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 »

Stempy wrote:Seemingly not as it looks like he's gonna have to have the dash out.....
Eh ? :)

At some point I'm going take the climate control panel back out to change one of the bulbs and maybe take the clock out to try to fix the wiring for that, but other than that I have no pressing need to take the dash board out...

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

Post by Mandrake »

Stempy wrote:Things must be going rather well as there have been no updates for quite some time. Could it be that the V6 is fixed?
Kinda. :)

It seems the elephant in the room all along was an ignition lead problem. Despite being extra careful fitting the last set of ignition leads there was something wrong with them in the vicinity of the top plastic cover - whether a break in the wire or a breakdown in insulation I don't know.

When I finally convinced myself to replace the ignition leads AGAIN (third time lucky!) most of the problems went away. Previously it would sometimes misfire so badly in wet weather that I was changing down to get up hills, now there is no loss in performance in wet humid weather and performance overall hovers between 80-100% of maximum all the time, so whilst its not perfect all the time, even when its "bad" its only a little bit down on what it should be, hence the reason why I haven't been spending time on it lately.

There are still a couple of unexplained issues though -

One is flicking the throttle just slightly above idle causes it to nearly stall, despite having just replaced the TPS. (No improvement at all) If I floor the accelerator from idle it also stumbles and splutters a bit momentarily (possibly even a minor intake backfire) - given that the ECU, coil pack, spark plug leads and spark plugs have all been swapped in the time that those symptoms have been present I can't see how it can be an ignition problem, but I'm not sure what to check next. It doesn't seem to have any effect on overall acceleration and performance though.

The other is that occasionally after a few weeks the performance at low rpm (below 2500) will drop somewhat and become slightly sluggish (no change in the performance above 3000 rpm) and disconnecting the battery for 5 minutes will immediately restore normal performance, for weeks at a time. As the ECU has been swapped I know it's not an ECU fault so my line of thinking is bad or misleading input data to the ECU is causing one of the adaption tables (knock retard, fuel trim etc) to get skewed erroneously, and the "reset to defaults" pulls it back into line again.

I know that there is something wrong with the heating of my replacement oxygen sensor - very occasionally the ECU will complain "intermittent: oxygen sensor open circuit", yet when I check it the oxygen sensor is working. As soon as I fitted this oxygen sensor I noticed that it was very slow to warm up - the old one would warm up in under 2 minutes even while idling, (reaching full 0.1 to 0.9 v swing) the new one takes far longer - maybe 4-5 minutes of idling and even then its not warmed up properly (only say 0.3v to 0.7v swing) until you drive the car.

Despite this the heater resistance is correct and its drawing the correct heater current of around 2 amps. What I'm thinking is that if the car is started and left to idle for a long time, (as on a cold morning) the ECU starts monitoring the oxygen sensor and using it for mixture feed back before the sensor is actually warmed up properly - as soon as it sees a couple of 0.455 volt crossings it starts using the oxygen sensor, but its nowhere near warmed up and nowhere near swinging across the full voltage range so will be giving inaccurate data with the ecu trying to adapt the mixture to this inaccurate data.

I'll replace the oxygen sensor again next spring with one sourced elsewhere and see if the slow oxygen sensor warm up problem goes away, and if so, whether this solves the ecu reset issue as well...

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

Post by Stempy »

Mandrake wrote:
Stempy wrote:Seemingly not as it looks like he's gonna have to have the dash out.....
Eh ? :)

At some point I'm going take the climate control panel back out to change one of the bulbs and maybe take the clock out to try to fix the wiring for that, but other than that I have no pressing need to take the dash board out...
Thought you had a kinky vent control....

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

Post by Mandrake »

Stempy wrote:
Mandrake wrote:
Stempy wrote:Seemingly not as it looks like he's gonna have to have the dash out.....
Eh ? :)

At some point I'm going take the climate control panel back out to change one of the bulbs and maybe take the clock out to try to fix the wiring for that, but other than that I have no pressing need to take the dash board out...
Thought you had a kinky vent control....
Fixed, and documented some weeks ago. Keep up! :-D

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

Post by Stempy »

#-o :oops:

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

Post by larppaxyz »

Works for me.

Not a new car after my TPS replacement, but good enough. There still is that spike around 3000 rpms, but it took almost 1.5 month to appear (as compared to few days before) and it's not that bad. I'm happy with my car now and i won't do anything to "fix" it anymore.

