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

[Mandrake]

Thanks Richard,

Thats that ordered now.

In other news I fitted the new MAP sensor this afternoon in between the rain showers, and it didn't work. The engine just would not start at all. With a sinking feeling I went to get the Lexia and sure enough, the new sensor is DOA. Not only did it immediately have a "pressure sensor coherence" fault logged, the live reading from the sensor was duff - reporting 130mb with the engine turned off...in fact when I plugged the sensor in while watching the Lexia the reading gradually crept down from ~900mb to about 130mb over a period of a minute or so, all with the engine not running.

To say this is a let down is an understatement. Now obviously I need to get it replaced or refunded but in comparing the two sensors I'm concerned about the quality of the £20 replacement as well, not just the fact it is DOA. The original is Bosch branded and has a taper inside the tube that reduces to a pinhole size hole through into the main sensor body, however the replacement (with no brand printed on the actual sensor) has a big wide hole into the main body of the sensor with the sensor chip and wiring all plainly exposed. I've attached a picture:

What are peoples thoughts on this difference ? I'm inclined to ask for a refund and go elsewhere rather than ask for a replacement, but I'm not sure at the moment. My worry is that all the £20 MAP sensors will be the same knockoff design, with genuine ones up around the £65 mark.

Nothing is ever easy is with this car is it!

[addo]

Your sensor rail voltage remains correct at around 5V?

[oneday]

i think looking at the quality of that one i would bite the bullit and pay the money. has anyone got a known good one you could try before you spend out on one.

[Mandrake]

Your sensor rail voltage remains correct at around 5V?

If you mean the 5 volt supply to the sensor, I didn't have time to check it (had to get the car working again to go out shortly) but I see no reason to believe that there would be a problem with the 5v supply from the ECU. The original sensor is back on again and working fine and gives believable mb readings on the Lexia. Pretty sure its just a DOA sensor addo.

[addo]

Got to say, I have had nil power delivery issues since addressing the exhaust restriction on my 16V motor. It's highlighting some line pressure irregularities in the gearbox, but I'm hoping a solenoid change will see them fixed. Fuel usage has gone up because I'm not using compression braking (due to the trans symptoms) and probably zooming about a bit more with the excitement of it.

[Mandrake]

Is that a 2 litre 16 valve with an AL4 ?

What sort of loss of power characteristics were you noticing due to the exhaust ?

[addo]

Yes, an AL4. Firstly, I had a sensation of "sogginess" that came and went for several years - laggy response when the foot was pressed down, more especially with a load in or behind the car.

Then, from late 2011, a growing tendancy to overheat and struggle a bit when loaded up and pulling hard. Also a slight rattle of the exhaust innards near the motor on cold starts. I checked and rechecked both fans on several occasions to dispel ideas the fans were helping me overheat.

Finally, six weeks ago a significant loss of oomph - it still came and went - that reduced my towing speed uphill to about 40km/h with a trailer, and gauge temps trended upwards of 105°C (indicated). A new exhaust joint hardware kit (£8 pattern part) and a visit to Mr Prybar's Muffler Services saw the restriction sorted. The front half of the cat had formed chunks and powder that restricted gas flow through the second "block" of catalytic material.

[Mandrake]

Does sound very familiar I have to say... Everything except for overheating and rattle of the exhaust. I don't do any towing mind you, and the V6 probably has enough extra oomph in reserve that a power loss is not as catastrophic as a 2 litre.

I presume "Mr Prybar's muffler services" replaced the cat with a straight through pipe ? I'm not sure the MOT man would appreciate that over here, I would have to replace the cat with a "kitten", since a genuine cat would be 3 times the value of the car...

[addo]

There is a rumour that some cunning devils install a 2" 304 stainless straight pipe through the middle of the cat, and weld the tail back on.

[CitroJim]

Simon, sorry to hear the new MAP sensor was a DOA

Hope you can get it replaced with no problem...

[Mandrake]

Simon, sorry to hear the new MAP sensor was a DOA

Hope you can get it replaced with no problem...

Do you see any problem with the hole size and the exposed chip inside though ? If not I'll get the seller to replace it rather than refund.

[CitroJim]

It being so wide open like that is not how I've seen them in the past Simon, all have had quite small holes...
I'm wondering if your duff one was badly made and is leaking and therefore unable to measure accurately...

[Mandrake]

I thought the wide open hole was odd too, hence my concern. From what I understand the method of operation is the small chip that is visible is a solid state strain gauge - the top side is exposed to the manifold pressure, the bottom side has a small sealed cavity of air as a reference, thus changes in pressure on the top side apply strain which is measured.

If the sealed air cavity had a leak it wouldn't work, although its just as likely to be an electrical fault. There is no difference in the mb reading on the Lexia with the engine off or cranking...

The original has a pinhole that is maybe 0.5mm at most, presumably to protect the circuitry inside, on the other hand oil contamination could easily block that small pinhole hole causing sluggishness in response since the oil droplet would have to move with pressure change...

[addo]

Mine - a Bosch, and the original sensor - has no variance in the bore; it is a straight hole.

[Mandrake]

Mine - a Bosch, and the original sensor - has no variance in the bore; it is a straight hole.

As big as the one shown in the picture with visible insides, or about 0.5mm ?