Xantia V6 broken exhaust (update: and rough low rpm running)

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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

A bit confused by the listings I've found. My RPO is 7905 so I think this one is the correct one ?

http://www.ebay.co.uk/itm/GENUINE-PEUGE ... 4abe4eddad" onclick="window.open(this.href);return false;

It's not 100% clear to me whether that's the ECU coolant sensor or the gauge sensor...

This listing confuses me:

http://www.ebay.co.uk/itm/TEMPERATURE-S ... 3365e0f975" onclick="window.open(this.href);return false;

Is that the sensor for the gauge or ECU ? (The description claims both...) Or the wrong one entirely ?

addo
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Post by addo »

Brown is Bitron, Green is ECU water temp, Blue is dash water temp.

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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Thanks Addo, I didn't realise there were three, I thought there was just the Green one for the ECU and a second one for the dashboard gauge. Where is the blue one located or is it fairly obvious with the infamous air filter box removed ?

My MAP sensor arrived yesterday but alas we were out for only 10 minutes during the delivery so I now won't be able to pick it up until monday...

In other news I did a lot of driving yesterday running the other half around probably over 50 miles and still no sign of gearbox groaning at all, in fact the gearbox was behaving itself quite well. =D> So I'm reasonably satisfied that cleaning the gearbox oil has made a massive improvement in the gearbox possibly to the point where there are no immediate concerns about its reliability or longevity...judging by the colour of the oil presented earlier in the thread it could possibly do with one more change maybe in a month or two to see how it's doing. So for the time being I consider the gearbox to be "fixed", or at least back to working as well as you would expect of an HP20 that has just passed 100k...

Regarding the lack of engine performance I observed its behaviour carefully during all the driving yesterday and noticed some interesting things:

1) There is often quite a big time lag between sudden application of throttle and actual engine output power, as much as a half second to second delay. This doesn't just occur below 2000rpm (although it's worse the lower the RPM) it can occur as high as 3000rpm. So for example I could be in 1st gear in sport mode at about 2500rpm and I could then suddenly punch the throttle down 1/2 to 2/3rd throttle and instead of being instantaneously pressed back in my seat (which is what it was like when I first got the car) there is instantaneous induction noise (as you would expect from the butterfly being snapped open) but a good half second or more delay before there is any real power increase and maybe a second for the power to reach maximum power - there is this gradual ramp up in power instead of instantaneous response which makes the throttle feel very unresponsive.

At higher revs you can also notice a delay in the power, say you're in sport mode in 3rd gear doing about 3000rpm, if you put your foot down you'll hear that nice V6 "brrrarrpp" but there is a half second to second delay from the time you punch the throttle down until you hear that noise, where the response should be instantaneous.

2) Likewise the rise then fall in engine revs when gently applying the throttle when cruising at motorway speeds I was describing earlier - if the revs are at least 3000rpm you can hear that V6 "brrrarrp" that tells you the engine is putting out power, you only hear that for about half a second then it goes away again as the revs drop. So it seems that when applying a small throttle increase when cruising there is a brief increase in engine power that drops back again. (Meaning that the cause of that little increase then drop of RPM is actually the engine not the gearbox as I first feared)

3) One more thing I noticed for the first time last night, fast acceleration from a standstill in sport mode with about 2/3 throttle there is quite a delay to power buildup as described in point 1, but every time without fail when the revs reached around 3500 there was an instantaneous large jump in power, like someone had flicked a switch - enough to suddenly push you back hard in your seat, and enough that it was as lively as I remember it being when it was working well. I could tell from the sudden increase in the engine noise that power was indeed jumping suddenly, not gradually.

All this has me thinking I'm on the right track with the MAP sensor, I really do think I have a sticky intermittent MAP sensor which is slow to respond.

