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

[circuitsmith]

FIrst, if the front O2 sensor is working properly the car is not running rich.
The O2 sensor has the final say and will bring the mixture to hover around stoichiometric when in closed loop.
The computer is compensating for the difference between what the fuel map expects and what the O2 sensor indicates.
As long as the trim is less than 25% the check engine light will not come on; you should drive on and not worry about it.
If the engine runs strong, gas mileage is good, no check engine light, then the O2 sensors are okay, so again, drive on.

 

[mk378]

The incomplete code means that the car has not been driven enough since the last reset for the computer to have full data to make a decision on the cat condition. A reset would be a loss of battery power or clearing all codes through OBD.

After the testing time has been completed, if the cat is found to be OK the incomplete code will clear. If the cat is found to be bad the incomplete code will also clear, but a cat code (almost always P0420) will be set and the CEL will come on.

As for loss of battery power, if the backup circuit is bad the PCM will lose memory every time the key is turned off. This means that incomplete codes will never clear-- it also causes various runnability issues since it can't remember long term calibrations and trims.

The way to test this is to disconnect a sensor to intentionally cause the CEL to come on and set a code. Confirm the code is there. Reconnect the sensor and confirm the CEL goes out but the code is still there. Turn the key off wait a few minutes and restart and confirm the code is still there. This means the memory backup is working. You can then clear the code.

 

[ARCOgraphite]

FIrst, if the front O2 sensor is working properly the car is not running rich.
The O2 sensor has the final say and will bring the mixture to hover around stoichiometric when in closed loop.
The computer is compensating for the difference between what the fuel map expects and what the O2 sensor indicates.
As long as the trim is less than 25% the check engine light will not come on; you should drive on and not worry about it.
If the engine runs strong, gas mileage is good, no check engine light, then the O2 sensors are okay, so again, drive on.

The older Lambda are binary and go HIGH at lower vacuum med -high loading. They only control mixture
at near closed throttle, light load cruise and hot Idle. Their output is considered gospel buy the ECU unless it is way out of range or the heater is seen as open or shorted.

But as you say, usually with good throttle response, low misfire count and good mileage and power systems are good.

but contaminated MAF and wonky EVAP Purge can really make a car run bad with no MIL lit.

- Ken

 

[biomecanoid]

Now I focused on the O2S12 sensor, its range was from 0.75 up to 0.625 so I guess its working. What I don't know is how the 2 sensors should relate to each other.

 

[biomecanoid]

The incomplete code means that the car has not been driven enough since the last reset for the computer to have full data to make a decision on the cat condition. A reset would be a loss of battery power or clearing all codes through OBD.

After the testing time has been completed, if the cat is found to be OK the incomplete code will clear. If the cat is found to be bad the incomplete code will also clear, but a cat code (almost always P0420) will be set and the CEL will come on.

As for loss of battery power, if the backup circuit is bad the PCM will lose memory every time the key is turned off. This means that incomplete codes will never clear-- it also causes various runnability issues since it can't remember long term calibrations and trims.

The way to test this is to disconnect a sensor to intentionally cause the CEL to come on and set a code. Confirm the code is there. Reconnect the sensor and confirm the CEL goes out but the code is still there. Turn the key off wait a few minutes and restart and confirm the code is still there. This means the memory backup is working. You can then clear the code.

Regarding power reset I changed the battery on 23/03/21

 

[biomecanoid]

So what is the recommended course of action now ? starting from the simple/cheap fix going up to the expensive/complicated fix.


A: Replacing the oxygen sensor ?

B: ?

C: ?

What's next ?

 

[mattd]

Now I focused on the O2S12 sensor, its range was from 0.75 up to 0.625 so I guess its working. What I don't know is how the 2 sensors should relate to each other.

0.7V on the upstream o2 is also reporting a rich condition. It’s trying to compensate by the -15% fuel trims you see. I would look at the engine, whether that be a MAP/MAF issue, or uncontrollable purge, excessive fuel pressure, a leaking fuel injector or a mechanical issue

does the car accelerate properly?

 

[biomecanoid]

0.7V on the upstream o2 is also reporting a rich condition. It’s trying to compensate by the -15% fuel trims you see. I would look at the engine, whether that be a MAP/MAF issue, or uncontrollable purge, excessive fuel pressure, a leaking fuel injector or a mechanical issue

does the car accelerate properly?

