Tuning 1.2 conversion runs too lean

[CinqNl]

Hi guys.
I did a 1.2 conversion in my rally cinquecento. I used a uno intake and I polished and ported the head. Now for the mot the exhaust gas test is a fail. The Co and hc are perfect, however the lambda(oxygen in exhaust gas) value is a tiny bit too high. It runs a bit too lean. The exhaust is airtight, so that can't be it. I have driven the car a few hundred kilometer so the ecu has had enough time to adjust, I think. There are errors in the ecu.
Could I be the oxygen sensor in the exhaust? Any thoughts are most welcome.

 

[tomo3292]

Do you run throttle bodies??

Fuel filters?

Fuel pressure regulator??

 

[CinqNl]

No standard throttle body. New filter.
And I have no idea about the fuel pressure regulator. Where can find that? Although I doubt that the problem because the engine runs great and responds perfectly. Except it runs a little too lean.
By the way. I meant to say the ecu has NO errors....

 

[mrcinquecento]

Are you 100% sure the exhaust is airtight right up to the head itself? Can be a small crack or blow in the manifold or manifold gasket.

Normally if it's lean exhaust though it's downstream of the lambda, if it's upstream the lambda will try to correct it with a signal for more fuel.

Have you ran diagnostics such as iaw scan? i'd be interested in what your coolant temp sensor is reading as well as what the ecu is saying the lambda voltages and readings are. Could well just be a dying/clogged lambda sensor.

 

[LeonL]

Which ecu do you run 1.1 or 1.2? Just finished a similar swap today, 1.2 with uno mani. and runs very well not to lean not to rich. runs on a chiped 1.1 ecu

and maybe the cento club holland can help you.

 

[CinqNl]

I used new gaskets for the exhaust, so I am pretty sure it's airtight.
I run the 1.1 ecu because I have read some where on the forum it works with a 1.2. No chip.
I can't run a good diagnostics because my equipment has difficulties connecting to the ecu. I have the cable but lack a proper diagnostic reader.

My initiate suspect is the lambda sensor
However before I simply replace it I wanted some second opinions.

 

[mrcinquecento]

I used new gaskets for the exhaust, so I am pretty sure it's airtight.
I run the 1.1 ecu because I have read some where on the forum it works with a 1.2. No chip.
I can't run a good diagnostics because my equipment has difficulties connecting to the ecu. I have the cable but lack a proper diagnostic reader.

My initiate suspect is the lambda sensor
However before I simply replace it I wanted some second opinions.

Have a look on the guides on here about data logging on the spi. Can be done with a free to download programme (i use iaw scan2 personally) laptop and leads (Vag com cable with ft323 chip and 3 pin fiat/alfa adaptor) from ebay.

This will allow you to get live reads from every sensor including the lambda and coolant temp. show what the iac valve is doing etc etc.

The 1.1 ecu is ok with 1.2 8v btw.

 

[CinqNl]

problem solved.
the lambda sensor works as it's supossed to. I used a snap on ethos to test it, worth the investment. After that to be sure i cleaned the sensor with a special sollution, and refitted the exhaust with some more paste to be sure.
Now the exhaust gas parameters are all in the green.
So there probably was a tiny leak somewhere in the exhaust or although the sensor worked it sended wrong signals because of some foulling, and now it's clean it works fine again.
thanks everyone for the help