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156 2.4 20V JTDm - Erratic Sooting / Smoking

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#1 · (Edited)
156 2.4 20V JTDm - Erratic Sooting / Smoking -> SOLVED

Hi to everyone!

I recently bought myself a 2004 156 SW 2.4 JTD 20V M-Jet Facelift II. So far so good, the only problem is that the car has a strange, rather erratic sooting behaviour: Sometimes it’s smoking like hell, sometimes not at all and this even in more or less same driving situations and comparable environmental conditions.

At first I assumed that the previous owner was always creeping around town in very low revs, which could have caused soot build-up in the exhaust systems. Then I’ve have tried using “Diesel Soot Stop” additive from Liqui Moly for a while in combination with – almost daily - higher rev driving on the motorway (3000-3800 rpm) for a few minutes.

Further I have visited a friend of mine who has an Alfa specialized garage… We checked all the known suspicious parts like turbo hoses, recorded graphs of different sensor data (Air mass set/actual comparison), water temp, etc. and everything was looking good. We didn’t check the AGR though, as it was already cleaned 6000 miles ago. However as soon as I have some time, I will also check and clean the AGR again.

I’ll try to give you an example of why the smoking behaviour seems so odd to me:

Driving for 35mins with an average speed of 80 MPH on the motorway, afterwards I take an exit where I’ll slow down to about 35 MPH. Then I’ll accelerate to 70 MPH (~80% throttle) from 2000 RPM in fourth gear and this is when the car is smoking badly (easily viewable in the rear view mirror in daylight). It’ll keep sooting all the way up to 4000 RPM, but it doesn’t seem to loose any power.

Then I’m driving in city environment (low rev) for another ten minutes until I’ll boot it (100% throttle) from 2000 to about 4000 RPM again – however in third gear – but this time there is no visible smoke at all!

Ok so then I though maybe it’s really soot build-up from driving with 2200 RPM on the motorway, however this morning I tried clearing her throat just before taking the exit by shifting into 5th and even 4th gear for a few mins, yet I had still the exact same smoking when accelerating on that exit. :rant:

So do you guys have any idea how this is possible or explainable? I’m thinking that maybe the AGR is too slow in certain situations which could explain the erratic smoking?

I happy for every advice as its not easy diagnosing it with that snatchy behaviour… Some days I think it’s all good, the next one I’m almost ashamed to accelerate harder. :cry:

Thank you in advance for all replys! :thumbs:

Greetings from Switzerland!
Marco-Antonio
 
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#2 ·
I think you're looking for non existing problems here... :)
If the car feels/drives fine what do you care if it smokes?
+ it's normal to have a bit of visible smoke on hard acceleration
 
#3 ·
Thanks for the reply! I know that diesels smoke to some extent, especially as it as no DPF...

But I thought (and heard) that the m-Jet models in combination with the VGT shouldn't be smoking so hard that it 'fills' the view through the rear windows during daytime? If I'm driving at night it looks even worse xD

I wouldn't complain if it’s only smoking to some - hardly noticeable - degree, but I don't like laying smoke screens... Specially as the car is NOT chipped or mapped!

Marco-Antonio
 
#4 ·
Have you ever driven a diesel before or is that your first one? Smoke at night always looks worse... I assume it's black smoke right?
I cannot judge exactly how bad is it from what you write...
regarding mapping...it is not always the case a remap makes the car more smokey...
 
#5 ·
Have you ever driven a diesel before or is that your first one? Smoke at night always looks worse... I assume it's black smoke right?
I cannot judge exactly how bad is it from what you write...
I have driven diesels before, however this is the first one that I personally own.

The smoke has actually a more grey/brown foggy look to it, definitly not thick deep black soot. I thought grey means it's not as rich as when it's black..? :confused: However it definitly doesn't look blue or white to me.

Regarding the intensity, I can still cleary see where I accelerated after I stopp accelerating further (3-5 seconds later) in the rear view mirror.


regarding mapping...it is not always the case a remap makes the car more smokey...
Yes very true, atleast if the mapping was done by people who know their stuff. I guess I was more thinking of Powerrail etc... :p
 
#6 ·
My 20v smokes abit only when I push it hard to 4000rpm in say 3rd but I would say that was normal , I would take the egr valve apart it's a easy job ! If the car has been used on alot of short trips it has been known to soot up badly . I've also found that since running her on v power it has had less smoke out the back .
 
#7 ·
They do seem to be a pretty smoky engine and mine blows out a fair bit when first booted after slow driving. The soot is unburnt fuel so if your fuel economy and power is OK (eg 40-45 mpg for mixed driving) then there cannot much wrong. My EGR and inlet manifold was pretty sooted up but then cleaning them made no difference to the amount mine smokes :)

Keith
 
#10 ·
I got close to a true 50 mpg (the computer claimed 63 mpg) with 5 in the car on the motorway to and from Blackpool running at 70-75 mph on the cruise control. The worse I have had is 38 mpg with the first tank full which entailed lots of town driving and 'fun' blasts. Its always hard to compare mpg figures given the influence driving style has but maybe yours has a minor problem such as a small leak on the intake side?

