Xant 2.0i VSX auto - MOT fail with high emissions at idle

andmcit · Unread post by **andmcit** » 23 Nov 2010, 09:37

I hate things like this that I can't see or fix with a spanner and end up being
at the mercy of MrMOTman. My pops's M plated 2.0i auto has just failed it's
emissions with high readings at idle.

All the readings are fine and well within 2006 car pass levels when the car is
doing anything apart from idle but HC is miles over the pass threshold at idle.
The tester suggests it's over fuelling because of a duff sender foxing out the
ECU. I have to say, it's fairly thirsty ATM. Mileage is around 95k miles.

Damned thing has a leaky rear HC too but I'm going to have to work out
this emissions issue first. Is there a 'favourite' failure sensor, a checklist I
can try to rule things out or is this purely the job for a Lexia?

Any helpful suggestions?

(and no, he doesn't want to run a diesel instead!)

Andrew

addo · Unread post by **addo** » 23 Nov 2010, 09:43

You're going to have to look at warm idle parameters - injector dwell, timing, coolant temp reading, oxygen sensor voltage, idle motor steps.

handyman · Unread post by **handyman** » 23 Nov 2010, 12:20

Hi Andrew, try the idle valve sensor, it is usually the problem. It should be located on the throttle body. Without checking the parts listings, I seem to remember two different units being available for these early cars. Can be dismantled from the body and cleaned, but be careful as it is a delicate instrument. Also worth cleaning the aperture in the body.

Did the HC readings flag up the lambda sensor as that could also affect the readings?

Duff spark plugs or gaps to wide? Blocked or missing air filter?

Lastly, is the bottom pulley in good condition? I found a damaged one on a 1.8 16V engine had upset the running at idle. Caused an increase in fuel consumption at idle.

H

citronut · Unread post by **citronut** » 23 Nov 2010, 13:44

it always used to be said if the HC is to high i was an ignition fault, but im not so sure thats true of cars with all these sensors everywere,

i also find when the idle control stepper motor is playing up the rev's are all over the place,

and they dont like carb cleaner upm, its ok to clean them with carb cleaner but they seem to completly fail shortly after,

regards malcolm

andmcit · Unread post by **andmcit** » 23 Nov 2010, 14:21

The figures shown up:

Fast Idle Test
_______________Min limit________Max limit_________Actual value
CO % vol:________.n/a.___________0.300_____________0.128
HC ppm vol:______.n/a.____________200_______________28
Lambda_________0.970___________1.030_____________1.005

Natural Idle Test

RPM l/min:________750____________950_______________909
CO % vol:________.n/a.___________0.500_____________2.052

Thanks for the pointers. I'll have to have a prod about after work.
It's had new correctly set spark plugs and AFAIK the timing IS right
having had a new belt recently with the cam/crank pinned correctly.
It idles fine although it seems reluctant to fire when warmed up
- certainly not as instant as it is clay cold first thing in the cold.

I'm guessing I'm concentrating on item 11 in the diagram below?

Andrew

Unread post by **citroenxm** » 23 Nov 2010, 15:12

Does he "pussy Foot" about, or is he heavy footed, there is NOTHING like a damm good hammering (When HOT) to sort out emmisions!!

Otherwise...... "Get a Diesel" ..... LOL LOL ...

Paul

(Sorry, just could not help add that Andrew)

Unread post by **CitroJim** » 23 Nov 2010, 16:58

To my mind, your CO is a little high on the fast idle test. It should be practically nothing at all...

As said, plugs and so on but I'd be looking closely at the cat and the coolant temperature sensor. Your admission that i's not keen to start when hot may indicate the ECU thinks the engine is colder than it is, thus richening the mixture. Being thirsty is a give-away too...

High HC is indicative of a rich mixture. Air filter nice and clean?

You'll be able to smell when all is OK. Generally high HC and CO at idle makes for a smelly exhaust, moreso if the cat is on it's ninth life...

Getting it really, really hot can help.

A Lexia session will be your friend too..

andmcit · Unread post by **andmcit** » 23 Nov 2010, 17:05

citroenxm wrote:Otherwise...... "Get a Diesel" ..... LOL LOL ...

Paul

(Sorry, just could not help add that Andrew)

I saw this one coming with you Paul (or Xac!) so thought I'd head you off at the pass:

(and no, he doesn't want to run a diesel instead!)

I'll just take the p!ss the next time you're all going on about kaput diesel lift
and main feed pumps and the endless biobibblebobble...

