Technical GP 2009 Petrol / LPG 1.2 8V - Understanding Lambda Readings

[francocm]

Hi guys,

I have some issues relating to performance, and the LPG service garage noticed a constant juggling between lean and rich mixture and advised me to have it checked out.

The car is a 2009 Grande Punto 1.2 8V Petrol converted to LPG.

So now I did the following:

1) Connected MultiEcuScan.
2) Plotted a graph of:
--- Lambda 1 signal (Pre-Cat.)
--- Lambda 1 signal (After-Cat.)
--- Lambda sensor 1 integrator
--- Lambda sensor 2 integrator
--- Lambda 1 diagnosis (Pre-Cat.) (this is not plottable)
3) Did a 'self-adaptation parameters' reset and a 'phone wheel learn' reset.
4) Plotted the same graph as point 2 above.

I noticed that the 'Lambda 1 diagnosis (Pre-Cat.)' reading constantly switches between lean and rich every ~1.5 seconds which is not good from what I can understand.

Some background information: The car was converted to LPG after-market. Recently I noticed that the LPG injectors going into the intake manifold are connected a bit wonky and they're held in place only with some metal glue. Could it be that excess air is going inside the intake manifold due to this, and the car ECU is caught in an infinite loop trying to correct this?

You can find the screenshots attached.

If anyone can help in understanding these lambda graphs please, I would be grateful.

Thanks

Edit: Forgot to mention, the readings are taken on Petrol not LPG.

 

[portland_bill]

Not looked at lambda graphs before, so no idea if that is normal or not.

The lambda sensor will rapidly switch between rich and lean, as the ECU adjusts the fuelling, so this could well be a normal reading. If there was an air leak, I would expect it to run weak, with a constant correction towards richer, giving a flatter graph, either higher or lower. Just theorising at this stage.

To test if the injectors are allowing air in, test this by spraying WD40, or similar at them with the engine running. If there is a leak, it will suck in the spray and the engine note will change.

It might help if you described the problem you are experiencing, as your original post does not tell us this.

 

[francocm]

Thanks for the reply. What you say makes sense too.

Regarding my problem:

Basically lately I've lost a noticeable amount of power. To put you in the picture, there is this particular hill which the car used to be able to handle at 110-115km/hr quite easily. Now it's only managing at 85-95km/hr, rarely touching 100km/hr. Always with the same load in the car (I.e. just me).

I can notice the loss of power at any point in driving wherever I need power, ex. Moving from 0 at an uphill road; or I need to accelerate quickly.

Issue is there regardless of whether I'm on Petrol or LPG.

Driving with 5 people on board (including driver) becomes a bit difficult....

Worth mentioning but not sure whether it's relevant, a few months ago I had an exhaust leak due to some studs on the exhaust manifold being broken and the air leaking from there. This was fixed around 2 months ago. I noticed a bit of an improvement after this, but nothing spectacular.

 

[cmosfxx]

That's how lambda sensor works.

Switching voltage on pre-cat sensor indicates a good sensor. (Well not always but anyway). A lambda sensor will generate up to about 0.9v when the fuel mixture is rich and about 0.1v when the mixture is lean. And because that's how the engine works you see this switching voltage result on your graph.

Post cat sensor should maintain a constant voltage on idle. If the voltage follows pre cat then you have a bad cat.

(Notice that all these applies only at idle-closed loop)

Now about your graphs.

Like I said the switching voltage is a good thing but you expect a voltage between 0.1 and 0.9v.

Since you have a max voltage of 0.73v you have a lean mixture.

This could be from a leaking injector like you suspected.

Can you post adaptation bank 1 MUL and ADD?

 

[francocm]

Thanks for the reply.

Can you explain what "post adaptation bank 1 MUL and ADD" are? Extra parameters in MultiEcuScan?

I'll give it a look later today. Noticed also that consumption isn't that impressive either. Since the reset 3 days ago, I'm averaging 11.1km/l where it used to be around 12.5 - 13. Always on Petrol. Even before the reset I had the same consumption.

Thanks

 

[cmosfxx]

Yes you can find them in multiecuscan.

 

[Andy Monty]

Check the map sensor is working correctly

 

[francocm]

So... I couldn't find anything about 'post adaptation bank 1 MUL and ADD' in MultiEcuScan... is that how they are called?

In the meantime, I re-did the test since I've been driving approx 3 days since the reset. You can see it attached.

