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

[CitroJim]

Simon, if you know where to look, a MAP sensor is quite cheap.

The part number for cars since RP 8078 is 1920 AN. Before that 1920 9H

here's a reasonable 'AN' on the 'bay...

This is a '9H' just a bit dearer from the 'bay

When should torque reduction by retard be Activa Simon and when have you seen it in operation? If you can tell me then perhaps I can do a road test and see if mine is similar...

[Mandrake]

Second attempt to reply, a browser crash lost my whole post....

The revs dipping below idle as you slow down and stop is definitely wrong. To check this is not the TC staying locked up knock the gearbox into N before coming to a halt and see if it does the same thing...

Torque converter lockup not releasing quick enough was my first thought too, that or changing from 2nd to 1st too slowly, which is normally done just before coming to a stop. For some reason I haven't got around to try coasting to a stop in neutral, I'll give that a try.

If this is not conclusive then check the calibration of your throttle pot and check its actually working. Easy to do. Firstly, turn the ignition on and leave it on for 30s without starting up and without touching the throttle. Then, with the Lexia and with engine stopped, ensure that the throttle position is shown as 'IDLE' when the throttle is at rest and goes through (I think - from memory) 'MID-POINT' and 'FULL' respectively.

I've checked the butterfly calibration before and it seems to be fine, IDLE, MID and FULL are all indicated correctly.

Temperature. Remember the coolant temperature sensor (which the Lexia 'sees' is in the top hose effectively so will record the hottest coolant. The gauge sender is effectively in the bottom hose so what the gauge sees will be lower. 97-99 does seem hot even for the top hose as that's a full 10 degrees above stat opening and at that temperature the fans should be cutting in to bring it down. Definitely worth swapping that sensor just to rule it out. Normal operating temperature should be around 85-88 degrees (stat temperature).

I'll need to check it more carefully but I think the fans are not cutting in until the top hose reading from the Lexia is reaching 99 degrees, which does seem too high. However at the same time the water in the expansion tank only has a bit of vapour coming from it but is otherwise calm and bubble free, so I find it hard to believe that even the top hose is hitting 99 degrees.

There is no sign of the engine actually overheating and a replacement sensor is about £16 so I think its a no brainer to replace it, and it doesn't look too difficult either. If I put the front of the car up on ramps to tilt the engine back and also drain the expansion tank I shouldn't loose too much coolant either.

On whether or not the ECU does anything clever when it detects overheating I don't know but the gearbox does. It invokes a special cool-down map. It has to be jolly hot to do so though.

The highest I've ever seen the gearbox reach with vigorous country road driving is 105 degrees, which is still below the cool-down map threshold so I don't think there are any problems with the gearbox overheating.

What is the MAP reading with the engine off but ignition on? It should be close to prevailing atmospheric. On idle it should be around 350 mb or thereabouts. But again, the MK2 MAP sensor is very cheap and worth a swap just to see.

The MAP sensors I've seen are about £63 so I'm not sure I'd call that cheap. With the engine off the reading is around 980mb, idling around 380mb, so the sensor is "working", at least when I have had the Lexia on the car, however the point is whether its accurate and consistent or not. If the reading is sometimes inaccurate and other times ok it could easily explain the intermittent poor running. Without knowing the operating principle and construction of the sensor its hard to say whether such an intermittent problem is possible or not, but my guess is that it is possible if the sensor is old and flakey.

I've no idea when torque reduction is active or if it can be seen in operation on the Lexia. I just can't recall and would have to take mine for a spin to check.

The torque reduction can be seen in the ignition section of parameter measurement. There is a base advance figure which is calculated based on rpm, load, throttle position and so on as per normal, then there is a torque reduction figure which is subtracted from that to give the actual actual advance figure that is used, all three are displayed.

Sometimes the torque reduction figure is 0 which means base advance = actual advance. Other times you might see something like base advance 30 degrees, torque reduction 20 degrees, actual advance 10 degrees, in which case you can see the advance is only 10 degrees but would have been 30 degrees if the ECU wasn't throttling back the torque.

We know for sure that the gearbox can command torque reduction for example during gear changes (the change in engine note during a gear change with heavy throttle is quite obvious) but what we don't know as its not documented is whether the gearbox might command torque reduction for any other reason than gear-changes, for example gearbox overheating or clutch slip, and whether the engine ECU itself might also apply torque reduction to counter overheating or other perceived running problems...

[Mandrake]

Drat!! Just spent time retyping my post only to find that the first one did go through despite the browser crash...

Simon, if you know where to look, a MAP sensor is quite cheap.

