Fuel trim values?
#1
05-20-2014, 03:20 PM
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Fuel trim values?
Hello, I was wondering if anyone knew what the fuel bank trim values should be or what is acceptable. I have the SCT X4 tuner and was watching the numbers.
2002 5.4L DOHC engine
My Long term banks are stable @ 1.0
but my short term fuel trim are a bit different
Bank 1 @ 1.0 and Bank 2 fluctuates from .89 to 1.03
Is that within normal range?
I am guessing that could be caused by low compression in one cylinder?
Wasn't sure if it could be caused by something else since the other three are all stable.
Thanks!
I figured since this is tuner data interpretation it was proper to post here. If not sorry.
2002 5.4L DOHC engine
My Long term banks are stable @ 1.0
but my short term fuel trim are a bit different
Bank 1 @ 1.0 and Bank 2 fluctuates from .89 to 1.03
Is that within normal range?
I am guessing that could be caused by low compression in one cylinder?
Wasn't sure if it could be caused by something else since the other three are all stable.
Thanks!
I figured since this is tuner data interpretation it was proper to post here. If not sorry.
Last edited by sleuthsnoopy; 05-20-2014 at 03:23 PM.
#2
05-21-2014, 12:14 AM
As I recall, and someone will correct me if I'm wrong, the "ideal" fuel trim value is 1.0. The "long term" values are established over time, as the PCM learns how to adjust for various demands. I think they're somewhat like an "average".
Now, short term trims are more like instantaneous values, and they fluctuate as the readings from the O2 sensors feed back to the PCM, which in turn, adjusts the air/fuel ratio to achieve the ideal value. This is a bit of a continuous "dance", and you should see values around the 1.0 ideal, but you will see numbers above and below the ideal as the two systems work together to get things right. Again, as I recall, a value below 1.0 is rich and one above 1.0 is lean.
As I said, someone will correct me if I got this wrong, but I don't think you have a thing to worry about.
- Jack
Now, short term trims are more like instantaneous values, and they fluctuate as the readings from the O2 sensors feed back to the PCM, which in turn, adjusts the air/fuel ratio to achieve the ideal value. This is a bit of a continuous "dance", and you should see values around the 1.0 ideal, but you will see numbers above and below the ideal as the two systems work together to get things right. Again, as I recall, a value below 1.0 is rich and one above 1.0 is lean.
As I said, someone will correct me if I got this wrong, but I don't think you have a thing to worry about.
- Jack
#3
05-21-2014, 03:24 PM
Senior Member
As I recall, and someone will correct me if I'm wrong, the "ideal" fuel trim value is 1.0. The "long term" values are established over time, as the PCM learns how to adjust for various demands. I think they're somewhat like an "average".
Now, short term trims are more like instantaneous values, and they fluctuate as the readings from the O2 sensors feed back to the PCM, which in turn, adjusts the air/fuel ratio to achieve the ideal value. This is a bit of a continuous "dance", and you should see values around the 1.0 ideal, but you will see numbers above and below the ideal as the two systems work together to get things right. Again, as I recall, a value below 1.0 is rich and one above 1.0 is lean.
As I said, someone will correct me if I got this wrong, but I don't think you have a thing to worry about.
- Jack
Now, short term trims are more like instantaneous values, and they fluctuate as the readings from the O2 sensors feed back to the PCM, which in turn, adjusts the air/fuel ratio to achieve the ideal value. This is a bit of a continuous "dance", and you should see values around the 1.0 ideal, but you will see numbers above and below the ideal as the two systems work together to get things right. Again, as I recall, a value below 1.0 is rich and one above 1.0 is lean.
As I said, someone will correct me if I got this wrong, but I don't think you have a thing to worry about.
- Jack
You'd rather see negative numbers than positive numbers.
#4
05-21-2014, 07:54 PM
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Thanks. I just wasn't sure if the 1.0 was the percentage equating to 100%.
The Lincoln dealer said that #7 cylinder is dead or dying and their graph shows it at only 5% loss of compression. The reason I took it there is cause of a slight shake like miss that you feel in the body of the truck but doesn't jerk when in drive but #7 would be on Bank 2 and the fluctuation I see on Short term is Bank 1 so again I am baffled.
today the readings were LT bank 1- 106 Bank 2- 1.03 which eventually and slowly came to both at 1.03
St bank 1- 0.89-1.03 St bank 2- 1.03
So the numbers to strive for from what I understand from the replies is .95?
