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

[Mandrake]

When is Mot?

18th August, but given the uncertainty of failing on multiple points (rust hole, emissions, front wishbone bushes, possibly a hydraulic leak at the front) I was hoping to take it in late July for maximum time to remedy any failures. All of the above are marginal and might or might not fail, for example the wishbone bushes have looked dodgy to me for the last two MOT's but may get picked up this time if I'm unlucky...

You're a light weight.... I was up at 7 (lie in for the weekend, when small children always seem to want to get up early!), took the boys and bikes to Helix park at Falkirk, saw the Kelpies, then we ended up on the other side of the canal, and rode all the way up to Falkirk Wheel and back. I was towing Toby in the trailer, which makes it hard going! About 15 miles in all - first time I have ridden my bike in about 10 months...now my backside is sore!!

Oi, you're putting me to shame. I'm just not fit at the moment and readily admit it. There was a time when I did weights workouts and / or went cycling a lot but not in the last year or two...

Re the sill - sure I can weld that, will PM you.

Thanks, hopefully it's not too serious. Welding is one thing though, how do you paint over it and make it look original so their attention is not drawn to any repairs ?

Given that the symptoms seemingly fit a valve timing problem - what about a worn cam (or cams), given the apparent patchy history of oil changes....??

Well, actually that was one of my two ideas that I've been mulling over today. What else can affect valve timing apart from camshaft timing ? Valve lash...

And we know that I've had problems with noisy hydraulic lifters on this engine, probably due to oil change neglect before I got the car. The current situation for nearly the last year is that all the lifters are silent when the engine is cold, but when it warms up there are a few - maybe three or four out of 24, somewhere near the middle of the engine that get very noisy and clattery. (I know its not the injectors because the noises didn't move or change when I had the other set of injectors in)

Reading I've done suggests that a lifter that has a "high leak-down rate" will be noisy when hot but can be quiet when cold - I'm assuming the reason is that the non return valve is slightly leaky and when the oil is cold and thicker the leakage is not enough to prevent it from working, but as the oil heats up and thins the lifter "collapses" and effectively gives you a large amount of valve lash for that particular valve - every time the cam pushes down on it the lifter fully compresses instead of maintaining its pumped up length.

How much travel a collapsed lifter has I don't know, but when you consider normal valve lift is only 12mm or less a few millimetres of lost valve travel would make the valve open later and close sooner, which would have an effect on how that cylinder performs compared to the others. Possibly it would affect the mixture and cylinder pressures in a similar way to cam timing errors, I'm not sure. It would only take one cylinder with abnormal cylinder pressures and/or running lean to cause knocking that retards the timing of all the cylinders.

One of the consistent symptoms of this problem is that the engine runs perfectly from a cold start and only starts to misbehave a few minutes later when it warms up - I had assumed that the rich mixture and cold cylinder walls when cold helped combat the lean mixture and tendency to knock, and thus explained why it ran ok when cold. (Maybe they do contribute)

But I had forgotten that the lifters are silent for about the first 5 minutes or so from a cold start and then get noisy. Could it be when a few of the lifters start getting noisy and collapsing under load thus reducing valve lift on a few individual valves that symptoms appear ?

I do remember back when I first treated the oil for noisy lifters that it did have an immediate effect on making the engine run better, although it didn't last more than a few weeks, but then, neither did silent lifters when hot last more than a few weeks after treatment.

Another possible factor is that I now have a thinner grade oil in the engine than I used to, and this could have been a mistake if the lifters are a bit worn and leaky, especially on a worn engine...

I previously used 10w-40, (and have no idea what was in it when I got it) but I now have 5w-30 in it. The 5w doesn't matter but the hot viscosity of 30 may be too low for worn lifters when the oil warms up, so I'm seriously considering going back to 10w-40 again, (or maybe 5w-40) so that the hot viscosity is a bit thicker. It could be the engine clearances are a bit worn due to lack of oil/filter changes in its past, so might have slightly lower than normal oil pressure with a thin oil that contribute to lifters misbehaving.

