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

[larppaxyz]

So I've decided that as well as the spark plug leads being dodgy, its high time I replaced the TPS.

Even when the engine has been otherwise performing perfectly with the swapped ECU and temporarily taped up spark plug leads, one problem has stubbornly persisted for months and has not responded to anything I've done - a big flat spot/hesitation just above idle.

The symptom is that the car will be idling perfectly, but if I tap the throttle just slightly with my foot it will stumble/hesitate and in fact nearly stall, with the indicated rpm dropping way down before it recovers.

It doesn't seem to exhibit this for the first 30 seconds or so after a cold start while the cold start enrichment is still active, but it does it at any other time whether partially or fully warmed up.

While driving its noticeable as a stumble / momentary cut out when accelerating from stationary, and it's sometimes noticeable in 2nd gear on take up from coasting.

If I hold the throttle very slightly above idle the rpm will drop and then start oscillating up and down. From all these symptoms I think I have a TPS with a dead spot in it where the wiper is loosing contact just above the idle position.

This. I have exact same symptoms (like we have been discussing before) still. Actually best way to "detect" if car is on that "crappy" mode is to test it with idle, holding throttle very slighty above idle.

When i watch my TPS values on diagnostics, they do look just fine. No skips or anything, but lexia has such a slow update rate that there could be some problems anyway. I already tried to "reposition" my TPS as it's possible to rotate it just a little. This however was long time ago and i had that crappy intake pressure sensor and glogged up ICV. So spraying it up with some electronic cleaner and so could help or not. After TPS sensor only sensors left unchanged on my car are CPS and knock sensor.

[Mandrake]

So I've decided that as well as the spark plug leads being dodgy, its high time I replaced the TPS.

Even when the engine has been otherwise performing perfectly with the swapped ECU and temporarily taped up spark plug leads, one problem has stubbornly persisted for months and has not responded to anything I've done - a big flat spot/hesitation just above idle.

The symptom is that the car will be idling perfectly, but if I tap the throttle just slightly with my foot it will stumble/hesitate and in fact nearly stall, with the indicated rpm dropping way down before it recovers.

It doesn't seem to exhibit this for the first 30 seconds or so after a cold start while the cold start enrichment is still active, but it does it at any other time whether partially or fully warmed up.

While driving its noticeable as a stumble / momentary cut out when accelerating from stationary, and it's sometimes noticeable in 2nd gear on take up from coasting.

If I hold the throttle very slightly above idle the rpm will drop and then start oscillating up and down. From all these symptoms I think I have a TPS with a dead spot in it where the wiper is loosing contact just above the idle position.

This. I have exact same symptoms (like we have been discussing before) still. Actually best way to "detect" if car is on that "crappy" mode is to test it with idle, holding throttle very slighty above idle.

When i watch my TPS values on diagnostics, they do look just fine. No skips or anything, but lexia has such a slow update rate that there could be some problems anyway.

Yes, the update rate of the Lexia is far too slow to detect a noisy/intermittent TPS, as is a digital multimeter. Only an oscilloscope would show it. I've checked my TPS with a scope before and couldn't see anything wrong, but that was a year ago, and the problem is intermittent after all. Only replacement will rule it out 100%.

I already tried to "reposition" my TPS as it's possible to rotate it just a little. This however was long time ago and i had that crappy intake pressure sensor and glogged up ICV. So spraying it up with some electronic cleaner and so could help or not. After TPS sensor only sensors left unchanged on my car are CPS and knock sensor.

So are you saying that you have already replaced your TPS, or that you haven't ?

Here is the TPS that I ordered for £14 if you're looking for one. Maybe I was lucky but it seems to be a genuine Bosch item even though it's not stated to be:

http://www.ebay.co.uk/itm/171133857705" onclick="window.open(this.href);return false;

As soon as I get a break in the weather during a weekend I'll be changing it over.

By the way, one thing that makes me suspect the TPS in regards to the engine speed oscillating up and down with a constant throttle just above idle is that if you unplug the TPS you will find the engine will still try to run (using only the MAP reading) however at a constant throttle opening (almost any throttle position) the engine speed will keep oscillating up and down in the same way.