Point 1 above could easily be explained by a sluggish response from the MAP sensor - for a given RPM and temperature, fuelling is more or less proportional to the pressure reading from the MAP sensor...if the pressure reading doesn't rise quickly when the butterfly is opened, for a period of time the fuelling will be lean, and possibly the timing may be retarded as well.

Point 2 could be explained by the ECU responding to the instantaneous increase in the butterfly opening giving a short burst of richer fuelling to prevent flat spots (eg basically the same function as the accelerator pump on a carb) but then a moment later the incorrect reading from the MAP sensor causes the ECU to back off the fuelling again. Thus a small surge in power each time you increase the throttle slightly that then goes away.

Point 3 could be due to a sudden change in the characteristic of the MAP sensor above a certain pressure, eg it may be that it doesn't work properly below a certain pressure.

Anyone think I am on the right track here with my observations ? It's rather frustrating that its pouring with rain today with the new sensor sitting at a closed post depot, I'm itching to get out and replace it. :-D

addo
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Post by addo »

I'm honestly yet to see a duff MAP, however that said I have last week just seen my first positively failed CAS on a PSA car that wasn't due to malpractice.

You should see pretty snappy changes in reading, from engine off to warm idle will show a distinct variance, also holding 3K RPM in neutral should show another change vs idle. Have you any easily installed "test load" of about 300kg to check open throttle (and throttle percentage) under load? Maybe get David Hallworth to compare with his engine on the other S2?

The missing sensor probably conforms to André's first rule - If you can see it, you can't touch it and vice-versa.

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CitroJim
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by CitroJim »

How odd Simon...

Power delivery should be instantaneous at all revs although point 2 I've noticed and I put it down to the TC briefly unlocking and then locking again...

It's like you have massive turbo lag... Which makes me think of something...

Well, there's no doubt the MAP and Coolant temperature sensors (the green one) need to be replaced to rule them out...

On the turbo lag symptom I've always noticed when replacing the airbox you have to be very careful to make sure the air inlet at the bottom correctly engages with the inlet air pipe that goes to the grille. It can slip off and obscure the air inlet to the airbox and this could have two ramifications: either the inlet is obscured and prevents the engine breathing correctly or it allows an excess of very hot air from the gearbox to be ingested. Both could cut power dramatically and account for the 'turbo lag'... Very easy to check and rectify. Also, if that's OK, is the air inlet pipe from the front of the car clear and free of kinks?

Also, this still could be blocked exhaust - it would present the same symptoms.

The blue sensor is a devil to get to and Addo is right with André's first rule - If you can see it, you can't touch it and vice-versa in this case. It's screwed into the rear cylinder bank under the throttle body effectively and buried in plumbing and wiring. The brown Bitron sensor is nearby too and just as difficult. Luckily, the one that fails - the green one - is very easy to get to :)

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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

CitroJim wrote:How odd Simon...

Power delivery should be instantaneous at all revs
Exactly, that's what I thought. A normal fuel injected non-turbo petrol like this, especially a 3 litre should have a very sharp more or less instantaneous throttle response - it did when I first had it, particularly in sport mode. Many was the time in the first month I had it that I accidentally spun the wheels in take off until I had learnt just how much to feather the throttle. :-D It hasn't been like that for ages.

I've been complaining about an unresponsive throttle for a long time now, but as its progressively got worse its now got to the point now where its blatantly obvious - I will sometimes have it in sport mode at a particularly busy roundabout, I'll plant the throttle about half way.....and wait a good fraction of a second for it to get off its backside and really start moving. Best I can describe is it does feel like turbo lag on an old fashioned turbo...Definitely not right, and it doesn't always do it either, sometimes the "turbo lag" is not there or minimal. On the odd days (especially cold dry ones) the throttle is quite responsive.
although point 2 I've noticed and I put it down to the TC briefly unlocking and then locking again...
See, that's exactly what I originally thought too - a little bit of extra slip in the torque converter lockup clutch when extra power is first applied, followed by the ECU quickly reigning it back in by increasing the clutch lockup to compensate.