The part number for cars since RP 8078 is 1920 AN. Before that 1920 9H

here's a reasonable 'AN' on the 'bay...

This is a '9H' just a bit dearer from the 'bay

Ah thats more like it, £20 I can stomach My RPO is 07905 so I guess I need the 9H version. I wonder what's different about them...

When should torque reduction by retard be Activa Simon and when have you seen it in operation? If you can tell me then perhaps I can do a road test and see if mine is similar...

I see it in operation even when idling or blipping the throttle, as well as when driving, it seems to vary constantly. I was under the impression from the documentation that it should only be used during gear changes...

I'll see if I can talk my "co-pilot" into watching the laptop during a test drive on the weekend to get a better idea of when the torque reduction is in effect and whether theres any correlation with the poor performance.

[CitroJim]

Ahh, that's better Simon, the last paragraph makes more sense now The first post was there but a bit was missing!

I'll have to see what mine does/says on the torque reduction front and get back to you. Should have a chance over the weekend.

The difference in the MAP sensors is the plug. The early (9H) ones have a square sided plug similar in style to say the one on the throttle pot on the throttle body or the coolant temperature sensor and the later (AN) one has a curvy sided plug with small round pins. In fact the pictures in the links show the plugs correctly for each variant.

[xantia_v6]

re the rpm dropping after coming to a halt, R252DVC would do that occasionally, after a 2 hour non-stop run at 90 MPH it even stalled, so this might be a quirk of the auto-adaptive idle speed control (my current V6 does not have this behaviour).

If you could remove the oxygen sensor from the pipe, I imagine that a blocked exhaust would become evident through the release of pressure?

[addo]

I welded in a 1/8" NPT female bung for pressure gauge readings between fanimold and cat with a cheap boost gauge and capillary tube, however latent heat kept melting the tube connection (soft solder). Brazing would have worked better.

[Mandrake]

re the rpm dropping after coming to a halt, R252DVC would do that occasionally, after a 2 hour non-stop run at 90 MPH it even stalled, so this might be a quirk of the auto-adaptive idle speed control (my current V6 does not have this behaviour).

Back in March when it was cold I did have mine stall a few times soon after starting due to the revs falling too low and not quite recovering, then through the summer it stopped doing it completely for many months.

Can you elaborate a bit on the "auto-adaptive idle speed control", is this a feature of the engine ECU or the gearbox or a bit of both ?

If you could remove the oxygen sensor from the pipe, I imagine that a blocked exhaust would become evident through the release of pressure?

I would imagine so, however without another to compare it against, I wouldn't know how much pressure through the hole would be normal...

[Mandrake]

Just drove the 20 mile round trip to Glasgow and back, most of it 60/70mph on the M8, some in 30/40mph zones, and not the slighest hint of a groan or shudder from the gearbox despite trying to provoke it at slow speeds in high gears, and generally good behaviour from the gearbox overall in terms of shifting etc, it seems to have further improved since the day I did the oil changes. So the oil changes were definitely not placebo in effect, and there might be hope for this gearbox yet.

One symptom that I thought might be the gearbox is still there, but I'm now thinking maybe it isn't the gearbox. If I'm doing say 50mph and I put my foot down a little bit the revs will rise like there is a bit of slip in the torque converter lockup, then they will drop back again. EG a small surge in RPM that drops again. If I applied a moderate throttle the lockup clutch is opening letting the RPM rise about 600rpm or so for the same speed, sounding a bit like a down change, but its definitely still in 4th.

My original theory was that the lockup clutch was struggling to lock properly under load, with a little bit of slip to begin with and then letting go completely with heavier throttle, but tonight I tried engaging snow mode, in this mode the small initial rise and drop in rpm is still there as you apply some throttle, but I can then apply a lot more throttle without triggering a kickdown and without the lockup clutch slipping at all - it holds steady and the car accelerates normally. So this suggests to me that the lockup clutch IS able to lock properly and pass the required torque without slipping when commanded to do so by the ECU.

I now suspect the small surge in rpm could actually be the engine putting out a little surge of torque that drops away again when you press the throttle, in other words related to the lack of engine power issue.

Engine power was down quite a bit tonight, I have to admit I am leaning towards the blocked exhaust theory, it does feel a bit like the engine is choked and unable to breathe properly until the revs climb up a bit. Whether its the cat or whether it could be a disintegrated centre silencer or back box is unknown.