Yes, he drives a bit sedately. He also drives W plated 2.1 TD Xm auto..

Andrew

andmcit · Unread post by **andmcit** » 23 Nov 2010, 17:18

Yes, The first pass fast idle test failed with CO 0.166 and HC 45
with 1.039 lamda.

Another thing in the mix was the fact the car wasn't at it's 'optimum' running
MOT emissions temperature either - the place I take the cars to works on a
conveyor belt arrangement with two testers leapfrogging cars and it's a
case of forming an orderly que; by being really early means being first
through the door allowing me to make work for 9:00am.

I probably switched it off for about 30 mins after driving it to the centre
but did idle it a few minutes.

Andrew

Unread post by **xantia_v6** » 23 Nov 2010, 18:26

Things to check or substitute:

Coolant temperature sensor, Air temperature sensor, Fuel pressure regulator, vacuum connection to fuel pressure regulator.

DickieG · Unread post by **DickieG** » 23 Nov 2010, 19:11

One important thing to check is the manifold pressure sensor, if the engine is the version I think it is the sensor is located on the bulkhead in front of the drivers seat, I once cured a Xantia 2.0 auto suffering from similar problems simply by removing the vacuum pipe from the MAP sensor and blowing through the pipe to dislodge crud at the manifold end of the pipe, simples

andmcit · Unread post by **andmcit** » 28 Nov 2010, 18:20

Still in the dark on this one.

A couple of usually handy garages couldn't offer to help as the diagnostic
on the car is too old for their kit!! Basically both suspected the lambda
sensor and then the cat if it's goosed.

I'll be hopefully be fitting a new Lambda sensor when it arrives tomorrow
and have a mind to buy an engine temperature sensor. Problem is there's
a nest of them on the back of the cylinder head and I don't know which is
which? I haven't had a chance to get alternate spares swapped off another
car I have as it's 50miles away and I've spent my available time sorting a
leaky rear height corrector; BTW why do they decide to just leak!?

Other points worth mentioning:
- the dash temperature gauge works although this may be fed from a different sender
- engine rad fans clearly get a sensor signal as they cut in and out correctly
- the MAP sensor feed pipe to the inlet is clear and clean and appears
clogg free at either end and onto where it's fitted

Do I need to make a run over to meet one of you Lexia'd guys to see if
anything flags up?

Andrew

Unread post by **CitroJim** » 28 Nov 2010, 18:26

The coolant temperature sensor will be the green one Andrew...

Hope the new lambda sensor cracks it.

Unusual for height correctors to leak. Where from exactly?

andmcit · Unread post by **andmcit** » 28 Nov 2010, 18:38

Cheers Jim. ECP do list a green temperature sensor for around 15quid so I'll
try that although a more thorough looksee will be given in that vicinity first
when the lambda sensor is fitted.

The leak is appearing around the rearwards facing hard plastic end cap.
Seems there is a leak around the seal in one half of the HC. Today I've
cleaned up and soaked the pipes joining the HC and have looked inside
the free end in situ but not arrived at any conclusive decision about why
it's leaking so it may need replacement. I REALLY don't fancy trying to
undo the high pressure feeds. Can see that ending badly unfortunately...

Andrew

andmcit · Unread post by **andmcit** » 04 Dec 2010, 10:08

I didn't want to count my MOT's before they were passed but on close
examination of the car last week I found a significant fault with the
temperature sensor!

More precicely, with the loom multiplug connector, which must have been
knocked I guess, as it wasn't properly connected onto the sender and it's
securing spring wasn't seated into it's collar. Probably after I had struggled
recently sluicing the whole crossmember and engine area with GUNK to
clean everything after a pinion leak which had the appearance of a major
hydraulic leak.

I had the car idling on ramps and was examining the lambda sensor when
I checked the green temperature sensor which didn't look square like it's
adjacent partners. I clicked it home to it's correct position and the car's idle
INSTANTLY dropped to almost half and ticked over far happier obviously
due to the car getting the right temperature signals to the ECU.

A pass this morning showed all is well. Yay!!

$\:D/$

The CO at idle failure at 2.052 is now showing 0.286!!
The lambda reading now 1.005 as opposed to 1.039 on one of
the original fast idle readings.

If I hadn't bothered trying to get this sorted like many who don't DIY or
give the local garage a go, the car would likely have been weighed in last
week. For the sake of a connection on a sensor - lesson learned here for
me that's for sure! Another upside is a more relaxed, nicer car to drive
which is much better on fuel! Who says MOT's are bad news!!

Andrew