It's nearly a year since the last oil change so it's due anyway, so what do I have to lose going back to 10w-40 ? (It's one of the recommended grades in the owners manual)

Of course if its that sensitive to oil viscosity it means either there is low oil pressure from general wear, or some worn-out lifters - I have no idea what is entailed in changing or removing lifters in this engine, (or even how you would figure out which ones are faulty when the ones I think are noisy are beneath the inlet manifold) I'm guessing its a camshaft out job not for the feint of heart so if the thicker oil doesn't help and it is the problem it's going to be out of my means to fix it...

Another thought along the low oil pressure theory - if the filter changes were so neglected in the past could the oil pump sump pickup strainer be clogged ? Perhaps its worth actually measuring the oil pressure, hot and cold, and inspecting the strainer depending on the result ? It might not be low enough to bring the warning light on, but perhaps the oil pressure when hot is low enough to cause marginal lifters to misbehave...?

[lexi]

If you went to see that car with the issues it has got now, would you buy it?
Leave alone, run for summer, then bin it. Look for a better car. There is nothing to endear on that one.........just nothing.
Forget the time spent on it, that doesn't matter now, it's gone just like money on a horse.

[Northern_Mike]

If you went to see that car with the issues it has got now, would you buy it?
Leave alone, run for summer, then bin it. Look for a better car. There is nothing to endear on that one.........just nothing.
Forget the time spent on it, that doesn't matter now, it's gone just like money on a horse.

Yes I would agree with that. Remove good parts (brakes, leather, fuel system bits that have been changed etc) , buy another that at least goes, isn't rotten and changes gear properly.

There is only so much of one's life that one can spend on any car/hobby. The stage always comes when it's time to say "(-expletive removed-) it" and get rid.

I understand that you've spent a lot of time and effort on the car and probably want to know what the hell is causing the problem, but seriously, life's too short. Treat it as a great learning experience, which is has been, and say goodbye to it. I'm sure there's enough non - rotten V6s out there for not much more than double what you'd get even at scrap value, which considering you were (I know you're not, it's been done) going to shell out on a timing belt kit etc is not a huge extra amount.

[Mandrake]

Don't worry Mike, it's very close to being given up on, I had that epiphany on Saturday. It all depends on the MOT results, really. If it's an emissions failure and the cause is the unknown engine problem then that's probably going to be the end of it.

The problem with your suggestions is that I don't have any off street parking to park let alone strip a car - once the MOT runs out I believe it's not even legal for me to park it on the road ? In that case I'm really screwed, I would have no choice but to get rid of it (eg scrap yard) as I can't leave it parked on the side of the road, can't strip parts off it, and wouldn't have room to park a replacement car. I'm in a really bad position at the moment for working on and storage of cars.

Buying a house has stalled for the moment, not for lack of money but for lack of houses on the market in the last couple of months.. which means we're almost certainly still going to be at the same address when the MOT is due, which was NOT the original plan...

If there is anything reasonable I can do to patch it up for one more MOT, running well or not, then I need to try as it's going to be a huge inconvenience for us having to dispose of a car and buy another in our current situation and it would result in the car going to a scrappy unless another member would want it for parts. If we were moved and had off street parking I would buy another and strip this one for parts as you suggest, but I just can't at the moment.

Once we've moved house and I have better facilities and a bit more room I can then look at replacing it, and I almost certainly will between this MOT (assuming it can pass) and the next one.

By the way I wouldn't say the car is "rotten", I think Richard would agree that it is remarkably lacking in rust for its age, certainly compared to his two year newer Xantia which had major rust problems by the end. I think we were just unlucky to find one of the very few (or maybe only) spots of structural rust on the car with our jack... I doubt a little bit of rust will kill this car, but a gearbox failure or an engine that won't pass the MOT certainly would.

[Northern_Mike]

I *believe* as long as it's taxed and insured you can park it on the street. It's illegal to actually use it. The ideal would be to buy another V6 then swap all your good bits over a busy weekend then get the shell removed on Monday

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[Mandrake]

I *believe* as long as it's taxed and insured you can park it on the street. It's illegal to actually use it. The ideal would be to buy another V6 then swap all your good bits over a busy weekend then get the shell removed on Monday

Well that's a small mercy, if true...