I also went for a ride, and recorded a bunch of parameters which you can see in the CSV: https://www.dropbox.com/s/rjmihm3bsli0s4i/drivetest2.csv?dl=0

What surprises me:
- The amount of times engine torque is 0Nm when the desired is quite a different value. Why 0?
- The amount of times that idle air correction goes up to 6553.5%. This is funny because the maximum value of an unsigned short (16-bit number) is 65535. To me this means that the sensor / reading is at its maximum possible.
- Lambda 1 Status (after cat.) is almost all the time in 'open-loop'.
- Lambda 1 Diagnosis (after cat.) is initially 'Not Active', but eventually starts doing the rich / lean cycle too just like the pre-cat. Is this fine?

Now, I am a software developer, not a car expert, so I have absolutely no idea what the above means in terms of cars, but I'm trying to apply some logic to the problem to the best I can with what I know. Please correct me where I don't know or get wrong.

Also, strangely enough, the car feels happier if I drive with the a/c on... it's like the a/c is cushioning / compensating for something due to its load... Shouldn't it be the opposite? This doesn't happen always.

Thanks for the feedback.

 

[francocm]

Check the map sensor is working correctly

How do you do this please?

Thanks

 

[Komuta35]

Bro, I need to reach you. I have the same issue. How did you fix it?

 

[Komuta35]

So... I couldn't find anything about 'post adaptation bank 1 MUL and ADD' in MultiEcuScan... is that how they are called?

In the meantime, I re-did the test since I've been driving approx 3 days since the reset. You can see it attached.

I also went for a ride, and recorded a bunch of parameters which you can see in the CSV: https://www.dropbox.com/s/rjmihm3bsli0s4i/drivetest2.csv?dl=0

What surprises me:
- The amount of times engine torque is 0Nm when the desired is quite a different value. Why 0?
- The amount of times that idle air correction goes up to 6553.5%. This is funny because the maximum value of an unsigned short (16-bit number) is 65535. To me this means that the sensor / reading is at its maximum possible.
- Lambda 1 Status (after cat.) is almost all the time in 'open-loop'.
- Lambda 1 Diagnosis (after cat.) is initially 'Not Active', but eventually starts doing the rich / lean cycle too just like the pre-cat. Is this fine?

Now, I am a software developer, not a car expert, so I have absolutely no idea what the above means in terms of cars, but I'm trying to apply some logic to the problem to the best I can with what I know. Please correct me where I don't know or get wrong.

Also, strangely enough, the car feels happier if I drive with the a/c on... it's like the a/c is cushioning / compensating for something due to its load... Shouldn't it be the opposite? This doesn't happen always.

Thanks for the feedback.

How did you solve the problem? I absolutely need to learn, my friend.

 

[GrandePunto PL]

Just learn basics in the Internet. There is enough content already.
YouTube is full of examples of how lambdas work, how to diagnose (real diagnosis: oscilloscope + exhaust gas analyzer).
Not so much on LPG, but still you will find something if you really care and put man-hours into it.

What's your problem, specifically? Evidence, hard data, OBD2 logs (or at least screenshots from FES or MES). What's "wrong"?
Do you maintain your car well? Really? Any preventive maintenance (or just waiting for Check_Engine light)?
Is the LPG installed correctly? What's the engine? Is it 8V? Ever heard of "valve clearance"? It goes bad on LPG when left unchecked for years.
Do you have obligatory inspections each year in your country? Do they check emissions? Do you care what the results say (or just if it's Pass/Fail)?
To diagnose engine/exhaust you need external validation. Otherwise you cannot trust your oxygen sensors to "diagnose" a car.

 

[Komuta35]

I am a technical person myself and understand technical matters. I have been investigating this issue for a month, and such a fault does not exist. Right now, only this colleague has encountered the same issue. The valve adjustment, etc., has all been done. I have researched everything, including YouTube and AI. Today, the materials were checked. There is nothing I haven’t investigated. Here is the exact issue as described by the colleague. Now, tell me the solution.

Just learn basics in the Internet. There is enough content already.
YouTube is full of examples of how lambdas work, how to diagnose (real diagnosis: oscilloscope + exhaust gas analyzer).
Not so much on LPG, but still you will find something if you really care and put man-hours into it.

What's your problem, specifically? Evidence, hard data, OBD2 logs (or at least screenshots from FES or MES). What's "wrong"?
Do you maintain your car well? Really? Any preventive maintenance (or just waiting for Check_Engine light)?
Is the LPG installed correctly? What's the engine? Is it 8V? Ever heard of "valve clearance"? It goes bad on LPG when left unchecked for years.
Do you have obligatory inspections each year in your country? Do they check emissions? Do you care what the results say (or just if it's Pass/Fail)?
To diagnose engine/exhaust you need external validation. Otherwise you cannot trust your oxygen sensors to "diagnose" a car.

 

[GrandePunto PL]

Don't lie. You have not "searched" much (topic is covered extremely well, in English). And you are not so "technical" at all my friend.

