Xantia HDi power gremlins

[Rhothgar]

Morning Wheeler,

Have tested the EGR with a vacuum gauge and can clearly hear it dropping shut when the pressure is released.

Also, done all the visually checks on the pipes and smoke tested the turbo pipes and no leaks manifested themselves.

I did buy a gasket for the inlet manifold as at 205000 I’m assuming it’s well clogged up but that would not affect pressure just volume, surely?

But then with a lower volume of air the ECU would try and reduce the injection cycle and maybe it is so restricted that the ECU simply cannot adjust the injection down that low perhaps?

Or is it actually pointing to the turbo waste actuator being stuck or perhaps a perforation of an internal diaphragm or the metal casing? Is that a possibility?

Just got an email from AUTODOC today offering free delivery! I hate doing it but it’s tempting to order those parts.

I’m sure one of my neighbours have me a working Lexia late last year so I’ll have a dig around for that and do the test you suggest.

I did scope the new MAF meter to see if it was in range and it looked fine-ish.

If the figure does alter when EGR pipe removed what does that indicate please?

[Rhothgar]

OK. Been going through some videos from August last year.

It is clear that the inlet air flow is always higher than the air intake reference value by some considerable amount despite something preventing the turbo making full boost pressure.

Here’s a photo of the P0246 code I get when I go on a steady run of say 30 miles on the motorway and later into a journey if I say come out of a roadworks at 50mph and out foot down to get back up to 70mph it then tends to throw a fault when the foot is down for an extended period.

It is like it takes its time to realise there is a fault in boost.

https://share.icloud.com/photos/0bdZKtH ... _PssP5hBgw

[darbuck]

Hi Roger, check your solenoid valve for the turbo actuator is working and plumbed correctly. check all vacuum and turbo hoses are in good condition there could be a leak preventing full boost which may be unrelated to the smoke. The black smoke is more likely a fuel air ratio issue, over fueling possibly a leaking injector or not enough air intake. Have you changed your air filter recently? Could be clogged. have you done a leak off test. Do you have high blowby? What engine does your xantia have?

[Rhothgar]

Hi Roger, check your solenoid valve for the turbo actuator is working and plumbed correctly. check all vacuum and turbo hoses are in good condition there could be a leak preventing full boost which may be unrelated to the smoke. The black smoke is more likely a fuel air ratio issue, over fueling possibly a leaking injector or not enough air intake. Have you changed your air filter recently? Could be clogged. have you done a leak off test. Do you have high blowby? What engine does your xantia have?

Hi Darbuck.

Not sure if the valve is but...

Underboost can be created by a stuck wastegate. Perhaps it is fully stuck open. I'd imagine a boost of 30% is probably still possible with a fully open wastegate and if not maybe it's not fully open.

I need to get under the car and take the pipe off of the wastegate, then actuate the lever and see if it holds pressure with my finger over the end of the wastegate pipe (which goes back to the solenoid) on the actual wastegate itself. I need to check the actuation of the lever to see if it is seized or not free moving.

Have vaccum checked all tubes previously but it is not really the best way to test a rubber tube as the suction might actually seal a split (but not a hole). Changed air filter back in November from memory. Did a leak-off test years ago and I think it wasn't particularly brilliant then. I will do another.

It's the 2.0HDi.

[darbuck]

A pinhole coul cause a drop at higher RPMS, that's the first dw10 engine isn't it . If so the actuator does give trouble on them. I remember having boost problems on my MK1 C5 with that engine and it was a combination of a bad hose and solenoid.i just replaced all the hoses to rule them out for the sake of a couple of euros it was worth it. The hoses are over twenty years old now so they could be porous if they haven't been changed.

[Rhothgar]

A pinhole coul cause a drop at higher RPMS, that's the first dw10 engine isn't it . If so the actuator does give trouble on them. I remember having boost problems on my MK1 C5 with that engine and it was a combination of a bad hose and solenoid.i just replaced all the hoses to rule them out for the sake of a couple of euros it was worth it. The hoses are over twenty years old now so they could be porous if they haven't been changed.

I am thinking the pipes MUST be sound otherwise if you had a pinhole then it wouldn't hold vacuum to the wastegate which would surely mean it would overboost. Yes. It's the DW10 engine.

Unless vacuum keeps the wastegate shut but that is the exact opposite to how I understand it works and I doubt the principle has changed.

[wheeler]

Morning Wheeler,

Have tested the EGR with a vacuum gauge and can clearly hear it dropping s**t when the pressure is released.

All this really tests is that the valve itself works, remember the valve is dumb & its controlled externally with vacuum via the electro valve & ECU.

If the figure does alter when EGR pipe removed what does that indicate please?