I'm kinda annoyed that moving house has been held up so much, if we were already moved and had room for two cars I probably would have been looking around for a replacement right now and stripping it down as soon as I got one...

[Hell Razor5543]

Have a word with Scottish forum members re storage, get Captain Slows Activa, and do a conversion (well, you can but dream!).

[Mandrake]

To get back to technical talk again for a bit - one of my theories was the lifters collapsing when the oil is hot, causing problems either due to valve lift being decreased on a few valves, or maybe the noisy lifters are enough to trigger the knock sensor due to the clatter. Either way that wouldn't be good.

My other theory is more related to the stumble on acceleration which just stubbornly will not go away. Yesterday afternoon I was having a little fiddle with those symptoms. I'm not even sure if these symptoms are related to the overall power loss or a separate issue, but perhaps they are related.

I'm talking about two things here - one is a kind of hesitation/stumble if I floor the throttle at idle, (which could potentially be a lean mixture or secondary ignition problem) which is sometimes accompanied by an intake backfire.

The other is if I tap the throttle quickly but lightly just off idle the engine basically cuts out for about half a second and tries to stall then recovers. (This is unlikely to be a secondary ignition problem as the throttle is only being opened very slightly)

I've had the scope on the TPS signal while doing that and as far as I can see the TPS is NOT faulty (it's a new one anyway) as I can see the TPS reading increases just like you would expect from tapping the throttle. I've also had the scope on the injectors while doing this and can see that the injection time sometimes drastically REDUCES when tapping the throttle in this way - which of course causes the mixture to lean out dramatically (as evidenced by a sudden lean swing on the O2) and cause the engine to try to stall.

The question is, why does it do this ? Yesterday I tried disconnecting the TPS and MAP sensors one at a time. The ECU can compensate to a degree for the absence of either signal as there is a lot of redundancy between them. With the MAP sensor disconnected the same symptoms occur - tap the throttle quickly just off idle and it tries to stall.

However disconnect the TPS and leave the MAP connected and tap the throttle the same way and the revs do NOT dip at all. There is a momentary delay where they stay the same and then they increase smoothly without any stumble, hesitation or attempt to cut out. The delay is to be expected as the MAP sensor is low pass filtered and vacuum doesn't change instantaneously either.

So the TPS signal telling the ECU the throttle is opening is definitely the causing the issue even though the TPS itself is fine. But why ? Why does a throttle opening slightly greater than idle tell the ECU to reduce fuelling dramatically ?

The TPS calibration is self zeroing - eg the ECU figures out what the minimum voltage is at key on and uses that as the "closed" reference, so it can compensate to a certain amount if the rest position is not quite what it should be, but I wonder if that only calibrates the idle position and not the throttle opening just above that ?

I have fiddled with the idle screw in the past in a futile attempt to to cure this problem, so I'm not sure if its back in the exact right position or not. Is there anyone with a V6 and Lexia who could check for me what the TPS voltage is at closed throttle ? Please ? (ICV opening percentage on a fully warmed up engine would also be very helpful)

I'm wondering if there is in fact a vacuum leak which is causing the ICV to close too much to reach idle, and that is upsetting the transition from idle to light throttle. Perhaps I do need to do a smoke test on the inlet to see if there is a leak somewhere. Anyone know of any "smoke in a can" solutions ?

[Northern_Mike]

Mine does the same thing if I snap the throttle at idle. I have no idea why. I honestly don't think it's connected to your other problem as mine otherwise goes like stink though the fast idle emissions were borderline at the MOT. If Hellrazor James wants to bring his Lexia around one day I'll see if I can get the voltages.

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[Hell Razor5543]

Mike, I am happy to do so any time this week.

