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

[Mandrake]

Let's face it. You haven't added anything constructive to the thread for about 80 pages, though you do like patronising and pooh-poohing everyone else.

I would unsubscribe, but the forum software doesn't really allow it. Nor does it block effectively....

Thanks Mike, I've saved you the trouble. You're now on my block list. Have a nice day.

Oh dear ... calm down chaps.

Don't worry, I don't get annoyed easily, but this is not the first time I've had hassles with (the other) Mike, not even the second time. My patience has finally worn out, that's all. I'm trying to solve a serious problem here, not get caught in endless non-constructive arguments with someone who doesn't have to be here in this thread in the first place. Trying to say the forum doesn't allow him to un-subscribe from and ignore my thread is BS, so now he is blocked.

[Mandrake]

kv of the fluids is probably your key to those different results - you're not squeezing them hard enough to add significant heat. It's well possible the cleaner has a surfactant added, this would help its action and also the characteristic you noticed.

Agreed. There was a small change with fuel temperature too - after many sessions and many applications of the fuel pump (which would warm the fuel slightly) the pressure drop would gradually increase, but only by maybe 1psi, and all injectors by the same amount, whereas changing the mix was an instant large change of 6 psi and stayed pretty much consistent afterwards too.

So in this sense injector cleaner is a con - its not cleaning anything in most cases (although I'm not saying that it couldn't) it's just increasing the flow rate by affecting the kv of the fluid. In closed loop mode the O2 sensor makes a correction to compensate but you end up running richer in open loop mode than before. If you're already too lean in open loop (as mine seems to be) it runs better - if you're already at the correct mixture it just makes it run even richer and waste fuel.

I think the next easiest thing for me to try is to connect a pot to the MAP sensor so I can "tune" the sensitivity of the MAP reading to bias it towards increased fuelling. (Higher pressure/voltage) If there is really a flow delivery issue with the pump/injectors at WOT it should still run lean, but if tweaking the pot allows it to run sufficiently rich at WOT that it performs normally that would tend to suggest a sensor input issue of some sort.

Obviously I'd like to see fuel pressure while on the move but unless I can borrow some equipment from someone I can't see how I can test that just now. As the problem happens at low RPM I could potentially put it in 3rd gear with the brake on and open the throttle so the engine is loaded down by the torque converter (for short periods of time) and see whether I can load it enough to get my oxygen sensor reading to swing constant lean. If I can then I can refer to the fuel pressure reading occuring at that moment - if its normal then I could rule out sagging fuel pressure. (Which then leaves injectors or injector control, ECU inputs, air intake issues etc)

[addo]

To pull a bodgy test of fuel pressure on the go, tee between the pressure regulator and rail. Carry your "leg" up to the scuttle and use a £10 fuel pressure gauge tucked down beside the N/S wiper. Make sure to use EFI rated hose and clamps and carry an extinguisher. You should spend less than £30 to do this.

I would be very surprised if your testing shows any lack of ability to fuel on demand. It's one part of the system that is very overbuilt.

[Mandrake]

To pull a bodgy test of fuel pressure on the go, tee between the pressure regulator and rail. Carry your "leg" up to the scuttle and use a £10 fuel pressure gauge tucked down beside the N/S wiper. Make sure to use EFI rated hose and clamps and carry an extinguisher. You should spend less than £30 to do this.

It's physically not possible to tee in between the pressure regulator and the rail. The pressure regulator is a press fit into the end of the rail, there is no hose between them.

Probably the easiest way to get a fuel pressure reading inside the car would be to get an extension with the PSA style snap lock fuel fittings on each end and a shrader valve in the middle and connect it directly to the output of the fuel pump - this is accessible inside the car with the rear seat tilted up and the plastic cover removed. I haven't seen those snap lock connectors for sale anywhere though and don't know what they're called to try to look them up.

I would be very surprised if your testing shows any lack of ability to fuel on demand. It's one part of the system that is very overbuilt.

I know, but I've ruled every possible cause out at least once, which means I've overlooked something and need to loop back around again with a focus on things that could cause lean running. The low voltage at the pump is a wee bit worrisome, do you think 12.6 to 13.1 volts at the pump terminals is unacceptably low when the battery voltage would have been over 14 volts at the time ? I should have a look at the wiring diagram and trace the path of the fuel pump supply.

[lexi]

Lexi, you know I'm a repressed slater. Who besides you and I, knows what a duchess is, or a zax?

