Why do trims need to lock onto 0?

[GTPpower]

One thing I've never really understood.

As long as you are getting the afr you are shooting for, what does it matter where they lock at? Does it help the car to consistently hit the afr you are shooting for more accurately?

[murphinator]

One thing I've never really understood.

As long as you are getting the afr you are shooting for, what does it matter where they lock at? Does it help the car to consistently hit the afr you are shooting for more accurately?

on 3800's the trims carry into any wot situations so you will continue to add or subtract the amount of fuel (rich or lean) indicated in the trims

[GTPpower]

Yeah, but why does it matter if you are still hitting your desired 11.5-7?

[TommyGloves]

My SSEi has a range of 0 to +3.1 at WOT. I've been running the same dialed in MAF curve for 3 months now. I quit chasing "0" trims and found that the carried over fueling adjustment does not have a significant impact on my WOT fueling. My average Commanded AFR vs. WB AFR is within +/- .1 AFR regardless of locked in LTFT (0 to +3.1 LTFTs).

From my experience, as long as your Commanded AFR is within the accuracy specs of your WB AFR, you should be ok. (At least that what I found that works for me and my car.)

[driftnpow]

fuel trims are an O2 error correction based on end exhaust gasses, its a percentage of the commanded injector duty cycle.. if its + its adding fuel to whats commanded by the constant if its - its telling to cut down on the fuel injected,

if your o2 is of age, it gets slower, bosch have detailed writeups on this but by the end of its life it "sees" the engine running as lean, adding fuel. a built in failsafe if the sensor were to fail prematurally.
now comes to fuel trims the main ones to deeply consider are your long term trims. if theyre out, look at the relevent cells, coordinate to the appropriate tables and make the adjustments needed to bring the corrections as close to 0% as you can

[GTPpower]

Thanks for the comments everyone. I've been tuning for a few years, and I realize what is going on when the trims are either positive of negative. I can understand the benefits of getting the trims close at cruise. But, I still see no benefit of getting them to lock onto 0 at WOT as long as you are hitting your correct AFR. Anyone know why this has become a standard?

[BlackGS]

My SSEi has a range of 0 to +3.1 at WOT. I've been running the same dialed in MAF curve for 3 months now. I quit chasing "0" trims and found that the carried over fueling adjustment does not have a significant impact on my WOT fueling. My average Commanded AFR vs. WB AFR is within +/- .1 AFR regardless of locked in LTFT (0 to +3.1 LTFTs).

From my experience, as long as your Commanded AFR is within the accuracy specs of your WB AFR, you should be ok. (At least that what I found that works for me and my car.)

x2. It is more important to tune PE with a wideband, not trims. I stopped trying to get an exact lock on trims as well since it does not impact AFR. I also have found that my trims don't always "lock" in PE. I have seen instances where the trim will start around -5 in PE, then jump up to -1, then back to -5 right before exiting PE. AFR stays flat throughout.

[GTPpower]

Cool. I've never seen them move while in PE, but don't doubt it. I usually try to get them close, especially during cruise, but I never really understood why they needed to lock onto 0 as long as you have the correct afr. Thanks for the info.

[bilemke]

If multiple learned cells are experienced under PE, multiple learned fuel trims could be seen.

If our cars use fuel trims in PE, it is something potentially serious..

Say you command 12:1 AFR with a 0 trim and hit 12:1 actual AFR.. Great.. Next run you have a fuel trim of -1 (percent).. That mean you are now really commanding 12:.99 (about 12.12:1).... Go a bit further.. -5 percent... 12:.95 = 12.63:1....

[thebeewantsboost]

i've wondered this forever. why does it even help in cruise??
Bilemke.
if you command 12.1 and get 12.1 with no fuel trims. Why would you get a fuel trim of -1. sorry but your post totally lost me

[Mobile Chassis Dyno]

Using the STFT Maf histogram you can easily get your LTFT's within 1% at idle and cruising which will should give you a LTFT of Zero in P/E every time. I have tuned a handful of 3800's this year using the histogram and the LTFT's stay between 0 and 0.8%.

If you have a LTFT that is something other then zero in P/E then you are not tuned.

[bilemke]

i've wondered this forever. why does it even help in cruise??
Bilemke.
if you command 12.1 and get 12.1 with no fuel trims. Why would you get a fuel trim of -1. sorry but your post totally lost me

Because with the pathetic number of fuel trim cells our v6 setups have, the cell might learn a value when not under PE that might later be used under PE..