Technical Fiat Puno Mk2 - huge fuel consumption!

[puntoFix]

Basically means car fuel mix is being controlled by the reading from the first lambda sensor.
It uses the reading to control the mix of air and fuel.

When you cold start it is in open loop as the lambda needs to be hot, engine up to temp etc.

So the engine is forced to be rich ie have more fuel than air, hense exhaust stinks and revs are higher at start. A bit like pulling the choke out on older cars on start up, when everything is up to temp you push choke back in.

When in closed loop the ecu alternates the mixture from rich to lean so the Cat converter can work on the different gas produced.

https://secure.lambdapower.co.uk/TechNotes/Tech-3.asp

So yep sounds like your thermostat is working it will be shut ( no flow of hot water in to radiator) until up to working temp then open to keep engine at working temp.

Also sounds like your going into closed loop if the revs drop below 1000 after a bit.

disconnecting battery will clear codes.

 

[lesavage]

Thanks alot @putnoFix! You taught me how to check if thermostat is working properly!

I found what was causing my issues guys, a guy named Ziggy122 explained the case here: https://www.fiatforum.com/punto-ii/331816-mk2-punto-coolant-temperature-sensor.html?p=3302068

So as he says when ECU can't read temperature from the sensor it does this:

A - Put the EML light on
B - The temperature guage may go off / red light come on but register cold
C - Overfuel, overfueling gives a cooler combustion = Less heat produced
D - The Radiator fan switches on
E - The car may reduce availible power, to help prevent excessive heat build up

And I guess thats what happened to my Punto, I had loose connection or dying temperature sensor, so ECU did what it had to and it was left like that. So I had that C (overfuel) turned so engine produces less heat. And thats exactly what happend to me, EML light on, temperature gauge went to zero, radiator fan switched to 100%, and obviously fuel consumption was huge!

When I cleaned contacts and removed battery, I reseted the ECU without even knowing it, and it cleared codes and everything got back to normal so my fuel consumption was normal again.

Now I just need to get code reader and see how is my coolant temperature doing and check if thermostat is working as it shoud, puntoFix explained that perfectly! And will change temperature sensor as that sensor triggered this issue for me. Heck, I might even change whole radiator, this car deserves it.

I hit a deer once, radiator was all bent, but didn't leak coolant. It was so bent that fan would not spin as radiator was in the way. I used two long pieces of wood to straighten the radiator so fan can spin again and thats it, this little champ made another 80 000 km like that. I'm telling you this car, Punto MK2/B is unbeatable! The amount of abuse he endured with me is just ridiculous. I bought it cheap, and was like... will drive it till I break it, damn thing just won't break. Now I decided to truly make this car as new, will little by little upgrade all parts and make it as good as new.