It's single use...also it's possible to damage it when fitting it if not careful) or the small hose to the pressure regulator on the left hand side, or the blanked off spigot at the rear.

Another source of inlet whistle which my car has had trouble with (and which I have never been able to 100% cure) is an air leak on the air filter box. Check that the air filter box lid hasn't been put on improperly and taken a chunk out of a corner of the air filter rubber gasket... quite easy to do by mistake.

It can be quite fiddly to get the air filter box lit to fit properly and seal around the edge of the filter, especially when they get old and warped from heat - if they have rushed the reassembly and not made sure it's seated properly before tightening the screws it can sometimes leak.

Check the rubber hose at the back that goes to the throttle body and its two hose clamps. Also check the smaller one which goes to the idle compensation valve. This smaller hose doesn't seem to come with a hose clamp (at least neither of my V6's came with one!) but I found it leaks there if not clamped, so fit a jubilee clamp to that hose as well, and while you're at it make sure the air temperature sensor which inserts in the side of that small spigot isn't falling out as that is yet another possible source of air leak that will whistle.

Mine used to whistle like crazy when I first got it in the 2k-3k rev range under throttle and while it still makes a slight noise I've managed to get rid of most of the noise by fixing all the air leaks around the air filter box.
The car starts and idles fine, but has a "rich stumble" as soon as you accelerate.
More throttle will see the the car smooth out and accelerate without missing.
I doubt it's a rich stumble. Much more likely to be a lean stumble! When you open the throttle quickly on a petrol car with a mechanical throttle plate the natural inclination is for the mixture to go very lean for a moment, so the car has to pump in a lot of extra fuel to minimise this.

There are two primary inputs which dictate the fuel injection ratio - the MAP sensor and the throttle position sensor. (With secondary input from the crank position sensor giving engine rpm, the air temperature sensor and coolant temperature sensors)

MAP sensors are slow to respond so it's the job of the throttle position sensor to detect that sudden snap open of the throttle and inform the ECU that it needs to inject lots of fuel NOW to prevent a lean stumble. If the throttle position sensor is dirty or faulty in some way you could experience severe stumbles whenever you suddenly open the throttle.

So the throttle position sensor is a possible candidate for your stumble.
It is using more fuel than normal, and the tail pipe is sooty.

I'm assuming that this engine uses a TPS and MAP sensor to determine fuel needs.
More fuel and sooty tail pipe could be a few things...

Misfire under load (ignition problem)
Faulty map sensor (the car runs rich if the map sensor isn't working and it has to rely on the throttle position sensor only)
faulty oxygen sensor. (The car runs rich all the time if the oxygen sensor is faulty)

If it really is running rich then don't drive it too much or too hard until repaired or you could do permanent damage to the catalytic converter.

Allmostfrench
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Re: Xantia V6 running rich.

Post by Allmostfrench »

Thanks chaps!
I'll follow all of that up.
I'm pretty sure that the whistle is a mechanical thing, but will check all the areas suggested.
I'm wondering if there might be a dodgy part of the TPS as that is the bit that would get the most use.

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Mandrake
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Re: Xantia V6 running rich.

Post by Mandrake »

Allmostfrench wrote:
11 Sep 2020, 10:56
Thanks to those that replied - it's all part of the picture!
Fitted a new MAP sensor today and it is a bit smoother but it wants to rev up and down if you just crack the throttle open in neutral to hold the revs at about 1500 rpm.
It goes from 1500-2000 in a regular fashion, sort of what I imagine the "Lambda Dither" would do as it regulates the mixture on light throttle openings.
Could it be the O2 sensor? Still no codes thrown although they have a fancy Bosch machine rather than a PSA one. Still, it's a Bosch system.....
When you start it up, it idles smoothly at about 850 rpm hot or cold, so the ISV seems to be operating OK.
Any other brainwaves?
This engine is notorious for worn and clogged up idle compensation valves.

They can get clogged completely with carbon and soot so they can't move - when that happens the car will have a tendency to stall when you come to a stop and the revs dip below normal idle. My second V6 had this problem when I first got it and I had to take it out and thoroughly clean it.

Unfortunately that can sometimes reveal problem number two - slack bearings in the valve that let it wobble around a bit. If it has that issue it will usually idle steady once settled but constantly wobble up and down if you try to hold it at 1500 rpm. This is because it has a lot of rotational inertia (the valve rotates) but if there is no friction to damp its movement it tends to keep overshooting the mark and over compensating leading to a constant oscillation.

