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

[addo]

It will probably show, then, logged clutch slip events in the gearbox ECU - whether permanent or temporary faults. I presume the 4HP20 has input and output speed sensors.

[Stempy]

Hardly a stock car you had there Stempy

Yes, the mods I did throughout the whole car were many and varied but all very subtle.

I'm intrigued by you upping the fuel pressure to 3.5 bars... what encouraged you to do that and what was the result ? I'm assuming that's vacuum hose off pressure you're quoting. Mine is a bit on the low side - 2.7 bars with the vacuum hose off when it should be 3, but I didn't think it was low enough to cause serious problems.

In an ideal world I'd replace the regulator but I have to carefully prioritise what work I do so as to avoid this car becoming (even more of) a money pit... (If it was a more lowly Xantia I would have got rid of it after this amount of trouble but a V6 is something special that's worth persevering with a bit more IMO, especially when I had always wanted one)

I upped the pressure as I had increased the airflow with the intake mods. May have given it a tad more pep or it might have been wishful thinking I still have the old 3Bar regulator which you can have if want it. If so, PM me your address.

Do you notice any difference with the fully synth oil ? Because of the problems this one has had with very noisy tappets I'm strongly considering treating it to fully synth when I do the oil change, although some have pooh poohed the idea of "fancy" oil.

Always used fully synth so have no point of reference for anything else. I think the main advantage with synthetic is that its performance remains more consistent throughout its life.

Interested if you can remember any more details on your gearbox problems... I think the root cause of trouble on mine is a worn out TC lockup clutch which unfortunately means a rebuild, but I will drop the gearbox oil when I do the engine oil to inspect and replace it, again, to see how it compares to the 4 changes I did to clean up the oil 6 months ago. I still have sample jars from last time... From the way its behaving lately I suspect there are significant clutch related containments in the oil again, causing mayhem...

The only problem I had other than electrical was that it would hunt between gears when accelerating which was caused by low oil level when the oil return banjo sprung a leak, after I fixed that and topped it up it was fine. Occasionally it would grab second a bit fiercly but I learned to drive around that. Electrically it would go into safety mode radomly, especially on damp days, but no fault codes were reported, after I had the big electrical clean up it was fine.

[Mandrake]

It will probably show, then, logged clutch slip events in the gearbox ECU - whether permanent or temporary faults. I presume the 4HP20 has input and output speed sensors.

Yes it has an input speed sensor after the torque converter but before the main planetary gears, it also has a road speed sensor in the diff. From those it can measure any excessive slip occurring on any of the clutch packs in the planetary gear sets based on the current expected gear ratio, and it does have clutch slippage fault codes in the list of potential fault codes.

Here's the thing though, it has NEVER logged any clutch slip related faults in all the time I've had it. Nada. I'm not surprised though, as I don't believe any of the clutch packs in the gearbox proper are slipping under load, I think they're all working ok even though they're probably reasonably worn by now.

The TC clutch on the other hand, although it does seem to be able to lock up fully when I've tested it, (3rd gear in snow mode, foot to the floor at 40mph which stays in 3rd and won't unlock the TC) it "feels" like its only just managing to lock up under full pressure, in other words its running out of spare pressure range to regulate the controlled slip due to more than normal pressure being needed. The auto adaptive learning can compensate, but only so far. If I could get a good look at the EDS3 current figure during driving I would have a better idea of whether its near one end of the range or not.

I still don't know whether the poor control of the TC clutch is due to worn out friction surfaces, contaminated oil directly affecting the grip of the friction surfaces, or whether its contaminated oil affecting the functioning of the valve block, or low regulated rail pressure. No easy way to know.

The only faults of merit that the gearbox has ever logged has been the occasional "intermittent engine speed signal" which it has logged maybe 3 or 4 times over more than 12 months. This is perhaps more important than I gave it credence at the time, as comparing the engine speed signal with the gearbox's own input speed sensor is how it measures the slip across the torque converter.

A flaky engine speed signal would confuse the heck out of the gearbox as it would think the torque converter slip was going all over the place and try to compensate by modulating the lockup clutch... Since the engine speed signal comes from the crank shaft sensor, if it was in fact a slightly flaky (or poorly gapped) crank sensor that would also upset the firing of both spark and injectors...

Could be well worth my time getting my new little digital scope onto the crankshaft sensor signal on the engine ECU plug! On the other hand I'm assuming the rev counter also gets its signal from the crank sensor and I never see any oddities with the reading, although a few pulses missing or out of time here or there wouldn't show up on the rev counter but would affect engine running.

[addo]

The trans ECU also receives signal from the CAS, so if the TC output (your input speed sensor vs CAS) is not within parameters it will show a converter fault.