First, answer my questions. In case you haven't noticed, there are already tips in there (they are questions + advice, 2 in 1).

Original poster said, his LPG was installed incorrectly or careless, possibly leaky intake (LPG injectors area).
Take an exhaust test. And come back here with print, results. Then we can talk...
You are not in position to demand solutions like that, "tell me", "give me" (no one knows exact solution when problem is not clear).

Posted lambda waveforms were not perfect, but acceptable (his car should drive OK). Not enough data to spit a "solution".
Car can NOT "diagnose itself" (to some extent only), that's why you need exhaust gas analysis.

Your car is probably neglected, has some basic problems, lack of basic maintenance (old oil and spoiled VVT if it's 1,4 8V, old timing belt, leaky exhaust, bad old sensor or two or more, low fuel pressure, incompetent LPG shop modified the car and so on).

 

[Komuta35]

Yalan söyleme. Çok fazla "arama" yapmadın (konu İngilizce olarak çok iyi ele alınmış). Ve sen hiç de "teknik" değilsin dostum.
Önce sorularıma cevap ver. Fark etmemiş olabilirsin, orada zaten ipuçları var (sorular + tavsiyeler, 2'si 1 arada).
Orijinal posterde LPG'sinin yanlış veya dikkatsizce takıldığı, muhtemelen emme kısmında (LPG enjektörleri bölgesinde) kaçak olduğu yazıyordu.
Bir egzoz testi yapın. Ve sonuçları yazdırarak buraya geri gelin. Sonra konuşabiliriz...
Siz bu şekilde çözüm talep edecek durumda değilsiniz, "söyle", "ver" (sorun anlaşılmadığında kesin çözüm de bilinmez).
Gönderilen lambda dalga formları mükemmel değildi, ancak kabul edilebilirdi (arabası sorunsuz gitmeli). Bir "çözüm" üretmek için yeterli veri yok.
Arabanız muhtemelen bakımsızdır, bazı temel sorunları vardır, temel bakımları yapılmamıştır (1,4 8V ise eski yağ ve bozulmuş VVT, eski triger kayışı, sızdıran egzoz, bozuk eski sensör veya iki veya daha fazla sensör, düşük yakıt basıncı, beceriksiz bir LPG atölyesinin arabayı modifiye etmesi vb.).

I think you have trouble understanding what you read. The guy said he fixed them in place because there might be a leak, but the error didn’t go away. He clearly mentioned in the post that the same issue persists. You’re struggling to comprehend what you’re reading. I’m not asking you the question; I’m asking if there’s a way to reach the person who posted this. Please don’t reply to me.

 

[GrandePunto PL]

First, learn how a forum works and how people behave (mostly, demand solutions). Original poster started this thread 10 years ago.
Most (99%) people will disappear and not finish/close the threads (no solution). Good luck reaching the guy after 10 years...
You can't stop me. You can't also fix the easiest car on the planet, with old FIRE family engine. Due to lack of basics, dear "technical person".
That's OK if you want to learn. But you clearly DON'T. You just demand solution, NOW.
But this is not how the Internet works...

You can Ignore me, there is such option somewhere on the forum. Now, THAT's a Solution.

 

[jackwhoo]

How did you solve the problem? I absolutely need to learn, my friend.

Hi,
You have not explained what problem you are having.
The original poster hasn't posted on forum for a long time.
J

 

[Komuta35]

Hi,
You have not explained what problem you are having.
The original poster hasn't posted on forum for a long time.
J

My issue is exactly the same as what the other guy described. It seems like no one else has experienced this problem. I can't find any discussion about it anywhere. I’m just hoping that the original poster might reply.

 

[Komuta35]

Vehicle Information:

• Model: 2008 Grande Punto 1.4 8V - 120,000 KM
• Fuel System: Petrol + LPG

When I connect the car to Multiecuscan, I get the following readings:

• Lambda 1 Diagnosis (Pre-Catalyst): Constantly switching between lean and rich (~1.5 seconds).
• Lambda 1 Status (Post-Catalyst): Always in "Open Loop" mode.
• Lambda 1 Diagnosis (Post-Catalyst): Initially "Not Active," but over time, it starts fluctuating between lean and rich.
• Idle Air Correction: Reaches up to 6553.5%.

Because of this, the trip computer shows incorrect fuel consumption values, and the car's performance is very poor.


Lambda sensors are fine.
Sensors are not the issue.
MAP sensor is fine.
Valve adjustment was recently done.


There seems to be no solution to this problem.

 

[jackwhoo]

Upstream o2 sensor should switch high low - so appears correct

Post cat o2 sensor can be ignored as doesn't affect fuel or performance. Plus you don't have code for cat poor performance.