Car: 2010 LNF w/ Downpipe, Intake, and Hot Side Charge Pipes

Dyno tuned locally through HP Tuners.

I am having issues with my STFT being erratic. They fluctuate between +20 and -20, but do not last enough to throw off my LTFT. My LTFTs hover between +/- 3.

The STFT fluctuations typically happen when accelerating or decelerating, especially when near DFCO kick in.

Any ideas what this may be?

 

dfco?

 

ur maf could be effed. did u try smoothing it out at all in tune? I know iv had erratic stft, once it was maf, second time it was bad gas. did u fill ur car recently?

 

DFCO is decel fuel cut off

My tuner supposedly did all the smoothing and calibrating. Its been like this since he tuned it, so it isnt the gas.

 

Ah lol. No codes yet?

 

If it's only on transition and not affecting your long term trims, why worry about it? How are the trims during steady state?

 

They routinely go beyond 5% but nothing too crazy like 20%.

I am concerned because this does not seem normal.

No codes.

 

Do you have a log of it?

Generally it means your fuel trims need to be tuned more.

Could also mean you have an air leak somewhere but I'd look at the tune first.

 

more than 5% is nothing, that's the system doing it's job.

Log the fuel trims in a histogram map and see which cells are hitting higher numbers, then compare to that section on your MAF and run some datalogs to adjust.

It's not going to change anything though. Car will run the same regardless.

Just re-read your initial post, it says dyno tuned. Did you street tune? There's no way to tune all your fuel trim/maf cells on the dyno without spending hours. most people get a couple full throttle pulls to maximize power, and that's your tune. That's the primary reason I prefer to tune cars on the road opposed to the dyno. If i'm driving the car, I can hit every cell enough to build a decent maf tune.

 

We did street tuning twice already. Doesn't seem to help much with the spikes.

I've boost leak tested the car downstream of the compressor at 25#'s, and found 0 leaks. The car has had a boost leak previously so I know how that will affect the fuel trims. This is not characteristic of a leak.

 

There are no leaks, fuel trims move around, it's why they are there in the ECU. To help control excess fuel for emissions reasons. If you can't get them any smoother via proper MAF tuning, i'd suggest comparing them to another car in your area with the same mods. It may be normal and you're expecting perfect smoothness where it isn't possible. Or you could have a MAF or primary O2 that isn't responding fast enough like it was when new.