This suggests that the TPS wiper arm is going open circuit at the exact spot just above idle where the rpm oscillates, as it does it at any throttle opening when the TPS is unplugged! Try it and see...

[larppaxyz]

So are you saying that you have already replaced your TPS, or that you haven't ?

No, i have not tried to replace it.

Is it hard to remove? Can i just pull it out without taking whole throttle butterfly apart? It's already snowing in here

[Mandrake]

So are you saying that you have already replaced your TPS, or that you haven't ?

No, i have not tried to replace it.

Is it hard to remove? Can i just pull it out without taking whole throttle butterfly apart? It's already snowing in here

Depends how much room you have to the right hand side of it in the 406.

It's held on by two torx head screws, one above one below. On the Xantia its right next to the LHM reservoir tank so there is barely any room to even get a right angle drive onto it.

I tried to remove mine without removing the manifold and LHM tank but was unable due to the bottom screw being seized, so I'm going to have to take the manifold out on mine to replace it...

But if you have good access to those two screws try them to see if they come undone easily if so you should be able to do it in place.

[Mandrake]

Still waiting for a fine weekend to swap the plug leads and TPS over.

The plug leads I was waiting on were finally "found" on Thursday when I got tired of waiting for a delivery that should have arrived by Tuesday and looked at the tracking information on the website - signed for on Tuesday by someone whose name I didn't recognise. The package was finally found 6 houses up the street!! Apparently the Royal Mail driver had seen someone come out of their front door and called them over to take the package, despite the fact they were 6 doors away from us and the neighbours on either side of us were home... Lazy bugger...

Meanwhile I'm still suspicious of my ECU as a contributor to my engine problems. About a week ago the car was (with the taped up spark plug leads and top cover off, as it still is now) running very nicely on David's ECU, I swapped mine back under the assumption there was nothing wrong with it and the performance immediately dropped a lot. I gave it a few days of driving to see if it improved thinking that maybe it would take time to adapt to the octane of the petrol (I'm running it on 99) but although it did improve slightly after a few days it was still quite lacking.

Yesterday we were out driving quite a bit in the wet rainy weather and I really noticed it - the engine was running very smoothly but just lacking in oomph and pick-up especially low down. It was particularly noticeable that when revving the engine under load that its very quiet and smooth and the engine note sounds more like a kitten than a tiger. In other words it felt and sounded like its running on retarded timing again.

So yesterday I swapped the ECU back to David's again while the car was already warmed up and performing very sluggishly and there was an immediate large improvement. I did about the same mileage on that ECU again as I'd done on the first one and the performance stayed very sharp and responsive. It just feels so much more eager even with a light throttle, and picks up really well at low rpm. Accelerating under load at higher RPM it sounds a bit more like a tiger than a kitten now...

This morning it started easier than it has been on my ECU and acceleration was instantly sharp and responsive even with a cold engine. Assuming it stays good for a few days then sadly I think there is something wrong with my ECU. I'm not sure what exactly, but it feels a bit like the timing is getting retarded so maybe there is a problem with the knock sensing and timing control part of it...

I'll have to keep my eyes peeled for an ECU next month I think, they're quite rare at reasonable prices, I did see one listed for about 70 euros last month but its probably gone by now, however they do seem to turn up from time to time if you look hard enough. (And of course an ECU off a scrapped car is an option, provided the matching CPH is available and the confidential code is known - I've already proven I can program my keys to work with a different CPH)

I still think the TPS is faulty as well - this morning after driving to the train station with the engine pulling and running really well and a perfectly smooth idle, if I give the throttle the slightest flick off idle it stumbles and tries to stall, just like it was on the other ECU. It wouldn't surprise me AT ALL if I find that I've been dealing with multiple faults all along...

[Mandrake]

There's definitely a difference between the two ECU's - I just confirmed again tonight in a 7 degree cold start that with David's ECU the engine catches and fires instantly on the first revolution even with a cold engine, whereas with my ECU when the engine is cold it takes many revolutions of the engine before it catches, about half a second to a second worth of cranking before it fires...

I wonder what would cause that...?

[Hell Razor5543]

Failing solder joints? (I do mean inside the ECU casing).

[Mandrake]

Failing solder joints? (I do mean inside the ECU casing).