Being as 1.03 would mean more air and less fuel going to the O2 sensors and .90 would be more fuel going to the O2 sensors right?
Also my mpg has gone way down since I tuned the truck with a economy tune. I am guessing that the cpm isn't registering the numbers correctly as it went from 12 to 8.8. I just filled the truck up to do a manual calculation but I don't drive much and so far only 20 miles driven so it may be a few days fro me to get that calculation done.
Anyone have issues with tuning and the truck mpg computer?
The Lincoln dealer said that #7 cylinder is dead or dying and their graph shows it at only 5% loss of compression. The reason I took it there is cause of a slight shake like miss that you feel in the body of the truck but doesn't jerk when in drive but #7 would be on Bank 2 and the fluctuation I see on Short term is Bank 1 so again I am baffled.
today the readings were LT bank 1- 106 Bank 2- 1.03 which eventually and slowly came to both at 1.03
St bank 1- 0.89-1.03 St bank 2- 1.03
So the numbers to strive for from what I understand from the replies is .95?
Being as 1.03 would mean more air and less fuel going to the O2 sensors and .90 would be more fuel going to the O2 sensors right?
Also my mpg has gone way down since I tuned the truck with a economy tune. I am guessing that the cpm isn't registering the numbers correctly as it went from 12 to 8.8. I just filled the truck up to do a manual calculation but I don't drive much and so far only 20 miles driven so it may be a few days fro me to get that calculation done.
Anyone have issues with tuning and the truck mpg computer?
Last edited by sleuthsnoopy; 05-21-2014 at 07:58 PM.
#5
05-22-2014, 11:56 AM
A value less than 1.0 means you are operating in a "richer" condition than stoichiometric, which means you might be pumping unburned fuel out the tailpipe. More than 1.0 and you're lean, which can lead to higher temperatures and if bad enough, engine damage. The 1.0 value is not 100%, it's just a number that represents an "ideal" air/fuel ratio for complete combustion.
In practice, you never actually achieve a stoichiometric air/fuel ratio, you only come close. Your numbers to me seem close. The 0.95 value you mentioned might be what you'd see or want if your engine was under load, but probably not in a stable cruise condition.
A 5% loss in compression in one cylinder is not too much, in my opinion. I'm not sure you'd feel it. But, it could be telling you you are heading for a ring job.
The drop in MPG is possibly due to an error in the Tire Size or Gear Ratio that the PCM is using now that you've installed your tune. Is there a way to check those with the X4?
- Jack
In practice, you never actually achieve a stoichiometric air/fuel ratio, you only come close. Your numbers to me seem close. The 0.95 value you mentioned might be what you'd see or want if your engine was under load, but probably not in a stable cruise condition.
A 5% loss in compression in one cylinder is not too much, in my opinion. I'm not sure you'd feel it. But, it could be telling you you are heading for a ring job.
The drop in MPG is possibly due to an error in the Tire Size or Gear Ratio that the PCM is using now that you've installed your tune. Is there a way to check those with the X4?
- Jack
#6
05-22-2014, 03:59 PM
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there is a way to adjust the tire size and gear ratio but I kept it at stock.
Funny thing is that on the x4 gauges you can adjust where you want the gauges and which ones. On a whim I moved the bank 2 fuel trim gauge to where I had bank 1 and the same thing happened fluctuation. so I moved both of them and they are exactly the same. each fluctuating within the same specs. So I am guessing it was just an error in the device and now both gauges are in different spots of the X4 they are good.
Trial and error I guess.
I am guessing that the engine is fine because the engine doesn't seem like its missing nor codes and after looking at my body mounts (all deteriorated majorly and falling apart) I am replacing all body mounts and going to do the engine mounts as well, hopefully the slight shake will be gone!
Funny thing is that on the x4 gauges you can adjust where you want the gauges and which ones. On a whim I moved the bank 2 fuel trim gauge to where I had bank 1 and the same thing happened fluctuation. so I moved both of them and they are exactly the same. each fluctuating within the same specs. So I am guessing it was just an error in the device and now both gauges are in different spots of the X4 they are good.
Trial and error I guess.
I am guessing that the engine is fine because the engine doesn't seem like its missing nor codes and after looking at my body mounts (all deteriorated majorly and falling apart) I am replacing all body mounts and going to do the engine mounts as well, hopefully the slight shake will be gone!