It could still be a sensor fault causing lack of fuelling or the timing to be retarded, (since it does seem intermittent not permanent) a new MAP sensor is cheap and easy to fit even in winter so I'm going to do that first, and probably the coolant sensor as well, if no improvement I'll have to get someone to look at the exhaust system in a couple of months....it does seem that for the time being the gearbox is largely behaving itself and I'm just looking at an engine performance problem. I seem to be making some progress bit by bit.

[Mandrake]

Finally got around to comparing samples of oil from each oil change in test tube size bottles - in large bottles I couldn't tell any difference but the difference in opacity of the oil is pretty obvious now. The tubes from left to right are the oil that was drained in each of the four oil changes, while the 5th tube on the right is brand new oil for reference:

It's hard to appreciate the difference in photos, but the oil from the first change is completely and utterly black and opaque, even in that small size tube - I can hold it up to a light and see nothing at all through it.

The second change you can see a little bit of light through it but not much. By the 3rd its starting to look like oil and the 4th change whilst not as clear as the new oil is a long way towards being clean. (Bearing in mind that the new mixture of oil now in the gearbox will be 50% cleaner again than what was last drained out...)

So much for sealed for life, 100k and the oil looks like this...

[Hell Razor5543]

Did you offer number 1 to the local council traffic section for use as tar? It looks like it might be a suitable alternative.

James

[CitroJim]

Simon, your row of specimens is very interesting indeed

Number 4 is about what it looks like after 15K in a rebuilt 'box.

I really need to swap the oil in my V6 (both engine and 'box) and when I do I'll keep a sample to compare against yours. I reckon mine's dome around 20K now since the last change.

It'll be interesting to compare.

Did you offer number 1 to the local council traffic section for use as tar? It looks like it might be a suitable alternative.

James

I reckon it might be a good cat repellent. Or perhaps on seconds thoughts, knowing how it smell it might attract them

[CitroJim]

Simon, thought you'd like to see my specimen...

This I reckon is about 20-25K old. It looked crystal clear as it was draining but as you can see it's not 100% clear in the eggcup - somewhere between your 3 and 4 I reckon...



I saved a load of time changing the oil. I measured the old stuff that came out (4.3 l) and measured the same back in... Using that method makes it a very easy job indeed

[Mandrake]

Simon, thought you'd like to see my specimen...

This I reckon is about 20-25K old. It looked crystal clear as it was draining but as you can see it's not 100% clear in the eggcup - somewhere between your 3 and 4 I reckon...

Yes mine looked fairly clear while draining too, at least the last two times, but it can be deceptive since the apparent clearness of the oil depends on both the diameter of oil the light is passing through, and the lighting conditions. (As well as the camera exposure in photos)

Trying to compare yours to mine in different size containers and different lighting conditions with different camera exposures won't really give any meaningful comparison, the best bet is to compare it to some brand new oil in the same size of container so there is a frame of reference in the same lighting conditions.

I saved a load of time changing the oil. I measured the old stuff that came out (4.3 l) and measured the same back in... Using that method makes it a very easy job indeed

How are you managing to get 4.3 litres out ? I'm getting almost exactly 4 litres out each time with the front of the car up on ramps...I pour about 3.5 litres in straight away without checking the dipstick, then add the rest in 200ml amounts checking the dipstick in between.

Because my ground is not perfectly level I take two measurements, one with the car one way around, one with it facing the opposite way, and take the average of the two dipstick readings. (One is at the top mark with the car one way around, the other at the bottom mark, both are in the acceptable range and average to half way between the marks so I should be ok)

Do you think 20,000 miles is a good conservative changing interval to keep the oil and gearbox in best condition ? Pity that Citroen went for "sealed for life", with a 20,000 interval my box would have had 5 changes by the time I got it, if previous owners had kept up the maintenance. I'm willing to bet that it would have made a large difference to the longevity and smooth running of the box... It's hard not to think of no recommended oil changes being nothing short of planned obsolescence...

[Mandrake]

Did you offer number 1 to the local council traffic section for use as tar? It looks like it might be a suitable alternative.

Nope, funnily enough the consistency is nothing like tar, its just as runny as new oil, in fact if anything its more runny and water like...

[CitroJim]

I think 20,000 miles is a good one Simon and what I try to practice...

Point taken on the oil sample. I'll get another eggcup and fill it with new oil...

I drained mine on high and on level ground, no axle stands or jacks used. Just popped the car up on high with a shallow catch container underneath (my trusty giant cat litter tray) and drained. Measured the old stuff using a litre plastic IKEA measuring jug I keep specially for the purpose...

I wonder about the calibration of it because 4.3 litres on that was not quite 2 of the 2 litre bottles of the genuine Citroen stuff so let's agree on 4 litres!!!