[RichardW]

You don't need to worry about what the sill looks like, Simon (well not from an MOT point of view anyway!). As long as it's solid, and the welding doesn't look completely like pigeon poo, the MOT will nod it through. To do it properly of course, you would cut a piece out, then butt weld in a plate, grind all the welds back, fill it, then paint it close to OE spec with stone chip and top coat over. But that's a couple of days work....cutting out the worst, sticking a patch over it and undersealing it, whilst not pretty, will be a couple of hours. Thinking about it, you need to give it a bit of a poke in behind the jacking point to see if the inner sill and floor is sound - if it isn't then it's potentially a (much) bigger job. Pity, mine was sound in that area, I could have cut a repair chunk out before it went....

[RichardW]

We didn't check for a broken woodruff key in one of the cams.... but then that would require rather more dismantling I suspect

[Mandrake]

The thought did cross my mind Richard, but as you say that's major dismantling to check, and it seems kinda unlikely too.

If the key broke there would be nothing to prevent it eventually turning until it turned far enough for the valves to kiss the pistons. And touch wood, that hasn't happened in over a year...

A collapsing lifter or three on the other hand seems a lot more plausible, especially given the racket they make when hot, and the history of oil/filter change neglect, but it's probably even more difficult to check the lifters than the woodruff keys.

I will be going back to 10w-40 oil soon though instead of 5w-30 - lets see if that does anything for the lifter noise. If some of the lifters are really noisy when the oil warms up the mechanical noise might be directly triggering the knock sensor as well as affecting valve lift and timing, so there are two possibilities to cause trouble. Kinda grasping at straws but its due an oil change now anyway...

I wonder if it would even be worth trying 10w-50 on a last chance "not much to loose now" basis ? Anyone ever used 10w-50 in a modern engine or is that going to be too thick when hot ?

[lexi]

I would try a plain old 15/40 to test your theory. Weather is warm so will be ok.
I have oodles if you want a gallon for free.

I doubt it will do much. I changed oil and filter in that car right away. Used Fuchs 10w40 semi synth.
The oil gushed out on change and no signs of sludging. It wasn't the worse I have seen but was dark.
My theory is whoever put date on filter may have done belt too. He then got rid, as you don't put a date on filter and not change for 5 yrs Maybe it was off the road?

[Mandrake]

I definitely need to get the 5w-30 out and go back to at least 10w-40. 15w-40 isn't what I want though - that will make it thicker when cold but not thicker when hot. The lifters are not noisy when cold, only when hot.

It's when hot that the oil needs to be thicker, 10w-50 will be the same as 10w-40 below zero for cold starts but thicker than 10w-40 at 100 degrees. The only problem with a wide range multi grade oil though if its not synthetic is that it will have a lot of viscosity index improver's in it - which means when they break down (through shear) the hot viscosity will drop a lot more than a 15w-50 or 10w-40 for example.

I'm sure many people have noticed that hydraulic lifters can get noisy when the oil gets old and go quiet again with a fresh change of oil but maybe don't realise why - its not so much that the oil is dirty (unless it's really dirty!) but the loss of hot viscosity when the viscosity index improver's break down, especially with a mineral or semi-synth oil that needs a lot of VI improver's to attain its grade. What starts off as a 10w-40 may only be 10w-30 or less a year or two later...Whereas fully synth can achieve some multi-grade specifications without any VI improving additives at all, so doesn't loose its hot viscosity nearly as quickly with age.

Thinner than normal oil when hot may drop the oil pressure enough (especially on a worn neglected engine) that the hydraulic lifters don't have quite enough oil pressure to fill in each cycle, so they get noisy. In my case there are 3 or 4 which seem to be more prone to being noisy (maybe they are slightly leakier than the rest, and probably need replacing, really) but they're still silent when the engine is cold.

Anyway, we'll see what happens. I think the thicker oil will quieten the lifters down but whether that has any effect on the performance issues I've been seeing I don't know.

BTW when I checked the MOT history for the car a while back it doesn't appear to have been SORN'ed any time within the 10 years or so that I could see the report, I looked at the MOT reports and mileage and nothing seemed particularly odd, although the yearly mileage was quite low - only 5000-7000 miles or so...and it has had a lot of owners. Counting dealers I think I'm about owner number nine!