Hello,
I have a alfa romeo mito 1.4 t-jet (120PS) with A LONG TERM FUEL TRIM of -22.
Sometimes it gets to -25 and throws a P1172 code.
o2s1 is around 0.8V and o2s2 is around 0.4V at idle. I changed the o2s2 sensor and nothing happend.
Intake manifold pressure: 34 kpa.
P.S. I know it is a fiat site but they have a lot in common

Are you monitoring the figures with mes while the engine is under load or while the engine is idling?

What are you using to read the LTFT?
A LTFT of -22 would mean there's to much fuel.
The O2 sensor might be reading correctly... so stuck at full rich 0.8v..

How and in what conditions did you measure the O2 sensors?
How.. and in what conditions did you measure the intake pressure?
Was the engine fully up to temperature? and started for a least 5 minutes? (i'm asking because there are some minimal time and temperature thresholds before the O2 actually read...before that you just read a voltage set by the ECU)


Check fuel pressure...you need to actually check it
You can make your own fuel pressure tester for under 10euro : you'll need a T (tee) connector, a few cm of 8mm (internal diameter) fuel hose, and a 0-6 bar pressure gauge...can get a cheap one from LeroyMerlin for 10-15 lei (...).

I am using a ELM327 with torgue/car scanner apps.
I got these values at idle.

Then 34kpa is a positive value in psi, and a petrol engine should be a negative value at idle (a vacuum). Check for a vacuum leak in the breather system

Update:at idle
The o2s1 goes between 0.1 and 0.8 V
The o2s2 between 0.5 and 0.7

Craig830 said:

Then 34kpa is a positive value in psi, and a petrol engine should be a negative value at idle (a vacuum). Check for a vacuum leak in the breather system

Click to expand...

Craig830 34kpa=340mbar...since atmospheric pressure is ~1000mbar .... the intake pressure is lower than atmospheric..so what you could call vacuum.

ianis said:

Update:at idle
The o2s1 goes between 0.1 and 0.8 V
The o2s2 between 0.5 and 0.7View attachment 195620View attachment 195621View attachment 195622

Click to expand...

So the O2 sensors are reacting as they should.


So why the problems with the FT?
Do you have any modifications on the car?

The engine is a t-jet 120ps but the ecu has the 155ps map(that's how i bought it). I haven't done any other modifications.
Should i try to clean the 2 map sensors?
Will it help if i buy a KKL-line with multiecuscan?
The P1172 code appears once a month.
The engine feels underpowered for some time(2-3 days), then "check engine light" appears(long term goes to -25%) and the engine power/response gets better.

Somebody was playing around with it .

For now do as i said check fuel pressure. then read the codes off each injector... you need to make sure they are the right ones.

The different map might be a problem (the 1500 has different cams in it so it consumes more air).... but i don't think it's going to be worth 25%.

I bought a vl36 turbo from a t-jet 150ps so i'l be changing that.
What's the normal fuel pressure?

I'd not replace the turbo yet, you don't want to add more unknowns (Is the turbo good, was it properly installed, etc etc)
The vl36 turbo won't solve the fuel trim issue.
It will just give you more air in the top of the rev range.


Fuel pressure varies based on intake pressure/vacuum
~3.5 bar with engine off (while the pump is priming)
~3.2 bar with engine off + pump off
~3 bar with engine on, at idle
~4-4.5 bar at full throttle on the road .. or a dyno. (you won't see this while standing still)

I'm telling you to check the fuel pressure.. because bad/clogged fuel pressure regulator will create more fuel pressure.. causing the FT to drop trying to compensate.

Im telling you to check the injectors because they might have had a totally different turbo and tune on it before... for example the TD04 turbos require different injectors... and those WILL cause the FT error on a normal/stock tune.

I cleaned the MAP sensor near the injectors which was dirty and wet with gasoline.
Fuel pressure and fuel pressure regulator are good.
(Photo of the injector ramp)

You didn't measure the pressure. how do you know it's good?
Don't care about the injector rail... you need to remove it... and check each injector... each one has a few code on them.

I'm going to stop trying to help. Good luck!

Thanks for your help.