Although I didn't tell anyone I've actually had my ECU apart a few weeks ago and carefully re-soldered all the output drivers, the main connector pins and anything else that looked like it needed it. There were a few that looked slightly cracked and potentially dodgy but there was no change at all - no better or worse. If it has a fault its not dry joints.

Dried up filter caps allowing noise into the knock sensor input circuit maybe ? That's about all I can think of, although it only appears to have one significant sized electrolytic cap in the whole ECU.

ECU board top side:

https://dl.dropboxusercontent.com/s/57w ... 9%20pm.jpg" onclick="window.open(this.href);return false;

Bottom side:

https://dl.dropboxusercontent.com/s/rck ... 6%20pm.jpg" onclick="window.open(this.href);return false;

[addo]

Looks like October 98 production for that ECU.

[Mandrake]

Looks like October 98 production for that ECU.

Close. The warranty start date is 1st August 1998 and from memory the ECU manufacture date reported by the Lexia is June 1998. David's ECU is early (Feb ?) 1999 according to the Lexia so is some 6-8 months newer.

Was there a hardware revision of the ECU at some point ?

[addo]

When this thread hits 100 pages we need a party. Everyone getting on Skype and revving the tits off their Xantia?

The front view of the PCB shows in one corner, an "8" with ten dots in tow rows - six, plus four. I read that like the glass manufacturers' markings - the tenth month of 1998.

So quite probably, you have a replaced, unlocked ECU flashed with the original generation software - maybe even the original calibration files.

[Mandrake]

100 pages is nothing addo, the audio forum I frequent has many many threads that are well in excess of 100 pages - threads not instigated by me I might add, but I've certainly contributed to them and kept stirring the pot...

I'll double check the firmware versions and manufacturing date of both ECU's next time I have the Lexia on it. I've looked at them before but didn't think to save a record.

I think I'm getting close guys, we might not actually hit 100 pages... Tonight the weather has swung from damp and wet to very dry, and with a combination of the dry air and the loaner ECU the car is going like an absolute rocket tonight. Very very grunty, just how I remember from when I bought it.

There's got to be a connection with the dry air and it running well - eg high voltage leakage from the spark plug leads/boots in damp air.

The stumble issue is interesting - despite going like a rocket tonight the stumble just off idle is still there which makes me think it is an independent problem, and hopefully the TPS.

I tried to catch a video of the stumble this morning - it might be a bit hard to hear unless you listen with headphones. All I'm doing is basically tapping the throttle lightly but quickly with my foot, hardly depressing it at all and you can hear and see from the tacho that the engine is trying to stall. Near the middle of the clip I floor it a couple of times and the first time it stumbles there too. Near the end of the clip I tried to lift the rpm slightly which sometimes results in the rpm hunting up and down but I couldn't get it to do it this time.



Outside air temp was 6 degrees at the time and coolant temperature was about 60 degrees.

larppaxyz: does yours do this too if you quickly tap the throttle ?

[larppaxyz]

larppaxyz: does yours do this too if you quickly tap the throttle ?

Not quite like that, but thats exactly what it does sometimes when i'm just idling.

Now that i have been thinking this TPS issue (and watched some youtube videos about TPS problems and reading some articles) i think my lower end (idle part) of TPS is open circuit most of the time and ECU detects this and ignores or calibrates TPS more or less randomly because of this. I haven't seen any error codes about TPS, but maybe they get clearead everytime ECU detects TPS is ok again, or maybe it's not bad enough to trigger code.

Anyway, it's 5min job max to replace TPS on my Pug, but i have no quick access to (new) replacement part. I'm thinking about opening up my TPS (i know it's glued/molted, but should be possible anyway) to clean it and just slightly twist those "legs" that are in contact with "resistance" part. I will do some resistance measuring and visually inspect it. I assume construction is similar to this http://www.4crawler.com/4x4/CheapTricks/TPS/tps2.gif" onclick="window.open(this.href);return false; (this is however 4-wire version).

I don't know why, but i have feeling this could be it finally (Yeah... right)

[lexi]

the audio forum I frequent has many many threads that are well in excess of 100 pages -

That'll be DIY Audio where obsessive students argue about "the sounds of cables" and full range drivers with Enabled dot patterns on them?

[Stempy]

Don't get him started.....