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

Post by Mandrake »

Interesting, for me the replacement TPS seemed to make no difference. I don't have the sudden power spike above 3000 rpm anymore (at least 95% of the time its not there, very rarely it might be there just after a cold start during heavy acceleration but it quickly goes away) however I don't know which change solved this problem. (I think the ignition leads, but I can't be sure)

I still have a bad stumble/flat spot flicking the accelerator just off idle which is sometimes noticeable when driving as a hesitation when accelerating from stationary and cannot seem to find the cause, all I know is this was not there when I bought the car.

It also sometimes still does a near stall/surge 2-3 times in a row after a hot start - it seems to be related to the hesitation above idle, I feel sure that the same problem is causing both symptoms, but I have no idea how to attack the problem or where to look.

Apart from trying to stall at idle and a slight hesitation off idle it doesn't seem to affect overall performance so like you for the time being (winter and no garage to work in) I've given up trying. I will revisit it in the summer though.

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

Post by stevieb »

I thought I'd chime in on this thread after I found it a few weeks ago (whilst looking for wiring diagrams).

Mine is the car on the 406 Coupé Club website with the "invisible caravan" issue that was mentioned some pages ago, and I thought I'd offer my latest updates in case they help, particularly with the common set of symptoms (and the randomness with which they come and go).

Firstly, I found the plug/socket at my fuel pump was corroded - there are pics of it in this thread - http://www.406coupeclub.org/PHPBB3/view ... 83&t=45544" onclick="window.open(this.href);return false; - cleaning these little blighters up made a HUGE difference, but never fully cured it. I still had odd days (usually damp days) when it was still a borderline slow-and-thirsty again.

Today, following the idea of electrical gremlins to their next step, I opened up the engine bay fuse box and pulled all the fuses one at a time to clean the terminals - the thread is here - http://www.406coupeclub.org/PHPBB3/view ... =5&t=45942" onclick="window.open(this.href);return false; - if I hadn't pulled these myself I would've said they were out of a Land Rover that had been green-laning.

These ideas may not help, but they're both free to try and might just work. Even if they're not a solution to this problem, somebody else may find the idea fixes their electrical issues...

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

Post by Mandrake »

Hi Steve,

Thanks for posting - I had a quick read of both threads, and yes I have read your invisible caravan thread before and I'm pretty sure I posted in it once too. :)

As for corroded connections - fortunately (or unfortunately depending on how you look at it !) I have no corrosion problems on the fuel pump or the fuse box - both are nice and clean and I've already cleaned the fuel pump connector thoroughly with contact cleaner and also had all the fuses out of the fuse boxes, clean the sockets with contact cleaner, and in fact replaced all the fuses with new ones as there were a some that were slightly oxidised... net change - Zilch! #-o

Did you ever replace your ignition leads ? Mine were definitely a large part of the problem - the original set on the car were intermittently open circuit when twisted near the point where they go under the corner of the manifold at the back - the first set I fitted I damaged and they were flashing over through a nick in the insulation to the rocker cover near the front plastic guide, the second set I was very careful fitting and yet somehow they had an intermittent fault which was largely responsible for the extra poor performance in the wet - I replaced them a 3rd time (3rd time lucky apparently) and the weather related fluctuations are now gone.

Previously wet/damp weather with lots of rain always meant bad misfiring and very sluggish performance - now although the performance does still randomly vary somewhat there is no correlation with the weather - I've seen poor performance in dry weather and extremely good performance in damp wet weather with heavy rain and flooded roads...and vica versa.

I see you were having trouble getting genuine bougicord leads - did you try mister-auto.co.uk ? About £45 including delivery direct from France...

There are a lot of interesting points surrounding this problem in your threads on 406coupeclub so I think I'll pick up the conversation there so I can reply to specific points. :) I have some possible explanations for a couple of the things you've been puzzling over.

BTW, is your 406 an auto or a manual ?

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

Post by stevieb »

Cheers Simon - I may well see you "over there" :-)

I did find the Mister-Auto website for the Bougicord leads but I haven't changed my ignition leads yet, mainly through shortage of funds, but also because I'm debating whether it's worth the investment anyway. My mileages are likely to increase an awful lot very soon, so it might not be financially viable to keep the car. If the Bougicord leads that are still available are unused original stock (therefore well over 13 or 14 years old) I'd be wary of using them anyway. Depending on the materials involved, the insulation might've begun degrading which might explain your repeated problems with them.

