Hello,
I just checked my car with the OBDII tool and found the Long term fuel trim to be -15% when parked idling.
I do remember both short and long term fuel trim being at 0% a few days ago.
I don't believe this is normal, Anything I can do ?
Thank you
Chris
Vehicle: 2006 Daihatsu Sirion 1000cc
mileage?
a negative value means the computer is trying to take away fuel. In other words your mixture is too rich (too much fuel or not enough air).
Did you do anything to the car between now, and when the fuel trim was normal? Is the air filter clean?
On 23/05/2021 both short and long fuel trim was at 0%.
Air filter is clean yes, ( 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
you should wait a while after the fuel system cleaner is complete
You are saying this is normal ? Today I refueled, so I went thru a full tank of gas with the STP
I’m saying the cleaner could be throwing things off. Just keep an eye on it for now
A couple things stand out. From your 1st screenshot we see that the fuel system is in Open Loop.
Your ECT is at 62°C (143.6°F). Generally the fuel system won't switch to Closed Loop until the ECT (engine coolant temperature) is over 160°F. But that should occur in just a few minutes of driving so on your next ride hook up your scanner in Live Data and make sure that ECT sensor is reporting the correct ECT when the vehicle is warmed up and that the FUELSYS1 data switches to Closed Loop.
If the ECT sensor is reporting Lower than the actual ECT (in Closed Loop) you'll run rich.
You didn't say what you're driving but look at the MAF sensor reading at idle. (if it has a MAF). It should be around 1g/s for each liter of engine displacement. So if you have a 3.0 Liter engine your MAF should be reading around 3g/s at idle. If it's reporting much more than that (at idle) you'll run rich.
Thanks for your help, I am driving a 2006 Daihatsu Sirion 1000cc. I posted some new info have a look
You'll want to start with the basics and with things that are probably due for preventative maintenance anyway.
The stuff that could possibly cause rich running.
Weak spark plugs. Maybe throw a set of new plugs at it. (cheap enough)
Test the coils with an HEI Ignition Spark Tester. It's less than $20 bucks and you have a 15 year old car. Use it, then throw it in your tool box. You'll be needing it again if you keep the car. See if you have a weak coil.
Definitely replace your PCV valve and its hose. If it's sticking or partially clogged, or if the hose is so worn that it's collapsing under vacuum, the computer will be adding fuel for air/blowback vapors from the crankcase that never make it into the intake manifold. Then the upstream 02 sensor will read the rich condition and the computer will lean out the air/fuel mixture until the upstream 02 sensor is happy.
If the issue persists then buy an inexpensive fuel pressure gauge. (around $25 bucks online). You'll be able to determine 2 things. First, if your fuel pressure regulator is faulty. Second, if you have a leaky injector. Youtubes on how to do that.
So new plugs, PCV valve, PCV Hose. (cheapest parts on the car).
2 new inexpensive tools. Incidentally, if you have any Chain Auto Parts Stores around you they probably have a tool loaner program where you buy the fuel pressure gauge and then return it within the time allotted, they give you your money back. So you're only out the cost of the HEI ignition spark tester.
But you've determined if you have any bad coils, you've removed any weak plugs from the equation. or excessive fuel pressure at the fuel rail (delivering too much fuel in the injector pulses) or if a leaky injector is causing the problem, or if the PCV valve/hose was causing the problem.
Also, and I quote, "smack your catalytic converter and listen if it rattles".
Thank you
Photos of the readings from the scanner:
how long was it running when you captured these?
Is anything else weird in my OBDII readings ?
Any ideas ?
I asked you above how long was the engine was running when you captured the OBD data?
Hhm 5 -10 min I guess like when I was perfect long fuel trim
ok next time take it for a drive and let it get up to temp first
Will try that today as I come home from work
Arriving home after 30min drive and idling 10min:
Arriving home after 30min drive and idling 20min:
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
I think your downstream oxygen sensor (O2S12) reading is far too low. The sensor might be bad, but that still wouldn't affect fuel trims.
The other possibility is that your catalytic converter has failed. That could affect the sensor AND your fuel trims, so I would look into that.
Is your OBD tool able to graph the O2 data over a period of time? That would help a lot with diagnosis.
here's some background on how that stuff works: https://www.fixdapp.com/blog/oxygen-sensor/
I have the Creader 3001 sadly can not do graphs.
smack your catalytic converter and listen if it rattles
Hmm would it rattle as I turn off the engine ? Cause I think there is a rattle then but I don't know if its the catalytic converter . I will try to record the sound of the exhaust.
So what is the recommended course of action now ? starting from the simple/cheap fix going up to the expensive/complicated fix.
According to what you said I should start with :
A: Replacing the oxygen sensor
B: ?
C: ?
Whats next ?
no that's not what I said. Read it again.
So then I am left with only one plausible fault, the catalytic converter itself
So what are my options now ?
are you even reading everything?
https://carkiller.com/scottykilmer/qa/obdii-longft1-15-at-idle/#post-114723
OK so there recommended parts to check are:
1.Spark Plugs
2.Coil
3.PCV ( in fact I have already ordered that online a week ago )
4.Fuel pump / Fuel Pressure Regulator
What about: Purge Valve, MAP Sensor, Oxygen Sensors ? could they be causing my issues ?
Here is some more data:
SPARKADV:
Fuel Trim and O2 Sensor videos
Does the above info help in any way ?