In this case now nothing as the Idle air flow is too high to begin with. I wouldnt expect anything to change in this case as i suspect the EGR valve is already closed. If you have 500 mg/cp @ idle that says to me the EGR valve is remaining closed. However as you are saying you have a vacuum gauge you could do the test in reverse. Remove the vac pipe from the EGR valve & plug it with a small bolt or similar, connect your vaccum gauge to the EGR valve with the engine idling, open your EGR valve with your vacuum gauge & if the valve is working you should see the airflow reading drop down to somewhere in the 200-300 range.
If i was working on this car i would initially be focusing my attention on the vacuum side of things as its a common link between the EGR valve not operating & a boost fault.
Many years back i was fault finding on a Xantia HDi with a boost issue & it turned out some of the vac pipes going to & from the electrovalves etc were blocked up with a hard carbony type material, when compressed air was blown through the pipes all this black dust came firing out, that solved the issue, taken me ages to find that.

PS is this a 90bhp or 110bhp? 110 bhp models also have a vac operated EGR throttle butterfly in the intake make sure thats not closing when its not meant to

[Rhothgar]

Morning Wheeler,

Have tested the EGR with a vacuum gauge and can clearly hear it dropping s**t when the pressure is released.

All this really tests is that the valve itself works, remember the valve is dumb & its controlled externally with vacuum via the electro valve & ECU.

If the figure does alter when EGR pipe removed what does that indicate please?

In this case now nothing as the Idle air flow is too high to begin with. I wouldnt expect anything to change in this case as i suspect the EGR valve is already closed. If you have 500 mg/cp @ idle that says to me the EGR valve is remaining closed. However as you are saying you have a vacuum gauge you could do the test in reverse. Remove the vac pipe from the EGR valve & plug it with a small bolt or similar, connect your vaccum gauge to the EGR valve with the engine idling, open your EGR valve with your vacuum gauge & if the valve is working you should see the airflow reading drop down to somewhere in the 200-300 range.
If i was working on this car i would initially be focusing my attention on the vacuum side of things as its a common link between the EGR valve not operating & a boost fault.
Many years back i was fault finding on a Xantia HDi with a boost issue & it turned out some of the vac pipes going to & from the electrovalves etc were blocked up with a hard carbony type material, when compressed air was blown through the pipes all this black dust came firing out, that solved the issue, taken me ages to find that.

PS is this a 90bhp or 110bhp? 110 bhp models also have a vac operated EGR throttle butterfly in the intake make sure thats not closing when its not meant to

I've just noticed the typo for dropping shut! I've now amended that for clarity.

So, to reiterate as my earlier post said dropping s**t!!!, I can hear the valve drop shut when the pressure is released. Would you still suspect the EGR in the case? Could it be coked up and not fully closing? Would that cause this fault?

OK. So if I apply vac directly to the EGR if I can access it easily enough then if it drops, that proves the fault lies elsewhere. So if it doesn't drop then what?

Mine's the 110 HDi. I have seen that butterfly and I think that might come off the solenoid valve nearest to the throttle position sensor from memory. I did map this all out in a video.

So when you say "make sure that's not closing when its not meant to", when is it supposed to be open and when is it supposed to be closed please? Sounds like if that is wrong it could choke the boost a little.

Maybe a daft question but that is in the flow so how do you check it's operational if you cannot see it because surely you need to leave the induction pipe in place otherwise it won't receive the turbo pressure?

Thanks in advance, Wheeler. You're an absolute gem.

[wheeler]

Just to be clear I do not think the EGR is at fault here, I just suspect that it is not operating, This itself would not cause the car to loose power, in fact if the EGR valve is not opening i would expect it to have a bit more power if anything, the EGR valve deliberately strangles the engine.
The test will tell you that the MAF is reading correctly & that the EGR valve itself (not the controlling of it) is working correctly.

What im getting at is that the EGR valve is not operating & there seems to be issues with boost operation/wastegate control. Both both of these units need vacuum to operate correctly. Closer look at the vacuum system are you getting good suction at the pump & at the 'supply' sides of the 3 electrovalves?

As for the butterfly yes i should have been more clear, yes you cant see it so check that the spring return is nice & tight & that it springs fully open when its released. It should be fully open when the car needs power, it normally fluctuates between open & closed at idle. you can rule it out by disconnecting the vac pipe & plugging the end of the pipe, the butterfly should then stay fully open.

[Rhothgar]

Right. I’ll read your reply in full when I get in front of PC again.

However, I have just taken EGR pipe off and on car scanner app it increases from the usual 13.5g/sec at idle to 16.6g/sec.

[Rhothgar]

Just to be clear I do not think the EGR is at fault here, I just suspect that it is not operating, This itself would not cause the car to loose power, in fact if the EGR valve is not opening i would expect it to have a bit more power if anything, the EGR valve deliberately strangles the engine.
The test will tell you that the MAF is reading correctly & that the EGR valve itself (not the controlling of it) is working correctly.