I'll update here if I come across any other improvements or tweaks in case it helps anybody else, otherwise I'll be hanging 'round on the Coupe Club site until I get shot of the car.

:-)

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

Post by Mandrake »

An interesting update guys - two things.

The first is that I tried the "ICV calibration reset" procedure from stevieb's thread on 406 coupe club. I've actually tried it before about 6 months ago and it didn't seem to do much then, but in hindsight I was suffering from an ignition misfire from faulty ignition leads at the time that was probably swamping any other more subtle problems.

Anyway I thought I'd give it another go - basically the procedure is on a cold engine, turn the key on (ignition on but not start) for 10 seconds, then off for 10 seconds, then repeat twice more, for a total of 60 seconds, ending with the key off again. Then start the engine normally.

I was a bit sceptical but I tried it on Friday morning before driving to the train station. WOW! Right from cold the performance was instantly back to 100% normal. None of that trying to accelerate from low rpm in 2nd gear with a wide throttle with the revs falling away as the torque converter locks up and it struggles to pick up speed, just good strong acceleration in all gears with the revs increasing or at least staying constant during the torque converter lock up transition.

The car has been driven on a number of short trips since then and a couple of longer ones and so far no noticeable loss in performance, its running really really well. :) I also noticed when I got home tonight to peer under the bonnet while it was still running that the idle sounds "different" to how it has recently - smoother and yet more throaty and V6 sounding in the engine note. A nice V6 burble to the sound that has been missing a bit lately.

I'm a bit sceptical that the ICV itself is somehow "calibrated", especially when the engine is not running as the ICV is a two pole 90 degree stepper motor with PWM control - there's nothing to "calibrate", except learning the required opening by rpm feedback when the engine is actually running.

Possibly the reset procedure does something similar to disconnecting the battery for 10 minutes, although it does seem to be more effective. In any case I doubt whether the improvement will be permanent without doing it from time to time as I'm sure there is an underlying problem gradually "corrupting" the ECU maps (fuel trim and/or knock retard) depending on driving conditions.

Which leads me to my second point - I've had an email conversation with the tech support at lambdapower.co.uk over the last few days who was very helpful indeed - seems to be very knowledgeable on the subject (as you would hope) and even replied to my emails twice on a Sunday! =D>

After discussing the symptoms of the oxygen sensor and engine behaviour in general he's confirmed that the oxygen sensor I fitted last year is indeed the WRONG type. #-o

The first problem is the heater resistance measures 6 ohms but he confirmed the OEM type should be 3.3 to 3.5 ohms. If we assume an average voltage to the heater of 13.8 volts that means the OEM heater should be about 57 watts while the heater in this one is only 31 watts, out by nearly a 2 to 1 ratio. That would go a long way towards explaining why the oxygen sensor just won't warm up properly at idle and is relying largely on hot exhaust gas to warm up.

This means that any time there is extended idling (traffic lights, de-icing the car etc) or light cruising the oxygen sensor is running too cold and giving inaccurate readings to the ECU, which could easily be causing "corruption" of the fuelling adaption maps over a period of time.

Once they get corrupted far enough the engine may start lean or rich misfiring, and lean misfiring may have a knock on effect (ha ha) of causing the engine to ping and the knock sensor to start pulling the timing back, thus corrupting the knock retard maps as well - which may be where the main loss of low rpm power comes from. (As the power loss only occurs at and below 3500 rpm and I believe the knock sensor is ignored above 4000 rpm or at least has a lot higher triggering threshold)

Another sign its the wrong sensor is the original has a brown connector with a keying bump on one side while the replacement has a black connector with the keying bump on the opposite side - the lambdapower guy knew straight away about the brown versus black connector and asked me if the replacement had a brown connector or not.

Finally the part number I dug up in my ebay receipt is not a Bosch number so we believe (although can't be sure) that it may not even be a Bosch sensor. #-o

So I've decided to order the proper OEM sensor from lambdapower (about £83 compared to £140+vat from Citroen) and fit it. I probably won't get a chance to fit it for 2 or 3 months though due to winter weather and lack of shelter to work in. ;)

But at least I definitely know now that the fitted sensor is not the right one and that my suspicion that it is not warming up properly has been confirmed. For the moment the engine seems to be running very nicely - if I have to do this magic key on/off reset every couple of weeks in the mean time until I can get the sensor replaced I can live with that...