A large fluctuation in RPM at that speed is unlikely to be the oxygen sensor but is probably the idle compensation valve, so it may be worth taking it off and cleaning inside it.

The idle compensation valve is a rotational solenoid type, and unlike a stepper motor idle compensation valve it also operates at higher throttle openings - the ECU commands it to fully open when you put your foot down and then to close again when you're nearing idle. So it is constantly adjusting as you drive, like a small ECU controlled throttle valve, not just setting the idle speed.

Another thing that can cause the idle compensation valve not to regulate well when you've got a slight amount of throttle is if there is no leakage past the throttle butterfly due to it being dirty.

When a throttle butterfly is clean there is a small deliberate amount of leakage past the edge which contributes to the idle air flow, and the system is designed to expect that.

However if its dirty it forms a complete seal at the edge when closed and forces the idle compensation valve to open more than normal to maintain idle, and furthermore it doesn't allow any air through until it is significantly open - effectively it adds some dead band to the bottom of the throttle range where the ECU detects the throttle position sensor moving but the airflow doesn't increase. This can also cause a slight stumble.

If the throttle butterfly looks dirty or gummy around the edge definitely clean it.

If you have a Lexia - which I know you don't, you can check the idle compensation valve open percentage and it should be around 25-30% at idle. If it's higher than this it indicates a dirty throttle butterfly, blocked filter etc...

The oxygen sensor can be tested with a Lexia as well - by watching the voltage swing from 0.1v to 0.8v about twice a second at idle. Or you can connect an oscilloscope to it by back probing the oxygen sensor connector.

If you're trying to get to the bottom of tricky to diagnose problems it might be worth your time getting hold of a Diagbox/Lexia system, as beyond what we've already suggested you could be poking around in the dark a bit without more information.

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Mandrake
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Re: Xantia V6 running rich.

Post by Mandrake »

Allmostfrench wrote:
12 Aug 2020, 07:00
A quick update:
Took it to my local French Car shop and they could not get it to throw any codes....
Not surprising. This old engine ECU is a bit of a simpleton unfortunately! Unless the engine is just about on fire and about to explode it rarely sets fault codes. :lol:

It will detect basic, obvious problems like oxygen sensor unplugged, map sensor unplugged, etc but it cannot diagnose or set fault codes for more subtle problems. For example it cannot detect slow (contaminated) oxygen sensor response, it has no misfire counter so the car could be misfiring like a dog and it will not set any fault codes at all, (been there done that!) and subtle problems like a worn TPS will not be detected.

It also does not detect or report problems with the fuel trim so won't set a fault code if its running rich or lean. In fact it cant even report fuel trim in live data let alone fault codes!

It's a really simple ECU so you need to look at what live data it has available yourself to observe idiosyncratic behaviour rather than relying on fault codes.
They pointed out that the coil packs had some cracks in the epoxy that they are potted in, although the car doesn't miss under load.
Cracking of the coil packs is quite common. It's not necessarily indicative of a fault, however if the cracks go deep it can cause misfires in damp weather.

I'm beginning to suspect mine is going again - I've replaced the coil pack once already a few years ago and the replacement is quite cracked through the epoxy again. It runs really well in cold dry conditions but feels a bit sluggish in hot humid weather...

The spark plug leads to the rear bank can also be problematic - on my first Xantia V6 two of the three rear spark plug leads were broken internally (open circuit) making the spark much weaker and leading to a misfire under load. The leads are also very short so have to be pulled quite tight to install them, if you're not careful you can pierce the insulation of the leads on the sharp hold ins on the plastic guides too. :?

I'm not sure if you're aware but another common problem on these engines is oil from a leaky tappit cover on the rear bank leaking into the spark plug wells. When I replaced the rear spark plug cassette/leads on my first V6 I found they were submerged in oil...

Allmostfrench
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Re: Xantia V6 running rich.

Post by Allmostfrench »

Thanks Simon!
There's plenty to go on with there!
I'm sure others will benefit from this information too.

Cheers, Chris.

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xantia_v6
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Re: Xantia V6 running rich.

Post by xantia_v6 »

re-reading the first post in this topic, I am inclined to think that the vacuum hose from the manifold to the main fuel pressure regulator (at the timing belt end of the engine) has not been reconnected.

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Mandrake
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Re: Xantia V6 running rich.

Post by Mandrake »

Or has split perhaps.

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ksanturion10
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Re: Xantia V6 running rich.

Post by ksanturion10 »

...yeah, and a marmot is folding chocolate bar :roll: