2006 fiat stilo 1.6
Bought car without CAT.

I have spoke about my beast in a previous thread but since I replaced a few things i decided to make a new one.

Symptoms:
Rough idle at times until I switch it off then start again and will idle better with a slight drop in rpm

Hesitating acceleration most of the time,almost always.especially at lower rpm its more prominent. Once you hit 5th gear she seems to be better. At times though she accelerates no problem,no hesitation and other times she accelerates with hesitation right through the rpm range but mainly between pull away and 2500rpm

Ralf S on this forum explained another drive test where you accelerate slowly and steady throttle from around 1000rpm in 2nd and see what happens at 1800rpm. At 1800 rpm she hesitates therefore failing the test.
Kept at 1800rpm while driving she jerks continuously until you go give more throttle.
If you let off throttle completely while driving around 1800rpm she doesn't decellerate smoothly but harshly.

If you try to pull her flat foot right until red line,she won't go until the red line. She stops just under 5000rpm and stays there.

Poor fuel economy,normal slow driving in city and hardly stopping,she averages 8 to 9 l/100km.which for her is bad.

Diagnostics:
CEL is on and I get a p0141 code and no other. I read post CAT does not affect fuel trim(causing hesitation and slow acceleration etc)downstream o2 sensor readings shows no voltage AT ALL.I have a spacer on there too(previous owner must have put it on when removing CAT)

Upstream sensor has no code,I captured data and saw the sensor jumps around between 0.2 to 0.8. Not very erratic.
STFT jumps around pretty erratically though. It goes from -60 to 18 back to negative. She doesn't go much into positive but stays mostly in negative and at times she hits -100. That to me is very erratic. The O2 upstream sensor does not respond erratically like the STFT. That indicates to me its a lazy sensor which isnt setting a code. Am I right?

I have replaced :
Fuel pump
Spark plugs
Oil filter
Coil packs are all firing
* I had a k&n cone filter on and swopped it back to original box and replaced the panel filter in it with a brand new one
Timing belt and tensioner
Cleaned throttle body and crank ventilation(white liquid slime in crank ventilation) car doesn't use coolant,stays on max and no coolant in oil and no overheating(signs of blown gasket)

After replacing air filter I took her for a drive and same symptoms.

So what next can i look at? Is it the o2 sensor because all signs point to it? What else can I check?

I am going to replace the o2 sensors though. Besides o2 sensor where else can I check ?
And is the o2 sensor on 1.6 a wideband sensor?

These pics are during idle!

Thanks for the help

Do you have MES or any other scanner? maybe you could do datalog while riding with the car?

flyingdutch said:

Do you have MES or any other scanner? maybe you could do datalog while riding with the car?

Click to expand...

Thanks for the reply.

I have checked data while driving.

In my diagnostics paragraph those erratic fuel trims i mentioned and mostly negative stft was taken during driving.

I just posted those pics. I will post a link to a video of the data logging during driving...

flyingdutch said:

Do you have MES or any other scanner? maybe you could do datalog while riding with the car?

Click to expand...

Here is link to video during driving of upstream o2 voltage and STFT.

Downstream which has a code has no voltage AT all. However I herd downstream shouldn't affect fuel trim etc

https://youtu.be/agxCQDuSE30

You mentioned that downstream sensor has a spacer on it? What sort of spacer is that?

I don't know what the values mean or what values would be normal, but doing it "analogue", by the car's symptoms, it looks like the lambda sensor is knackered, so unless you change that, anything else could be just a symptom of the same problem.

The rear lambda giving no signal sounds a bit problematic too. I'm guessing FIAT didn't fit it just because they had a batch of them lying around, so it must do *something* for the fuel trim. You ought to resolve that issue too.

Is the spacer a very obvious "added" component, e.g. a big washer that has been added to the lambda? It could be the lambda sensor is the wrong one and the previous owner tried to adjust its depth into the exhaust pipe by packing it out with any washer he could find to fit.

Or is the spacer a round collar that is welded to the exhaust pipe? If it's a welded on collar, it would be original spec. My Alfa 145 and 155 both had a collar. I think the factory uses this arrangement to space the lambda correctly.

Ralf S.

Hi everyone,

So yes it looks like a obvious added part.
It looks similar to one in the pic.

So I have read that post CAT measures CAT efficiency and how much oxygen is present after the CAT then fine tuning the AFR.

That sounds correct.

What I can do is try and remove the spacer and fit it normally and see what happens?
One day I got a slight slight reading. Like I saw the graph go up very very little but enough to see a smooth increase in voltage then like it switched off again.

Are the stilos o2 sensor wideband or narrow band?

Pics of spacer example

I guess it's just a sniffer mode for 2nd O2 sensor to trick it to thinking that the car still has a working cat so if you'll remove it it should throw a p0420 code

flyingdutch said:

I guess it's just a sniffer mode for 2nd O2 sensor to trick it to thinking that the car still has a working cat so if you'll remove it it should throw a p0420 code

Click to expand...

I am going to keep the spacer on because the car did drive excellent when we bought it. It's not as if it was driving like this always.

But I am going to replace upstream o2 first then downstream. (Finances allow me to buy one at a time)

I've herd mix info about downstream sensors,do they actually affect performance?

Yes they do actually affect performance, and about that extention fitting make sure its not clogged or damaged in some ways. I have seen some of them contain small portion of cat in it to trick the sensor while others just move the sensor away from airflow, however if your sensor displays 0v signal it means that ecu knows that mixture after the cat is terribly off so it engages lower power mode through trying to correct it. That's most likely an answer to your stft going to - 70 when basically it should stay stable - 12to +12 on stable throttle input. Could you take a photo of you motor and its surroundings with the hood open?

flyingdutch said:

Yes they do actually affect performance, and about that extention fitting make sure its not clogged or damaged in some ways. I have seen some of them contain small portion of cat in it to trick the sensor while others just move the sensor away from airflow, however if your sensor displays 0v signal it means that ecu knows that mixture after the cat is terribly off so it engages lower power mode through trying to correct it. That's most likely an answer to your stft going to - 70 when basically it should stay stable - 12to +12 on stable throttle input. Could you take a photo of you motor and its surroundings with the hood open?

Click to expand...

When I inspect my sensors,they covered in soot. I already removed the extension and cleaned it out and no change.

As a precaution that won't cost much,I'm going to clean intake manifold. I cleaned the throttle body already.

Any tips and hints on removing the manifold and is it recommended?
I hear that carbon deposits can form in the manifold blocking airflow causing a some sort of hesitation in acceleration.

Yes I will take a photo of my engine bay for you and post it. Just resting my hand as I injured it yesterday.

Thanks for the help

Ralf S. said:

I don't know what the values mean or what values would be normal, but doing it "analogue", by the car's symptoms, it looks like the lambda sensor is knackered, so unless you change that, anything else could be just a symptom of the same problem.

The rear lambda giving no signal sounds a bit problematic too. I'm guessing FIAT didn't fit it just because they had a batch of them lying around, so it must do *something* for the fuel trim. You ought to resolve that issue too.

Is the spacer a very obvious "added" component, e.g. a big washer that has been added to the lambda? It could be the lambda sensor is the wrong one and the previous owner tried to adjust its depth into the exhaust pipe by packing it out with any washer he could find to fit.

Or is the spacer a round collar that is welded to the exhaust pipe? If it's a welded on collar, it would be original spec. My Alfa 145 and 155 both had a collar. I think the factory uses this arrangement to space the lambda correctly.

Ralf S.

Click to expand...

Hi Ralf.

So we have an income now so sorting the beast out first on the list?

I wanted to mention though that when she has that hesitation on acceleration,she kicks out a clear-ish thin smoke then clear.
When in traffic yesterday,when I pulled away from traffic light after sitting in the traffic,she also kicked out that clear-ish smoke then cleared up.smoke didn't have a black colour pointing to over fueling.

The beast would idle rough when sitting in traffic long but as soon as you open her she idles better at the next traffic light.as if she only wants to drive fast. I don't always drive her fast but I do stretch her legs now and then

NebulaStilo said:

Hi Ralf.

So we have an income now so sorting the beast out first on the list?