Keith
 
#9 ·
mate I have a car of the same generation albeit a 1.9 m-jet and honestly it smokes like a bapstard! its flipping mental.

honestly you would think that it had been really heavily remapped the wap it smokes is like a WWII tank.

I tell you what a wise mechanic friend of mine told me:

"it isn't about how much it smokes, its about whats in the smoke!"

meaning its about C02 emissions not about how much soot is in it, so don't even worry about it. if it aint broke don't fix it, honestly they just smoke.

my brothers citroen C2 1.6 HDi (remapped) also smokes like hell. he recently, at the advice of the same wise mechanic friend, ran some forte diesel engine treatment through his car and he thinks that helped with the smoking. I put some of that in mine last night with £20 of juice so will see how it goes but honestly don't worry about it!
 
#11 ·
Ok, so I checked the EGR valve yesterday and it had quite some soot build-up, however it was still opening and closing correctly. I also found out that the garage from the previous owner already mounted the EGR plate.

However what I also noticed was that three of the four screws were tightend very hard, except for one which felt kind of weak. The loose screw had some kind of teflon tape on it :wow: Now when I mounted it back I wasn't able to tighten that screw very much. I think it's the thread that's stripped :cry: :mad

In my view this is pretty bad, as it could loose boost through that gap that is not fully sealed with that one screw not beeing tight enough. What do you guys think? And what are my options?

I dont think that drilling the M6 thread to M8 would be a good idea, and honestly I'd rather not dismount the inlet manifold.
 
#17 ·
Ok so I exchanged the screw to a new one as its thread was also damaged. Now I was able to tighten the screw a bit more, but still not as good as the others. However I didn't notice any loss of power or anything on the drive to work today. Can I assume that this will be enough to not loose any boost? I can't imagine that the boost would be high enough to be able to leak through...

@TOX1C

Yeah I saw that Forte Diesel Treatment is recommended in multiple threads while searching the forum. I must try to get a hold of it here in Switzerland. But wouldn't such additives only work as long as you're using them or should FDT have long-term effects?

Thanks for the replies!
 
#18 ·
I think I need some further advice... I can't seem to loose the impression that the power below 2000 RPM is too low sometimes (low throttle response) and I'm thinking that maybe this also benefits the soot build-up, which I'm blowing out at higher RPM later. Yet from 2000 RPM (sometimes also 2200) I can clearly feel the boost kicking in strongly.

While cleaning the EGR I also took a look at how the VNT is working: If I start the car the actuator pulls the VNT mechanism back in approximately 3 seconds. If I turn it off it goes back slowly in about the same amount of time, which both sounds right to me...

Then I repeated the procedure again and the next few tries, while turning off, the rod didn't release properly until it slid back fast with a "pfffffft" sound. I'm guessing that something could be leaking, either the actuator itself or the vacuum pipe?

I'm imagining that sometimes the actuator isn't able to produce enough vacuum under load so that the VNT is in a slightly off position? I also had a P1238 but never saw the MCFS light come on though...

Thank you in advance for any advice!

Greetings Marco
 
#19 ·
I have the same issue with my 20v.

sometimes I can see the soot in my back window, sometimes I cant.

Like you I haven't found a solution yet.

From what I understand soot/smoke is caused by the wrong air fuel fixture (not enough air/too much fuel)
Often caused by a boost leak, or a sensor reading incorrectly and causing the car to inject too much fuel.

I thought mine was leaking from the egr, so I made a sandwich plate to completely block it off.. hasn't really made much difference.
 
#20 ·
I have the same issue with my 20v. [...]
'Glad' to have found someone who has the same problem. Never found any thing about erratic sooting behaviour anywhere before...

Yesterday morning on that same "reference" exit it blew out unusual loads of crap, so much that I wasn't able to see the cars behind be (with daylight!). But then after 5 minutes of city driving I tried accelerating hard again and nothing at all again.

While blowing out the EGR with compressed air I was thinking that the soot dust looks exactly the same in colour and consistency as the soot that's exiting my exhaust. So I'm sure that the greyish foggy soot is mostly old residues that get blown out at higher revs, while black smoke - which I don't really have - must be 'fresh'.

Now in conjunction with a very noticeable power loss below 2000-2200 RPM I’m starting to think that maybe the VGT/VNT (whatev') is somehow loosing vacuum, which causes the VNT to be forced back to max flow at low revs under load. This would then generate soot which builds up as the exhaust pressure is low. Then once I boot it all the dirt comes out at once through the exhaust. :eek:

Yet the VNT link moves to min flow when I start the car and relaxes again if I shut it off, but what if it's only a small leak that causes vacuum to get lost under load? What do you guys think about that, could it be a likely explanation for the strange sooting behaviour?


Thanks in advance for all replies!