Disclaimer: Only last weekend I witnessed an AL4 trans with good electrical (diagnostic) health demonstrate massive vibration and 1-2/3-2 hangup. The vibration was input bushing wear almost certainly, while the hangup was probably leak-past occurring after the line pressure sensor's point in the fluid circuit. So, weird stuff can happen.

[Mandrake]

I upped the pressure as I had increased the airflow with the intake mods. May have given it a tad more pep or it might have been wishful thinking I still have the old 3Bar regulator which you can have if want it. If so, PM me your address.

That's a very kind offer! I'll PM you my details later Due to house moving etc it would be a month or two before I'd actually get the chance to try fitting it (since its another manifold out job) but I would definitely try it. It's still possible that whilst my pressure regulator was working ok (albeit at 2.7 bars) on the occasions I've put the gauge on, it might be going awry at other times after prolonged driving as the engine heats up, the problems have been very intermittent and inexplicable after all, and I'm not sure if I managed to get the gauge on to it at a time when it was playing up really bad.

The only problem I had other than electrical was that it would hunt between gears when accelerating which was caused by low oil level when the oil return banjo sprung a leak, after I fixed that and topped it up it was fine. Occasionally it would grab second a bit fiercly but I learned to drive around that. Electrically it would go into safety mode radomly, especially on damp days, but no fault codes were reported, after I had the big electrical clean up it was fine.

Hmm, I've sporadically seen "hunting" for gear since I've had the car, and it has done it a little bit lately. Where you'll be climbing a hill, it will change up a gear then almost straight away change down again, then maybe up again 5 seconds later, all with no change in speed or throttle, like it can't decide what gear it should be in. Is that what you mean ?

Mine occasionally grabs in 2nd if I've slowed down for a round about and I then stamp on the pedal as its trying to change down. Mine has never gone into limp home mode.

[Mandrake]

The trans ECU also receives signal from the CAS, so if the TC output (your input speed sensor vs CAS) is not within parameters it will show a converter fault.

It's never shown such a fault. I'd have to check the fault lists in the Lexia next time it's connected, I'm not sure there is a specific fault code for excessive torque converter slip. If the ECU is as brain dead as the engine ECU then it probably wouldn't log a fault unless the clutch failed completely anyway!

I've seen an AL4 log clutch slip fault codes - but AFAIK that was only after it reached the "no drive" point...(low rail pressure caused that one)

[addo]

Since you mentioned economy a bit ago, I checked. My current consumption is about 25 and up MPG for heavy-footed suburban lugging, one up, aircon fan at 3/4 speed and blowing cold always; 200-odd kg of gear in the back. Never struggles, never gets hot ('stat works perfectly), and I have hit the rev limiter towing an empty trailer uphill in first.

[Mandrake]

Since you mentioned economy a bit ago, I checked. My current consumption is about 25 and up MPG for heavy-footed suburban lugging, one up, aircon fan at 3/4 speed and blowing cold always; 200-odd kg of gear in the back. Never struggles, never gets hot ('stat works perfectly), and I have hit the rev limiter towing an empty trailer uphill in first.

What engine and gearbox though ? I thought you had a 2 litre 16v with AL4 ? If so I can't see how comparing MPG to a V6 with 4HP20 helps... the 2 litre will win that game. I used to get a minimum of 24MPG on my 2 litre 8 valve with 4HP14 (good old mechanical/hydraulic box with no fancy electronic brain and TC lock up strategies) with lots of around town driving generally with a lead foot.

BTW isn't it the middle of the night there ?

[addo]

I get proper insomnia. Why faff about lying sleepless in bed?

The AL4 is supposed to be weak, unreliable, thirsty etc. In this case it isn't at all. As the car is somewhat loaded, I do feel it's a closer comparison vehicle for the V6.

[Mandrake]

I don't doubt that the AL4 is capable of better fuel consumption than the 4HP14 on the Series one 2 litres like my old Xantia... The AL4 has the same sort of intelligent ECU controlled TC lockup that can actually lock in all gears, even 1st in special circumstances like towing, unlike the 4HP20 which can only lock up in 2nd 3rd and 4th, and the 4HP14 which to my knowledge always locks up in 4th and is always unlocked in all lower gears...

Aggressive lock up of the torque converter in most/all gears when possible negates most of the drawbacks of an automatic IMHO, I'm just not in favour of the controlled slip system of the 4HP20 as it seems to be asking for trouble deliberately maintaining slip of a clutch under load even if its just 50rpm. I prefer the AL4's concept of fully locked with no slip or fully open. (Would 4HP20 torque converter clutches be dropping like flies at 100k miles without a controlled slip mode ? I bet not. Pity because in theory ECU reprogramming could eliminate the controlled slip mode making it work like an AL4)

I think the real reason the V6 is thirsty in around town driving is that it takes an age to warm up the engine, its well over 10 minutes of stop start 30mph driving to get anywhere near operating coolant temperature so you're driving on a cold engine. Combine that with an extra 200Kg of girth and (probably) higher friction losses at higher rpm due to 4 overhead camshaft and 2 extra cylinders and MPG plummets.

