General Fiat seicento -question about fuel trims

[Sabbas]

Hello to everyone.I have a fiat seicento sporting mpi 2002.It is second hand with 148000klm.I went to a good friend who has an obd reader just to see the cooling temperature.He take a look and he told me that the fuel trims are very negative and the car try to take fuel away.I have no idea about mechanical (and my english are bad,sorry for that)but i feel that the car has no power.I press the accelerator and feel sluggish.The pedal are stiff.At idling the engine shakes a lot.And i can feel vibration to my steering wheel and to my pedals.When the car is warm sometimes the rev drops a lot but dont shut off.So far i went to three work shops-garage(only for fiat) they put obd scanner to read ecu and they don't find something.No codes.They told me that if a sensor (map,O2 sensors, throttle sensor,etc)had problem must throw a cel.
They change
Spark plugs
Coils
Spark cables
Oil,oil filter,air filter and engine-gearbox mounts
Gear box oil
Temperature sensor
Water pump
Timing belt
Coolant and thermostat
Also they inspect and clean the injections.
After that the symptoms remain the same.My friend put his obd again and told that the fuel trims are negative.Also he mention that when the car cruising and take his foot from pedal the car from close loop goes to open loop.Does anyone knows if that is wright or wrong?Or what is these negative fuel trims?Sorry for all these and for my bad english.Thank you a lot.

 

[Prawny12009]

I would suspect a fuel injection pressure issue if all else has been checked/changed.

Fit a pressure guage to see what your pressure is when running.

Next suspect would be fuel tank purge valve system leaking, if you are pulling fumes from the tank the ECU will try to reduce how much fuel is injected.

You can block the purge pipe temporarily to see if it helps.

 

[Sabbas]

I would suspect a fuel injection pressure issue if all else has been checked/changed.

Fit a pressure guage to see what your pressure is when running.

Next suspect would be fuel tank purge valve system leaking, if you are pulling fumes from the tank the ECU will try to reduce how much fuel is injected.

You can block the purge pipe temporarily to see if it helps.

Good morning Prawny12009.Thanks you for your answer.Two weeks ago i went for fuel injection check.They inspected,cleaned and told me that the pattern flow was ok.I dont know a lot about mechanics.I don't have a pressure gauge to see the pressure of the system.I will go to a workshop to do it and i will inform you.Sorry for the silly question,but these symptoms can be happen from a fuel pump?Purge valve is a small device right of the intake manifold?Above the map sensor? Thanks a lot for your help!!!

 

[Prawny12009]

Is your car single point injection (one injector) or multipoint (4 injectors)

I have little experience on multipoint models, iirc they have no return line so the pressure regulator is in the tank.

 

[Sabbas]

Is your car single point injection (one injector) or multipoint (4 injectors)

I have little experience on multipoint models, iirc they have no return line so the pressure regulator is in the tank.

It is with 4 injectors.So the pressure regulator is set with fuel pump?I will go for a pressure test as you said Prawny12009.The strange is that i have no trouble codes.And the fuel trims are very negative.Ltf at idle is -50 and stf bounce at -20,-10.Thanks for your reply

 

[Prawny12009]

Try blocking off the fuel tank purge line, on single point injection cars there is a carbon filter under the wing with the valve on top (the blue hose iirc) I'm not sure if it is the same on multi point injection.

If the purge system is faulty it will draw fuel vapour directly from the fuel tank.

 

[Sabbas]

It is with 4 injectors.So the pressure regulator is set with fuel pump?I will go for a pressure test as you said Prawny12009.The strange is that i have no trouble codes.And the fuel trims are very negative.Ltf at idle is -50 and stf bounce at -20,-10.Thanks for your reply.

Try blocking off the fuel tank purge line, on single point injection cars there is a carbon filter under the wing with the valve on top (the blue hose iirc) I'm not sure if it is the same on multi point injection.

If the purge system is faulty it will draw fuel vapour directly from the fuel tank.

Prawny12009 thank you a a lot.A silly question,i will block the purge line(i find it,it is a blue hose which goes to purge valve) i must block and the purge valve to or only the blue hose?

 

[Prawny12009]

Prawny12009 thank you a a lot.A silly question,i will block the purge line(i find it,it is a blue hose which goes to purge valve) i must block and the purge valve to or only the blue hose?

For now block the engine side but leave the purge valve side open so that the tank still vents (you may get some fumes under the bonnet)

If you block the purge valve and the hose to the engine you need to fit a vented filler cap

The original cap has a one way vent allowing air in but not allowing any fumes out to atmosphere.

Disconnecting the electrical side of the valve will likely put the management light on.

 

[Sabbas]

For now block the engine side but leave the purge valve side open so that the tank still vents

If you block the purge valve and the hose to the engine you need to fit a vented filler cap

The original cap has a one way vent allowing air in but not allowing any fumes out to atmosphere.

Ok.I will block the engine side and i will inform you about the results.Thanks a lot for your time and your help Prawny12009

 

[Sabbas]

Ok.I will block the engine side and i will inform you about the results.Thanks a lot for your time and your help Prawny12009

Good morning Prawny12009.I block the engine side but i have the same issues.Also i haven't improvement in my obd readings.They are the same.At hot idle i have these readings:

Do you see anything strange at these readings?Thank you for your time