OBDII : LONGFT1 -15% at idle ( Car running rich )

[biomecanoid]

Hello,


I just checked yesterday my car ( Daihatsu Sirion 2006 1000cc ) with the OBDII tool and found the Long term fuel trim to be -15% when parked idling ( Tested after driving ).

I do remember both short and long term fuel trim being at exactly 0% a few days ago.

I don't believe this is normal, Anything I can do ?

On 23/05/2021 both short and long fuel trim were at 0%.

Air filter is clean, ( also run the car without the filter ) and on 10/05/2021 I added to the fuel STP Fuel System Cleaner.

I thought since the car is 15 years old and still with the original fuel pump it must be dirty.

I don't know if its relevant but I also have a CAT_RDY INC.

Car is running fine no errors codes or check engine light and I have already gone thru the tank with STP



Thank you

Chris

 

[LazyDog]

How about checking the purge valve if open you can get some fumes causing the rich condition

 

[biomecanoid]

Thanks for you reply, I have posted my issue on other forums as well, your are the 1st to give a straight forward answer for something tangible and not vague.

 

[biomecanoid]

I will be posting more info

 

[biomecanoid]

Arriving home after 30min drive and idling 10min:

 

[biomecanoid]

Arriving home after 30min drive and idling 20min:

 

[biomecanoid]

Leaving car to cool off for 40 and then idling for 15min:

Revving the engine leaves black smudge on the ground, no visible smoke whatsoever

 

[doublebase]

It’s running rich, so a few possibilities....bad fuel pressure regulator, leaking injector. Mass air flow sensor could give false readings and send the computer to lean up. But you’re actually getting soot coming out of the tailpipe, so you are dumping too much fuel.

 

[LazyDog]

Besides the above your car has a MAP sensor, try cleaning it out and see if the readings change.

Your MAP readings, I am not sure if they are correct.

Check the readings for the O2 sesnors and let us know if you have a short or wide band for the up stream O2.

 

[biomecanoid]

Besides the above your car has a MAP sensor, try cleaning it out and see if the readings change.

Your MAP readings, I am not sure if they are correct.

Check the readings for the O2 sesnors and let us know if you have a short or wide band for the up stream O2.

The O2 Sensors are marked as O2S11 and O2S12 on the above pictures

 

[biomecanoid]

It’s running rich, so a few possibilities....bad fuel pressure regulator, leaking injector. Mass air flow sensor could give false readings and send the computer to lean up. But you’re actually getting soot coming out of the tailpipe, so you are dumping too much fuel.

Could it also be a bad catalytic converter since I am getting CAR_RDY INC ?. Could a bad catalytic converter he causing all the ill effects I am experiencing ?

 

[biomecanoid]

Also if you look at the above pictures the O2S12 is at 0.080v which seems too low in regards to the O2S11 sensor. Could the sensor be bad ?

 

[mattd]

if that downstream sensor is correct it’s reporting an extremely lean condition which clearly isn’t the case. Does this engine have a vacuum style fuel pressure regulator? If so check that for rupture, also check the purge solenoid for evap on engine for leaking by.

 

[doublebase]

if that downstream sensor is correct it’s reporting an extremely lean condition which clearly isn’t the case. Does this engine have a vacuum style fuel pressure regulator? If so check that for rupture, also check the purge solenoid for evap on engine for leaking by.

I forgot about the purge solenoid, good call.

 

[doublebase]

Could it also be a bad catalytic converter since I am getting CAR_RDY INC ?. Could a bad catalytic converter he causing all the ill effects I am experiencing ?

No, the converter is not going to cause fuel trim issues.

 

[biomecanoid]

So since the car is running rich and dumping raw fuel on the catalyst that triggered the CAT_RDY INC correct ?

Also if the Catalyst is bad and all the crud is accumulating onto the oxygen sensor and its not working properly would that cause fuel trim issues ?

 

[LazyDog]

So since the car is running rich and dumping raw fuel on the catalyst that triggered the CAT_RDY INC correct ?

Also if the Catalyst is bad and all the crud is accumulating onto the oxygen sensor and its not working properly would that cause fuel trim issues ?

Cat-RDY inconclusive it probably means that the cycles are not complete. Every car has a drive cycle before the monitors go into ready statues.

The O2 readings for the front sensor are correct but the rear O2 is very lean. How old is this sensor if original they tent to go lean when they are bad.

 

[biomecanoid]

Cat-RDY inconclusive it probably means that the cycles are not complete. Every car has a drive cycle before the monitors go into ready statues.

The O2 readings for the front sensor are correct but the rear O2 is very lean. How old is this sensor if original they tent to go lean when they are bad.

The car is a 2006 Daihatsu Sirion 1000cc I would assume that its the original sensor. I have the car since 2018

 

[biomecanoid]

Would cat cleaner help the situation ?

 

[LazyDog]

Would cat cleaner help the situation ?

I have never used cat cleaners, not sure!