On the other hand it does very well on motorway MPG compared to a 4 cylinder - I'd say because (a) its warmed up properly on long trips, and (b) it has the low down torque to keep up with motorway traffic at very low rpm with long gear ratios (and TC locked up) thus minimising friction losses compared to a higher revving 4 cylinder.

[Mandrake]

Another quick gearbox update.

Since doing a ton of long distance but slow stop/start driving recently (house hunting/moving etc) the gearbox is definitely getting a bit cranky, gear changes are sometimes a bit rough and abrupt, (although sometimes fine) and the TC clutch seems to be shuddering quite a bit on power particularly at low RPM with wider throttle. Basically early signs of all the same symptoms I was getting last year before I did the four oil changes.

While emptying the attic I found my original 2 litre bottles full of the drained oil which I had not yet disposed of and it reminded me that although the oil in the small diameter glass test tubes after my last change looked pretty decent, the oil as seen in a 2 litre bottle was still more or less black, what's more when I tipped the oil out into the collection drum at the dump there was a lot of black carbon like sediment in the bottom of the bottle, so clearly the oil is still quite contaminated.

This made up my mind to do one last gearbox oil change while I can, I still have the use of my level ground for another week until we're fully moved out - after that we're going to be staying somewhere for a few months with no drive way and no level ground anywhere nearby! I've got the oil so hopefully I can get it done this weekend.

The real point of my post though is I've been wondering (a few months down the line) how practical a DIY hot flush would be ? In most regards it seems pretty straight forward - disconnect the two gearbox oil hoses going to the heat exchanger, connect clear hoses to each, one going to an empty drainage tank and the other to a 20 litre drum of new oil. Let the engine idle, the oil pump pumps the old oil out and new oil goes in.

The major snag I can see is how do you keep the amount of oil flowing in equal to the oil being pumped out, when the two are no longer connected in a loop ? Otherwise it may let the sump empty (and damage the pump) or overfill the sump and cause other problems. The two flows need to be close enough so that by the time 20 litres has gone through the level is within a safe range that can then be checked and topped up/drained as needed. I'm assuming that the return hose from the heat exchanger just dumps the oil back into the sump rather than going directly to the pump, therefore the pump won't control the inlet flow rate thus gravity feed might overfill the sump quickly.

Does anyone know how the professional hot flush machines match the flow rates ? I'm assuming that they use some sort of 4 port 2 impeller pump, configured a bit like a turbocharger - the oil that is being pumped out of the box by the oil pump turns an impeller which is connected by a shaft to another impeller on the return hose which acts to pump fresh oil back in at a controlled and almost equal rate. Good idea but not easy to build DIY.

One other idea I had was to put both the drum of new oil and the collection tank on a scale and have some sort of adjustable valve to control the flow from the tank into the gearbox - if the oil flow is equal the scale weight should stay the same, if it starts getting lighter you know oil is going in too fast and to slow down the flow a bit, or too heavy and the inlet flow rate is too slow!

Anyone have any thoughts, or am I getting a bit too ambitious contemplating a DIY hot flush ?

[CitroJim]

Anyone have any thoughts, or am I getting a bit too ambitious contemplating a DIY hot flush ?

Definitely too ambitious Simon and given the cost of the ATF you'd need and waste you'd be much better off spending the money on hoiking out the engine and 'box, getting a refurb'd TC and getting the 'box to me for a rebuild before it goes pop and potentially costs more to rebuild.


.

[Stempy]

Do what Jim says. If the old oil was that badly contaminated the filter is probably stacked full and we all know what you have to do to replace the filter (give it to Jim).

[CitroJim]

That's my line of thinking Stempy...

If the oil is black then basically something is not happy. All the HP20s I've had apart that had black oil in them looked like the Somme inside.

[Mandrake]

Thanks guys,

As much as it would give me great satisfaction to take the engine/gearbox out and do the job properly, it simply isn't on the cards now, in the near future, or even this year.

There is just no way it can be done in our current situation which means I either sell it before it dies, or coddle it and hope it hangs on another year. If it dies on me before then it can't be helped I'm afraid. Harsh but true.

I thought it was at deaths door last October with symptoms far worse than its exhibiting just now, but flushing clean oil through it got another 6 months of relatively normal trouble free operation from the gearbox. I'm not convinced that its dead yet if the oil could be thoroughly cleaned and at the end of the day its all I'm able to do in my present circumstances.