Greetings Marco
 
#21 ·
Cleaning out my EGR and inlet manifold made no different to my soot emissions. I think the 'normal' smoke is soot building up in the exhaust/cats when driving slowly. This is then blown out the back the next time you boot the car.

If I've got this right, I think the VNT moves to 'max boost' position when you start the car which makes sense as you want as much boost as possible under 2000 rpm. When boost reaches a certain point the VNT then moves to throttle the turbo back. Thus, yours sounds good to me. If you were losing vacuum and the car was not getting as much boost as it needs then I would have thought you would trigger an error code?

Keith
 
#22 ·
It also crossed my mind that I should have seen more MCFS messages. However I only had one P1238 until now, but I never saw the MCFS light come on though? As the garage from the previous owner has obviously mounted the drilled plate between the inlet manifold and the EGR I thought I might have come from that and was never properly cleared. I cleared the error a few weeks ago and it never returned until now.

But why do I have such low power below 2000 RPM then? If I reach 2000 RPM it goes off like a rocket and I can clearly feel the boost kicking in. I thought it would be best explainable by a faulty VNT regulation that can't hold the desired position while needing max boost at low revs? :(

Well I'm sure that I'll also take a look at the MAF sensor, allthough it seems unlikely to cause power loss in the lower rev band. Yet I've read about people describing exactly that with a dodgy MAF sensor, though it seems pretty rare... Further I'll also check the MAP sensor if it's clogged and give it a good clean.
 
#23 ·
It does sound odd. If the vanes on the turbo were stuck on 'low boost' position or the VNT was not moving accordingly then you would get poor performance at low rpm. However, I'm pretty sure that would give you an error code.

I'm a bit confused about your EGR though. I thought a blanked EGR would give a continuous error message on the mjet cars? Thus, could yours have been re-mapped to delete the EGR operation? If so, that could cause some confusion here.

If you unplug the MAF and it runs no better then that would eliminate one thing.

Keith
 
#24 ·
Well I have notably poor performance below 2000 RPM! That's what gave me the idea of having something wrong with the VNT. I've read in mutliple places that turbo can work on it's own (max flow/min boost position) from about 2200 RPM, that's also were it really starts picking up in my case.

Regarding the EGR, it is not blanked. All it has is that drilled plate that reduces the amount of exhaust gases that get returned to the intake. According to some research this seems to be a common dirty fix by Alfa Romeo garages for EGR problems...
 
#25 ·
Ah, I understand now. The holes into the intake manifold from my EGR were also very reduced but that was due to soot :)

Might be worth replacing your flexible VNT hoses as a precaution with some new silicone ones. That would be a cheap precaution in case you have an intermittent leak in the feed to the turbo.

Can you read the boost pressure when driving? Fiatecuscan gives a predicted and actual boost pressure that may help to see if you are losing boost due to stuck vanes and/or VNT problem.

Keith

Keith
 
#26 · (Edited)
I blanked my EGR to see if would stop the sooting, which it didnt. But like you say it does cause a constant fault code.

You can test the MAF by unplugging it, and taking it for a drive. This will bring up an error code but will run the car on predicted MAF readings. If it drives much better the MAP is faulty.

Have you tried cleaning your MAP sensor? As someone else mentioned this is what detects if the EGR is working correctly.

As Keith says silicone hose is a good idea, even if you dont hink it causing a problem it will rule it out,

something like this eBay silicone hose 4mm

Not quite sure if its 4mm or 5mm we need, so worth checking first


What you really need is someone local with a working 20v that you can swap sensors with one by one until you come across the culprit!
 
#27 ·
Hello everybody!

Last Friday evening I’ve had a P1235 on harder acceleration. After inspecting the vacuum hoses of the VTG I have found out that they’re pretty porous. Plus the loss of power threshold shifted from below 2000 RPM to more than 2250 RPM. Definitely sounds like an increasingly leaking VTG regulation to me.

I was already able to get the 4mm hose already, but wasn’t able to find any time to exchange them. Did you guys remove the “under-floor panel” to change the one that connects to the solenoid?

I really hope that after exchanging the hoses, that my erratic sooting problem and power loss below 2200 is finally gone…

Best greetings Marco

PS: After changing the VTG hoses I will also try cleaning the MAP sensor as well as temporarily removing the MAF sensor. Never thought that the MAF sensor plug would be so "difficult" to reach though...
 
#28 ·
Hey mates!

I just wanted to provide a quick update as I was finally able to sort out the sooting issue. As I came across many threads with similar issues but not feedback how it was solved in the end, I thought this could also be helpful to others!

One of our last theories was indeed successful: Changed all VGT vacuum hoses and the random smoke screen feature is finally gone as well as the power loss below 2000-2300 RPM.

While inspecting the old hoses after dismounting them, I found out that all of them were more or less leaking somewhere. On the first drive I was almost shocked by the low-end torque it had regained. That’s when I noticed how much I was already missing the feeling of the front tyres struggling for traction on hard acceleration in lower gears…. :D:thumbs:

Thank you again to all that replied!
Marco-Antonio
 
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