LTFT & STFT Readings
LTFT & STFT Readings My long term fuel trims are running about -10% on both banks and the short term fuel trims are running anywhere from -1.5 to -6% on both banks. Does this seem okay or does this indicate a rich condition.
Launching!
Joined: Jan 2012
Posts: 216
Likes: 1
From: Davisburg, MI
Short:Yes it is running rich.
Long: On my car it takes 20-30 minutes of driving for everything to heat soak and stabilize. The tuning comes in as you log each cell in your VE table and adjust. You are most likely looking at the cells associated with steady cruise.The rest of your tune are probably off by differing amounts. Plus or minus 5% for different weather conditions is good. Within 3% is ideal.
Long: On my car it takes 20-30 minutes of driving for everything to heat soak and stabilize. The tuning comes in as you log each cell in your VE table and adjust. You are most likely looking at the cells associated with steady cruise.The rest of your tune are probably off by differing amounts. Plus or minus 5% for different weather conditions is good. Within 3% is ideal.
It's not running rich. It is having to make adjustments that big to hit the target air/fuel. When your trims max out, you are likely running too rich.
Regardless if it's -10 or -1, the end result is still the same circa 14.7 AFR. It's just telling you that the computer is subtracting fuel because it considers the base tune to be too rich.
Now when you start seeing trims over 15-20% (whether negative or positive) is when you're going to actually be running very rich or lean.
I monitor my car with both a WB and trims. I can play around with the trims all day, but in the end the car is still running 14.7 whether the trims are between -1 and 1 or -8 and 8. That's why as long as you have it within a certain range you should be ok cuz you'll never get them perfect and it doesn't matter in the end.
However, I used to have a bad leak where it caused the trims to read lean, thus dumping alot of unecessary fuel. I saw my trims go to +30 and the WB was reading high 10s so that was a real rich condition.
Launching!
Joined: Jan 2012
Posts: 216
Likes: 1
From: Davisburg, MI
Thanks for the help guys. I just had the o2 sensors turned back on and I've got a diablosport predator to monitor the fuel trims. The trims are reading what I mentioned but it just seems that the car still runs rich. At idle the exhaust will burn your eyes if you stand behind the car. I'm new to all this stuff but you guys are always very helpful.
If you aren't seeing black smoke, your eyes aren't likely burning due to a rich mixture. Lean burns your eyes as well as late timing. Both smell different than rich. My wife could tell the difference, most DIY guys that brought their cars in thought if it smelled, it was rich. Vast majority of the time burning eyes is lean or retarded spark.
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Thanks for the help guys. I just had the o2 sensors turned back on and I've got a diablosport predator to monitor the fuel trims. The trims are reading what I mentioned but it just seems that the car still runs rich. At idle the exhaust will burn your eyes if you stand behind the car. I'm new to all this stuff but you guys are always very helpful.
Russ Kemp
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Verdad Gallardo I had no cats for one year on my 2001 ZO6 with a 234/242 114 cam (G5X3), and couldn't stand the stink, my clothes even retained the exhaust stink. And I had several passengers ask what was wrong with my car as they got headaches from the exhaust fumes.
Installed highflow cats, and no more headaches, watering eyes and no more stink. And your MS4 cam has 18.5* overlap (if the std 111 LSA) vs the 10* overlap with my G5X3. So I know your exhaust smell would be way worse with all that overlap.
Russ Kemp
You need high flow cats to fix the stink. The tail pipe on my stock 2008 G6 is also black. Back in the day with leaded fuel, yes a properly tuned engine would have a light grey tailpipe.
I had no cats for one year on my 2001 ZO6 with a 234/242 114 cam (G5X3), and couldn't stand the stink, my clothes even retained the exhaust stink. And I had several passengers ask what was wrong with my car as they got headaches from the exhaust fumes.
Installed highflow cats, and no more headaches, watering eyes and no more stink. And your MS4 cam has 18.5* overlap (if the std 111 LSA) vs the 10* overlap with my G5X3. So I know your exhaust smell would be way worse with all that overlap.
Russ Kemp
I had no cats for one year on my 2001 ZO6 with a 234/242 114 cam (G5X3), and couldn't stand the stink, my clothes even retained the exhaust stink. And I had several passengers ask what was wrong with my car as they got headaches from the exhaust fumes.
Installed highflow cats, and no more headaches, watering eyes and no more stink. And your MS4 cam has 18.5* overlap (if the std 111 LSA) vs the 10* overlap with my G5X3. So I know your exhaust smell would be way worse with all that overlap.
Russ Kemp