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

Post by stevieb »

Sounds like you're making progress there Mandrake... :-)

I should point out the ICV reset/re-calibration/black-magic is a bit sensitive to the times - i.e. make sure the key is in each position precisely ten seconds - otherwise it has no effect. I've read one or two cases where it's taken people a few attempts to get it right.

EDIT - I see some of what I wrote was covered higher up this page.... :oops:

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

Post by stevieb »

Hehehe, this is now coming full-circle.

Whereas I'd previously only suffered a slight cough, probably from one cylinder, I now have a very definite mis-fire - that unmistakeable sound of fuel being ignited somewhere along the exhaust instead of inside the combustion chamber. It isn't constant, but makes itself heard every so often and I think is the cause of my increase in fuel consumption. It's only marginal at this stage, and power-loss is noticeable but not horrendous, so I need to decide whether to live with it or invest in new plug leads.

I don't intend keeping the car too much longer so new leads might be a false economy (especially as money is tight right now), but then again my mileages are creeping up with the current job and they might pay for themselves at the pumps before I get chance to change cars. And if I change the leads only to find limited success and learn that a new coil-pack will help too, will I feel compelled to finish the job off with one of those and the added expense involved...? Decisions decisions...

EDIT - I forgot to add that I did a full bunch of resets/calibrations on the throttle and ICV after popping out my fuses and clearing the ECU the other day - and the car progressively lost its edge again. I reset the ICV last night and it seemed to go well. First thing this morning the car was fine and pootled down the M1 without a problem (apart from the occasional "pop" from the mis-fire), but each successive stop-start of the ignition has returned it to the less energetic and thirstier state. Clearly the ECU is learning things and adjusting its working parameters at every start-up. If what it's learning are bad habits due to readings being out of spec (bad sparks giving the lambda false readings, or in your case Mandrake, an incorrect spec lambda) then it makes sense that the car will behave out of spec too...

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

Post by Mandrake »

If you're getting popping in the exhaust its a misfire, it's most likely ignition related as that would lead to a lot of un-burnt fuel and oxygen in the exhaust, mine was bad enough at one point that I was getting backfires in the air filter box when snapping the throttle wide open! :shock:

If you do change the plug leads make sure you change the top inlet manifold gasket (a couple of quid from Citroen/Peugeot) and I would take the opportunity to change the spark plugs too. Make sure you fit only the correct types - Bosch FR8KDC. I had a different type in at one point and had problems with plug fouling! Not with these ones. This engine seems to be fussy about the plugs you use.

An ignition misfire will also cause the oxygen sensor to read "false lean" due to all the unburnt oxygen in the exhaust, the ECU will try to compensate by making the mixture richer causing all the good cylinders to run rich and waste fuel, not to mention foul the plugs from rich running and potentially damage the cat as well.

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

Post by stevieb »

Mandrake wrote:If you do change the plug leads make sure you change the top inlet manifold gasket (a couple of quid from Citroen/Peugeot) and I would take the opportunity to change the spark plugs too. Make sure you fit only the correct types - Bosch FR8KDC. I had a different type in at one point and had problems with plug fouling! Not with these ones. This engine seems to be fussy about the plugs you use.
Ah, the last time I bought an inlet manifold gasket I bought two, seeing as they were so cheap... :wink:

As for the sparks, I fitted some Denso Iridium plugs a couple of years ago (but only about 25k miles), so they ought to be good for a little while longer. They were still in great nick when I checked them last summer (and cleaned the oil dribbles out of the plug wells), and as they made a huge improvement when I changed them I'm unwilling to switch to anything else. I've come across people who swear by Bosch plugs in the ES9J4, and those who swear by NGK (strangely nobody rooting for Champion though), so whilst they're not giving me problems I'll leave them well alone. They're not the worst job in the world to do, on the off-chance I end up keeping the car.

I agree on the mixture issue - I probably ought to change it as the lambda sensor is the only in-flow sensor I haven't changed within the last 12-18 months (the non in-flow one being the knock sensor), but I've got to admit I find the workings of one a little bit hocus-pocus compared to any of the others. Mine is the original factory one, so quite possibly past its best by now. I've tried to undo it from the exhaust in the past to clean it up, but it's seized solid. As I'm now dependent on the car for work I'll be leaving it well alone to avoid any breakages that'll leave the car off the road. For the record I've replaced two steering racks, exhaust, front subframe, clutch and a multitude of other items in the vicinity of the lambda sensor, so I've tried shifting it quite a few times, and from all angles - it just refuses to budge.