But what gives it away I think is the engine sound at higher revs, you can hear the increase in power in the engine from the engine note, which then drops back again with the revs. So I'm pretty sure its a momentary surge in power from the engine when the throttle is first increased which then drops away again when it should hold steady.

If it was the clutch locking up more, that would apply more load on the engine and should increase the engine note not decrease it.
It's like you have massive turbo lag... Which makes me think of something...

Well, there's no doubt the MAP and Coolant temperature sensors (the green one) need to be replaced to rule them out...

On the turbo lag symptom I've always noticed when replacing the airbox you have to be very careful to make sure the air inlet at the bottom correctly engages with the inlet air pipe that goes to the grille. It can slip off and obscure the air inlet to the airbox and this could have two ramifications: either the inlet is obscured and prevents the engine breathing correctly or it allows an excess of very hot air from the gearbox to be ingested. Both could cut power dramatically and account for the 'turbo lag'... Very easy to check and rectify. Also, if that's OK, is the air inlet pipe from the front of the car clear and free of kinks?
Ah, that's an interesting point about the inlet to the air box - in the past I haven't paid any special attention to getting it seated properly, and I've had the air box in and out dozens of times... more recently I have been more careful though, fitting the bottom half with the filter element out and then wiggling the pipe and box to get the best mating between the two. Whether its an air tight fit or not I don't know, and I haven't checked the pipe to make sure its clear and not twisted - I will check that.

So a major leak there would draw in hot air from the engine bay decreasing the volumetric efficiency ? Speaking of that, according to the Lexia the air inlet temperature when the engine and engine bay is fully warmed up is around 45 degrees, does that strike you as unusually high ? What do you see on yours ? This is in ambient conditions between 0-10 degrees...I just assumed that even though the ambient conditions are so cold the engine bay heats up the air box enough to warm the air by the time it gets to the throttle body, but it does seem quite high...and the efficiency with inlet air at 45 would be significantly lower than inlet air at 10-20 degrees.

I don't think its a sensor fault either. When dead cold both air temperature sensors read exactly ambient, and they also always agree with each other. I know one sensor is mounted in the rear right corner of the air box, but where is the other one ?
Also, this still could be blocked exhaust - it would present the same symptoms.
I'm still keeping it in mind, but I'm hoping its not that, for obvious reasons. :lol:
The blue sensor is a devil to get to and Addo is right with André's first rule - If you can see it, you can't touch it and vice-versa in this case. It's screwed into the rear cylinder bank under the throttle body effectively and buried in plumbing and wiring. The brown Bitron sensor is nearby too and just as difficult. Luckily, the one that fails - the green one - is very easy to get to :)
Argh. How about the connector for the blue sensor, can I get at that to unplug it, give it a squirt of contact cleaner and reconnect it ? That's probably all that it needs doing to fix the intermittent gauge reading...

Regarding what might be wrong with the MAP sensor if it is faulty, are they prone to getting clogged up with oil ? There is a bit of oil on the inside surfaces of the inlet manifold and butterfly housing, I really should have made an effort to clean that a bit, but both times I had the inlet manifold off I was racing against the clock in poor weather conditions to get the job completed. Is it possible the tip of the MAP sensor inside the manifold is clogged with oil that has been deposited on there from the crank case breather ? There is also quite a layer of oily muck on the inside of the black pipe which comes out from between the cylinder banks and connects to the flexible pipe just in front of the throttle butterfly, which I presume is one of the crank case breather hoses ?
Last edited by Mandrake on 23 Dec 2012, 18:24, edited 4 times in total.

Xantidote
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Xantidote »

Glad to hear that your efforts with the gearbox oil changes have borne fruit, and you are still mobile - hope your work on the engine also proves successful (soon!)