I can tell you are a man who will have a go at lots. Good way to be. Random slating with diminishing courses ( Scotch and Burlington) are a thing of beauty and longevity. I can see you with the slating stick and boring machine Adam. I loved it all, though there are easier ways to make money but who wants easy.? I can drive and see my work everywhere. Even looking from my window, there is not a roof I have not been on and re-done or repaired. We did traditional Roughcasting (wet) in our trade too. Slater and plastering /roughcasting was a traditional trade here in Scotland.
Back on topic.

[myglaren]

it has inadvertently become a long and detailed record of the trials and tribulations of this car and would be better placed in the blog section. Is there a moderator who would like to move it to the blogs section for me ? I'll try to cut down on the massive posts and maybe spread multiple ideas across multiple posts so its a bit more digestible.

Moved as requested Simon.

Although very lengthy and verbose this has been and continues to be a very interesting and entertaining journal with lots of thought provoking ideas, some with satisfactory results and some leading nowhere but all a wealth of information.
Keep up the good work.

[addo]

I have a few of the click on hose ends; will check sizing.

[Mandrake]

Stevieb:

Have you seen or tried the "auto adaption of the richness" procedure in this document ?

https://dl.dropboxusercontent.com/s/vr4 ... tnvNfwT_mQ" onclick="window.open(this.href);return false;

I can't try it myself at the moment as my oxygen sensor won't stay hot during 5 minutes of idling so would skew the results, but I will try it after the oxygen sensor has been changed.

[Mandrake]

I have a few of the click on hose ends; will check sizing.

Do you mean the pump ones or the rail ones ? The ones at the rail are square adaptors with a lock button on both sides, the one at the pump are round adaptors with a squeeze ring.

Although I haven't measured it to confirm, I think the actual spigot on the pump and the rails is the same diameter with the same identity ring though.

All I actually need is a male spigot with the lock ring that will fit the click lock connector I remove from the pump as standard fuel hose fits the spigot on the pump with a hose clamp - that's all I used on my test rig and it worked no problems.

So a male spigot to click into the hose, some fuel hose clamped on the back end of it to a T that goes to the gauge, then another length of hose to the fuel pump. I already have everything I need except for that one length of plastic spigot to fit the click lock connector on the hose properly.

[xantia_v6]

Are the spigot the same as those on the fuel filter?

[Mandrake]

Are the spigot the same as those on the fuel filter?

I think so, from memory, but I haven't measured them to compare them.

I think I know exactly where you're going with that thought. Genius.

The filter on there now is metal and fitted only a year ago. Buy another one for a fiver, swap it over and saw the spigot off the old one. The only thing is whether there would be enough stub left to attach a hose - or should I just keep the filter intact so i end up with two filters in series but a full length stub to clamp a hose to ?

(Bearing in mind I'm trying to measure pressure drop at WOT, so don't want to introduce extra flow restriction)

[Mandrake]

Hmm, just realised I really need to be measuring after the fuel filter rather than at the pump, otherwise a fuel filter restriction would cause a false OK result if I measure at the pump... I could still tap in just after the existing fuel filter with the same fittings though, and thread the T loop hose back up through the fuel pump hole in the floor to get the gauge inside the car safely.

[Mandrake]

Not wanting to fan the flames in the "fuel doesn't matter" debate, but I filled up with BP Ultimate (97) a few days ago instead of Shell V-Power (99) and the car is running quite a lot worse.

This time I have my scope connected to see if there are concrete changes in the way the engine runs rather than just my subjective impressions, and the answer is yes - the O2 sensor is clearly showing the car is running lean more often and more severely. I'm now sometimes seeing it run lean under WOT as high as 3000 rpm whereas before it was only doing it below 2500 rpm.

Once again there is a clear correlation between low power and a lean O2 reading under conditions (near WOT) where it should be running rich. I want to be clear and say that I don't believe this is related to the difference in octane between the two fuels - lower octane will not make an engine run more lean as far as I know, in fact an ECU's response to knocking from too low an octane can be to richen the mixture as well as retard the timing.

Nor am I suggesting that the quality of the BP fuel is worse than Shell. I think the difference can be adequately explained by the kv figure of the fuel that addo was talking about earlier - how easily does it flow under pressure. For a given fuel rail pressure and injector pulse width a fuel that flows more easily will flow a greater volume and therefore run slightly richer in open loop mode when the O2 sensor is not providing feedback to the ECU, and the difference is probably only a few percent.

It could be that the V-Power has more cleaning additives in it that have an effect on the kv of the fluid much like adding the injector cleaner clearly does - I'll bet that if I add a double dose of injector cleaner the performance will pick up, but not because its "cleaning" anything - it's just making the fuel mixture flow a bit more easily.