Yes the car accelerates very fast for a tiny 1000cc engine ( even spins the tires ) and top speed is 160KM on the highway. I guess the little Daihatsu has a bit of Herbie in its heart.

 

[biomecanoid]

0.7V on the upstream o2 is also reporting a rich condition. It’s trying to compensate by the -15% fuel trims you see. I would look at the engine, whether that be a MAP/MAF issue, or uncontrollable purge, excessive fuel pressure, a leaking fuel injector or a mechanical issue

does the car accelerate properly?

So what should the relation of OS211 and OS212 should be. What is considered ideal ?

 

[biomecanoid]

FIrst, if the front O2 sensor is working properly the car is not running rich.
The O2 sensor has the final say and will bring the mixture to hover around stoichiometric when in closed loop.
The computer is compensating for the difference between what the fuel map expects and what the O2 sensor indicates.
As long as the trim is less than 25% the check engine light will not come on; you should drive on and not worry about it.
If the engine runs strong, gas mileage is good, no check engine light, then the O2 sensors are okay, so again, drive on.

Car is indeed running strong. Gas mileage is not that good for a small car, I remember the fuel consumption was 8lt/100km, last time I checked was 10lt/100km, I don't have an Engine Check Light.

The way I understood that the car was running rich was the black mark on the ground that the exhaust leaves on startup and the bad fuel economy. Then I tried to verify my findings with the readings of the OBDII.

You believe the car is not running rich ?

 

[Popsy]

That's terrible fuel economy, within the range of my 1,5L Mitsubishi.
I would be indeed inclined to think it is running rich, but I don't know how to "test, not guess" with the measures you presented.

When the Barchetta presented similar symptoms, I replaced the O2 sensors and everything went back to normal (Or course it doesn't have easily readable OBD data)

 

[biomecanoid]

That's terrible fuel economy, within the range of my 1,5L Mitsubishi.
I would be indeed inclined to think it is running rich, but I don't know how to "test, not guess" with the measures you presented.

When the Barchetta presented similar symptoms, I replaced the O2 sensors and everything went back to normal (Or course it doesn't have easily readable OBD data)

What additional info you would require ?

 

[Popsy]

What additional info you would require ?

I meant the problem is not with the data presented, but with said data treatment abilities on my side

 

[biomecanoid]

I meant the problem is not with the data presented, but with said data treatment abilities on my side

Isn't the fact that the exhaust spits black soot on startup a dead giveaway that the car is running rich ?

 

[biomecanoid]

That's terrible fuel economy, within the range of my 1,5L Mitsubishi.
I would be indeed inclined to think it is running rich, but I don't know how to "test, not guess" with the measures you presented.

When the Barchetta presented similar symptoms, I replaced the O2 sensors and everything went back to normal (Or course it doesn't have easily readable OBD data)

To be honest sometimes I drive like I stole it

 

[mk378]

On startup an EFI system runs open loop which is intentionally rich just to keep it running. In open loop the O2 sensor is not monitored.

As the coolant temperature approaches the designed operating temperature it changes to closed loop and uses the O2 sensor to trim the fuel mixture. You should look at the ECT realtime to be sure it is actually warming up. If it stays in open loop you get poor mpg.

Also do what I said before to confirm the memory is working.

 

[biomecanoid]

On startup an EFI system runs open loop which is intentionally rich just to keep it running. In open loop the O2 sensor is not monitored.

As the coolant temperature approaches the designed operating temperature it changes to closed loop and uses the O2 sensor to trim the fuel mixture. You should look at the ECT realtime to be sure it is actually warming up. If it stays in open loop you get poor mpg.

Also do what I said before to confirm the memory is working.

I believe that memory is working since I have only 1 INC reading out of 6 ( if I remember correctly ). If the car's memory was erased when turning the key off all 6 entries would be INC.

 

[biomecanoid]

On startup an EFI system runs open loop which is intentionally rich just to keep it running. In open loop the O2 sensor is not monitored.

As the coolant temperature approaches the designed operating temperature it changes to closed loop and uses the O2 sensor to trim the fuel mixture. You should look at the ECT realtime to be sure it is actually warming up. If it stays in open loop you get poor mpg.

Also do what I said before to confirm the memory is working.

It is closing you can see it in my previous pictures.

 

[LazyDog]

Look at this picture it shows how read O2 sensors

 

[biomecanoid]

Look at this picture it shows how read O2 sensors

So mine is narrow band correct ?