What im getting at is that the EGR valve is not operating & there seems to be issues with boost operation/wastegate control. Both both of these units need vacuum to operate correctly. Closer look at the vacuum system are you getting good suction at the pump & at the 'supply' sides of the 3 electrovalves?

As for the butterfly yes i should have been more clear, yes you cant see it so check that the spring return is nice & tight & that it springs fully open when its released. It should be fully open when the car needs power, it normally fluctuates between open & closed at idle. you can rule it out by disconnecting the vac pipe & plugging the end of the pipe, the butterfly should then stay fully open.

OK. Cool. I will plug it and take it for another spin to see if it boosts correctly. It's easy to ignore that solenoid below the MAF sensor!

I did ensure all pipes were clear back in August 2023 IIRC but I can certainly check that again. It doesn't harm.

Interestingly, I've started using CoPilot Beta AI on Windows for any answer that I struggle to find on the internet.

I've been trying to work out the correlation between mm/cp and g/sec.

This is what mg/cp means according to AI:-

The term “mg/cp” in French automotive specifications typically refers to “milligrams per stroke” (milligrammes par coup), which is a measurement used to quantify the amount of a substance, such as fuel or emissions, that is emitted or consumed with each stroke of the engine. This term is often used in the context of emissions to describe the amount of pollutants, like NOx or particulates, emitted by the vehicle’s engine per cycle.

So if I see 13g/sec at 820rpm idle and am seeing 42.8g/sec at 1970 rpm then I wonder if it correlates as follows:-

13000mg/sec in 13.66 revolutions per second but because the engine is 4 stroke we divide by 2 to give 470mg/cp?

or 42820mg/sec in 32.833 revolutions per second divided by 2 gives 652mg/cp?

Am I clutching at straws with these calculations to convert g/sec back to mg/cp?

If I have found the correlation then it should be showing about 6.5g/sec at idle and then I thought of AI again and this is what is says:-

The correlation between “mg/cp” (milligrams per cycle) and “g/sec” (grams per second) involves converting the mass emitted per engine cycle into a mass flow rate. To establish this correlation, you need to know the number of engine cycles per second, which depends on the engine’s RPM (revolutions per minute). Here’s the general formula:
g/sec=((mg/cp)/1000?)×cycles per second
To find the cycles per second, you would divide the engine’s RPM by 60 (since there are 60 seconds in a minute). For a four-stroke engine, remember that it takes two revolutions to complete one cycle, so you would further divide the RPM by 2.
For example, if an engine operates at 3000 RPM, the cycles per second would be:
cycles per second=3000/(60×2)RPM? = 25 cycles/sec
Then, if the emission is 10 mg/cp, the conversion to g/sec would be:
g/sec=((10 mg/cp)/1000?)×25 cycles/sec=0.25 g/sec
This is a simplified example, and actual calculations would need to consider the specific engine characteristics and operating conditions. For precise conversions, consult the vehicle’s technical specifications or a professional engineer

[Rhothgar]

“disconnecting the vac pipe & plugging the end of the pipe, the butterfly should then stay fully open”..

But, humour me here, is the spring strong enough on the butterfly to keep it open when the turbo is on full boost?

If so, I can disconnect, plug and go for a drive to see if that resolves. Then presumably that narrows it down to the solenoid on the butterfly.

But how would this lead to poor fuel consumption? Would it be because the butterfly throttle is partially closed? This is what I don’t understand.

I assuming perhaps wrongly that the vacuum to the butterfly throttle actually closes the throttle. So if the vacuum is not sufficient it would allow boost. I will go back and reread what you have written again to make sure I’ve not missed something. I forget very easily after reading something at the moment.

[wheeler]

Yes mg/cp = mg per stroke. This is the only air flow measurement im used to & would have no idea how to convert it.

[Rhothgar]

Well that didn’t go well.

Just removed pipe and blocked it. However, there doesn’t seem to be a way to disconnect the pipe from the butterfly valve but ONLY at the solenoid valve.

So I removed from there and plugged the pipe but had no way of blocking the solenoid connection. Could do with the diesel leak-off cap.

So took it for a spin and th here’s even less boost obviously because the vacuum circuit is open. Threw a P0243 code. Wastegate makfinction. From this, I suppose we can assume that when the vacuum system is sealed the turbo wastegate is clearly working OK.

[wheeler]

The pipe100% just pulls off the butterfly.
You could just remove the vacuum ‘supply’ from the solenoid & block it there.
Alternatively you could just clamp the pipe with a brake pipe clamp etc.
Again you can run the engine with this butterfly pipe disconnected & blocked and the car will never throw up a fault or warning lamp about it.