It's only because the engine is running so lean that small changes in flow rates cause a noticeable change in performance as the mixture passes the critical threshold from lean to rich. Under normal conditions under WOT in open loop mode the mixture should be "very rich" (on the order of 12/1 to 13/1) so changes of a few percent would make no noticeable difference to performance, therefore the difference between these two fuels would not be noticeable.

So I'm still sure that this lean running is the root cause of the lack of power and intermittent fluctuations in power, as small changes in mixture around stoichiometric under heavy load will affect performance quite a bit.

I'm still no closer to identifying why its running so lean - I tried loading the engine while the car is stationary today - in 3rd gear (snow mode) with the brake on then accelerating against the torque converter in the hopes of loading the engine enough below 2000 rpm to make it run lean and check the fuel pressure at the same time - no can do. The torque converter can't load it enough and the rpm goes up to about 2500 which is mostly out of the troublesome low rpm region. (I don't want to stress an already weary gearbox either)

To get it to run solidly lean the ideal conditions are 3rd gear, torque converter fully locked up, puttering up a hill at 1500 rpm - then even half throttle or less will see it running constant lean. Unfortunately that means to make any further progress in the diagnosis I have to rig my fuel pressure gauge to be safely viewable in the car while the car is being driven on the road...

I did post a message to "ScannerDanner" with some details asking some advice and direction in identifying this lean condition and whether it could be vacuum leak related (since its occurring at low rpm) or whether it has to be fuel related and in his reply along with a few suggestions of what to check he said in 20 years he "has never fixed a low power complaint by fixing a vacuum leak" and that a vacuum leak is usually only going to affect idle.

So that's good enough for me to rule out a vacuum leak as the cause of lean running under WOT. It would take a massive vacuum leak to have any effect at all at WOT and then it would be idling at about 2000 rpm... The car idles absolutely fine, especially when the O2 sensor is warmed up.

So I'm chasing a fuel problem, possibilities include:

* Low fuel pressure, (weak pump, low voltage to the pump, pressure regulator)

* Injectors that aren't flowing as much as they should due to deposit build up in the pintle valve (just because they're balanced doesn't mean their flow rates are up to the correct volume, they could all be balanced but at only 80% of normal flow due to deposit build up)

* Low voltage/current to the injectors

* An input problem to the computer causing miscalculation of fuel in open loop mode. (MAP, TPS, ATS etc)

It doesn't look like this ECU is able to learn any corrections for WOT so if any of the above are out by a long way the ECU is just going to fuel too lean in open loop mode without knowing that anything is wrong.

Testing the fuel pressure under WOT while driving while the O2 is reading lean seems to be the next logical step but physically trying to do that and do it safely is not easy.

[Mandrake]

Another update for those still following this thread. (Still there stevieb ? )

Over the weekend I made up a second back probe test lead to allow me to correlate TPS or MAP sensor outputs with the lean O2 reading under load during driving.

Some spare 3mm shielded mic cable, a couple of sewing pins and some heat shrink and I had a very nice test lead that can be left in semi-permanently with no risk of shorts etc:



The TPS passes a ramp test on the scope perfectly with no drop-outs or glitches, is perfectly proportional to movement and I could not see anything wrong with it at all while driving. Not surprising since its a new TPS but I doubt whether the original was faulty either.

Likewise the MAP signal is absolutely fine - fast responding, accurate, no glitches, its working absolutely perfectly to the best of my understanding of how a MAP signal should behave under different conditions.

So I can confirm 100% that during episodes where the engine is running lean (as reported by the O2 sensor) at low RPM under wide throttle that the MAP sensor is reading full voltage (eg no vacuum / maximum pressure) as it should be, therefore there is no possible way that the MAP sensor could be responsible for lean running at WOT as its already reporting maximum pressure, and the MAP reading is a primary input for determining fuelling.

At WOT the only factors that contribute to calculating injector pulse width are engine RPM, manifold pressure, (MAP) throttle opening, (TPS) engine coolant temperature and air input temperature. So out of those the only one that hasn't been conclusively ruled out is the air intake temperature sensor, (which I can't retest until I get my Lexia back) however I strongly doubt its the intake air temperature sensor as it has never shown any symptoms before of suspicious readings, so I think we can now pretty much rule out computer sensor INPUT's as the issue.

So we're now down to a relatively short list of suspects for lean running at WOT:

1) Sagging fuel rail pressure under high demand. (eg a weak fuel pump or poor electrical supply to the pump)

2) Lower than normal flow volume through the injectors. (Restricted injectors)

3) A problem with the electrical drive to the injectors (low voltage possibly from some sort of wiring problem - I know its not the ECU)

Let's look at them one at a time.