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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Mandrake wrote: http://www.ebay.co.uk/itm/TEMPERATURE-S ... 3365e0f975" onclick="window.open(this.href);return false;

Is that the sensor for the gauge or ECU ? (The description claims both...) Or the wrong one entirely ?
So can anyone confirm that this green temperature sensor is the correct part number for the ECU coolant temperature sensor ? If so, I'll go ahead and order it...

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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Xantidote wrote:Glad to hear that your efforts with the gearbox oil changes have borne fruit, and you are still mobile - hope your work on the engine also proves successful (soon!)
Thanks, I do feel like I've made real progress at last after almost having to give up on the car... :)

(In fact I had given up on the gearbox, and therefore the car, only doing the second oil change because I had already received the oil, and then did the 3rd and 4th change because it responded well to the 2nd change...)

Intermittent lack of engine power is certainly annoying but should be fixable, and isn't nearly the same scale of problem or imminent threat as a dead or dying gearbox...at least I'm still mobile.

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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by RichardW »

Simon

Here's what service.citroen says about the temperature sensors:

1338 77 NFP
TEMPERATURE SENDING UNIT
14X125
BE- - BLUE

1338 66
WATER TEMPERATURE SENSOR
14X125
MR- - MAROON
- UNTIL RPO 07728


1338 84
14X125
MR- - MAROON
- SINCE RPO 07729

1338 91
WATER TEMPERATURE SENSOR
12X150

It shows as Jim says, the blue one in the rear bank under the front to rear connector pipe, the brown one screwed into the side of the connector pipe and the last one (no colour listed) screwed into the top of the connector pipe. So that link you posted is for the correct green one =D> A shade under £30 from Citroen.

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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Thanks Richard,

Thats that ordered now. :)

In other news I fitted the new MAP sensor this afternoon in between the rain showers, and it didn't work. :evil: #-o The engine just would not start at all. With a sinking feeling I went to get the Lexia and sure enough, the new sensor is DOA. Not only did it immediately have a "pressure sensor coherence" fault logged, the live reading from the sensor was duff - reporting 130mb with the engine turned off...in fact when I plugged the sensor in while watching the Lexia the reading gradually crept down from ~900mb to about 130mb over a period of a minute or so, all with the engine not running.

To say this is a let down is an understatement. :roll: Now obviously I need to get it replaced or refunded but in comparing the two sensors I'm concerned about the quality of the £20 replacement as well, not just the fact it is DOA. The original is Bosch branded and has a taper inside the tube that reduces to a pinhole size hole through into the main sensor body, however the replacement (with no brand printed on the actual sensor) has a big wide hole into the main body of the sensor with the sensor chip and wiring all plainly exposed. I've attached a picture:
image.jpg
image.jpg (97.41 KiB) Viewed 138 times
What are peoples thoughts on this difference ? I'm inclined to ask for a refund and go elsewhere rather than ask for a replacement, but I'm not sure at the moment. My worry is that all the £20 MAP sensors will be the same knockoff design, with genuine ones up around the £65 mark.

Nothing is ever easy is with this car is it! #-o

addo
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Post by addo »

Your sensor rail voltage remains correct at around 5V?

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oneday
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by oneday »

i think looking at the quality of that one i would bite the bullit and pay the money. has anyone got a known good one you could try before you spend out on one.

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Mandrake
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Re:

Post by Mandrake »

addo wrote:Your sensor rail voltage remains correct at around 5V?
If you mean the 5 volt supply to the sensor, I didn't have time to check it (had to get the car working again to go out shortly) but I see no reason to believe that there would be a problem with the 5v supply from the ECU. The original sensor is back on again and working fine and gives believable mb readings on the Lexia. Pretty sure its just a DOA sensor addo.

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Post by addo »

Got to say, I have had nil power delivery issues since addressing the exhaust restriction on my 16V motor. It's highlighting some line pressure irregularities in the gearbox, but I'm hoping a solenoid change will see them fixed. Fuel usage has gone up because I'm not using compression braking (due to the trans symptoms) and probably zooming about a bit more with the excitement of it.