I wanted to mention though that when she has that hesitation on acceleration,she kicks out a clear-ish thin smoke then clear.
When in traffic yesterday,when I pulled away from traffic light after sitting in the traffic,she also kicked out that clear-ish smoke then cleared up.smoke didn't have a black colour pointing to over fueling.

The beast would idle rough when sitting in traffic long but as soon as you open her she idles better at the next traffic light.as if she only wants to drive fast. I don't always drive her fast but I do stretch her legs now and then

Click to expand...

The thin smoke could be unburnt fuel vapour. It's generally described as "blue" but if there's any oil in the exhaust it always looks black to me...

Anyhow, it seems too much of a coincidence that we think your car is over-fueling and then there's something that could be fuel vapour/rich in the exhaust gas.

Rough idle could be the car/idle controller trying to stop the engine racing because of a too-rich mixture. It would clear up once you're moving, since when the lights change you're going to give it a big throttle opening, so a lot more air can get in.

So.. it all still could be that the mixture is incorrect because of what we think is the lambda sensor(s) being duff.

I hope new lambda sensors will fix it (it's good that you have some cash again.. ), just to satisfy my curiosity. Sometimes all the signs point to one thing and then it turns out there's a dead mouse in the inlet manifold or something completely random..


Ralf S.

Ralf S. said:

The thin smoke could be unburnt fuel vapour. It's generally described as "blue" but if there's any oil in the exhaust it always looks black to me...

Anyhow, it seems too much of a coincidence that we think your car is over-fueling and then there's something that could be fuel vapour/rich in the exhaust gas.

Rough idle could be the car/idle controller trying to stop the engine racing because of a too-rich mixture. It would clear up once you're moving, since when the lights change you're going to give it a big throttle opening, so a lot more air can get in.

So.. it all still could be that the mixture is incorrect because of what we think is the lambda sensor(s) being duff.

I hope new lambda sensors will fix it (it's good that you have some cash again.. ), just to satisfy my curiosity. Sometimes all the signs point to one thing and then it turns out there's a dead mouse in the inlet manifold or something completely random..


Ralf S.

Click to expand...

Hi Ralf.

Thanks for the reply.

Yes she does have a strong fuel smell especially in traffic and as the car starts after standing overnight.

I'm first going to change battery this month because she's taking long to start and has a weak turn over when trying to start.

Sometimes she will have a good start but just turns over but doesn't start.as if she's starved of fuel. Then I must switch ignition off and on and then on 2nd or third try she will start.

The other night so the beast caught a 1.4 toyota RunX's(thats what its called in South Africa)eye.
So at the traffic light I decide to give the beast a go at this toyota and on pull away she couldn't even sit with the Toyota. I was embarrased???
Luckily there were a few cars ahead so he slowed down and the beast caught up and had momentum so then she kept next to her but was hesitating and couldn't keep next to him long and lost the drag race???

Its sad when you know the true acceleration of the beast and even if she not hesitating,she's sluggish also.

Thanks for the info and the concern
?

Ralf S. said:

The thin smoke could be unburnt fuel vapour. It's generally described as "blue" but if there's any oil in the exhaust it always looks black to me...

Anyhow, it seems too much of a coincidence that we think your car is over-fueling and then there's something that could be fuel vapour/rich in the exhaust gas.

Rough idle could be the car/idle controller trying to stop the engine racing because of a too-rich mixture. It would clear up once you're moving, since when the lights change you're going to give it a big throttle opening, so a lot more air can get in.

So.. it all still could be that the mixture is incorrect because of what we think is the lambda sensor(s) being duff.

I hope new lambda sensors will fix it (it's good that you have some cash again.. ), just to satisfy my curiosity. Sometimes all the signs point to one thing and then it turns out there's a dead mouse in the inlet manifold or something completely random..


Ralf S.

Click to expand...

Hi Ralf
So I ordered new sensor. Today I took it for a drive with sensor unplugged just to see how she will drive.

The car didn't surge or hesitate upon acceleration. She ran rich. Got a P0172 code and O2 sensor circuit b1s1.

That definately points to o2 sensor right ?

She's still bit sluggish but pulls much better AND she doesn't have that surge.

A new sensor and Good PCV clean what you think?

And any tips on cleaning the PCV?

Thanks