1) Sagging fuel rail pressure under high demand fits the symptoms perfectly, and the voltage at the pump terminals did seem a bit lower that I would like - sometimes dipping as low as 12.7 volts, however I remain suspicious that dropping to 12.7 volts from a maximum of 13.3 volts would cause such a severe lean condition when the pump should have something like a two to one margin in delivery volume and maximum pressure. It could be that if delivery is VERY marginal due to a weak pump, variations in voltage might have some effect and account for some of the variability of the symptoms but it wouldn't be a primary cause.

I replaced the fuel pump so it can't possibly be that, right ? Well.... I replaced it with a second hand one of the same age of unknown provenance... it came from the red Xantia V6 KP broke, but that was the same high mileage car (160k compared to 110k on mine) that I got a second hand coil pack from which later turned out to be faulty, so I have to face the very real possibility that I have replaced one old weak fuel pump with another old weak fuel pump that might even be worse than the original.

Quoted fuel delivery volume for the pump is 2 litres per minute at 3 bars - I tested my original pump and found it to be only 1.2 litres/minute at 3 bars, quite a large deficit, hence becoming suspicious of it and seeking a 2nd hand replacement due to the cost of a new one. I'm ashamed to say I did NOT test the volume delivery of the replacement pump before or after fitting it, due to the difficulty of doing the test by disconnecting the fuel rail when working on the side of the road. So I actually don't have any idea what the delivery volume of the pump that has been in the car for at least the last 6 months actually is...

2) Lower than normal flow volume through the injectors due to a restriction - the ones in the car now are second hand from an unknown mileage car, I tested and cleaned them as much as I could, they measure well balanced but the one critical test I can't do is measure absolute flow volume under known conditions - which is what the professional cleaners do with their graduated test tubes and access to flow volume specifications from the manufacturer. So they might be well balanced against each other but only achieving 80% of the necessary flow volume for example.

The flow wouldn't have to be hugely down to cause lean running either - if we assume the mixture should be 13/1 under WOT then a lean 15/1 mixture would only require a 15% reduction in flow volume... If the fuel pressure was a bit low due to a tired fuel pressure regulator spring that would contribute too. My original regulator only made 2.7 bars, (should be 3.0) the second hand one I got from Stempy made 2.9 bars, the one in the car now that came with the rail makes 2.8 bars, so it may contribute to the issue somewhat. (2.8 bars from 3.0 is a 6% reduction) I should have kept Stempy's regulator in the car...

3) A problem with the drive to the injectors is possible as well - low voltage will cause a shorter effective opening time and less fuel flow for the same pulse width, normally the ECU compensates for battery voltage variations (that's why the ECU measures the battery voltage) but if the problem is high resistance connections to the injectors it may not compensate for that.

So I think the next critical tests are a delivery test for the fuel pump fitted to the car at the moment to see if its worse than the original or not, and an under load pressure measurement to see if fuel pressure is sagging when the engine is going lean. The results of that test will decide where to go next. (Do I have a hunch ? Yes - I believe both my original fuel pump and the second hand replacement are weak)

If I can adapt a fitting for the click lock connector on the fuel filter and fuel pump then I'll be able to do both a volume delivery test and an on-the-move fuel pressure test relatively easy. To do that I'm going to order and fit a new fuel filter and use the spigots on the old filter to fashion some adaptors.

By the way the car has been quite sluggish for the last week, when I was connecting my test lead to the TPS and MAP sensor I had both sensors unplugged when I turned the key on to measure voltages etc, and also had the key on and off many times during my voltage testing without starting the engine, I think in the process I've inadvertently triggered an ECU reset, as the car is MUCH more zippy and responsive to the throttle immediately after that.

Despite that the engine was still running really lean under WOT for extended periods of time even when accelerating on the motorway, so I think the cause of low power is two fold - lean running, which is also the root cause, but in addition there is further power loss that occurs over time probably due to the knock sensor retarding the timing due to the engine knocking when running hot on a lean mixture. The ECU reset temporarily resets the timing maps so performance increases a lot but as it continues to run lean under some conditions it starts knocking and the timing goes back again especially prolonged running when the engine is fully warmed up.

[Mandrake]

PS has anyone had any dealings with Bosch fuel pumps for the Xantia ? This doesn't seem to be a bad price for brand new:

http://www.mister-auto.co.uk/en/fuel-pu ... 0!219.html" onclick="window.open(this.href);return false;

£62 compared to £162 + vat from Citroen...