Disabling LTFT for good??

[5_Liter_Eater]

I like STFT closed loop no matter the application. That way I don't have to worry about positive LTFTs adding to the PE. The STFTs remain intact through ignition cycles and allow for +-25% fueling error which I know I will never need. In my opinion, on a well tuned car there is no need for LTFTs.

Also, open and closed loop have no correlation to MAF and SD.

[Ben Charles]

Great info guys, I appreciate it.

[copley87blazer]

Thanks Bill trying to learn what I can were I can. So I can disable my ltft and my comanded afr will be what I set it at in pe.

[RACINGVORTEC5.3]

hi ive been looking at your posts and im doing a 99 5.3 vortec swap into a 85 blazer im perty new to tuning i have hp tuners and would like to know if i can remove the maf and o2s with hp tuners

[Ben Charles]

You can do many things with MAF and o2's depends on when you need to do certain things. You can set the MAF to 0 freqeuncy or unplug it. If you do some quick searches more info will come up.

[RACINGVORTEC5.3]

well you can eliminate maf and all four o2s knock sensor hvac leaving a clean install with not to many wires a good tune and you got yourself a hot rod

[oakley6575]

well you can eliminate maf and all four o2s knock sensor hvac leaving a clean install with not to many wires a good tune and you got yourself a hot rod

I don't see any reason to delete all the o2 sensors. Why wouldn't you want the computer to use stft's?

[que4dog]

Good info. Question, when the stfts are positive say +12. Do I just multiply 12% fuel to that area on the maf.

[5_Liter_Eater]

Yes. Assuming you have disabled ltfts. You use a histogram to plot stft against the maf curve and then copy / paste special: multiply by % right into the maf table in the tune.

[ChevyHighPerformance]

I know this is kinda an old thread, but I was just referred to it. I'd recommend that you should be tuning to get your LTFTs and STFTs to be near zero everywhere. The issue I have with disabling LTFTs is if a failure occurs. For example, if your FPR is starting to fail in a way to decrease you FP and you disable your LTFTs, your STFTs will take care of adding fuel for part throttle fuel correction. However, if you go to WOT, then you run the risk of running unexpectedly lean because you have no LTFT correction to add fuel.

[oakley6575]

But every other day you drive the truck you want LTFT adding to your PE fueling?? I sure don't

[ChevyHighPerformance]

But every other day you drive the truck you want LTFT adding to your PE fueling?? I sure don't

My LTFTs and STFTs hover very close to zero. So at PE, it is not an issue.

[WS6FirebirdTA00]

Maybe. You just need to hope they lock positive for WOT. They are dummies in PE as they just lock on the last value for that FTC. So if fueling looks 2% lean at part throttle and goes 20% lean at WOT, you will still end up 18% lean.

I have never really seen them reliably add a correct amount of fuel at WOT for safety. I have logged cars that have had issues and while the trims helped CL the locked in values didn't do anything good for PE.

[ChevyHighPerformance]

When I said hover, I meant +/- 1.5% over all RPMs and engine load. If either extreme LTFT value is used for PE, I'm OK with a +/-1.5% uncertainty in my WOT A/F.

Only using STFTs is not unheard of in cars in Europe, especially one's Bosche was involved in.

Here are some other things that would have caused LTFTs to add fuel at part throttle that leave you unprotected at PE with LTFTs disabled:

1) Dirty MAF causing less air to be read.
2) Throttle body gasket leaking air
3) PCV line behind throttle body leaking air
4) Intake manifold gasket leaking air
5) Partially clogged fuel injector
6) PCV line between MAF and throttle body leaking air
7) Brake booster line leaking air
8) MAP sensor O-ring/gasket leaking air
9) Fuel pressure regulator regulating low pressure
10) Weak fuel pressure pump
11) Clogged fuel filter

Granted that many of the air leaks become less of an issue at WOT when the intake manifold is running closer to atmospheric pressure. However, the fuel related items become more of an issue at WOT because at part throttle intake manifold vacuum helps fuel flow. At WOT when vacuum is much less and fuel flow demand is higher, fuel delivery problems become a larger factor.

We can kindly agree to disagree. Disabling LTFTs is just not for me.

[WS6FirebirdTA00]

Doesn't matter if they are 0, 1 or 2, they can easily lock in higher and I have seen that many times. I have not seen anything like you list above.

Those leaks you list are so small that it is a low % of air at WOT. I actually went from a closed PCV system and then put a breather on the car (with the MAF) and since the volume of air was so small I didn't even see my fueling change. The other fueling items you list will most certainly still give problems at WOT with or without LTFTs enabled since outside of PE it will be less of an issue.

It is a matter of opinion and you are fine to have your own, I am not arguing that. I prefer proper fueling vs. incorrect fueling from the computer. This way I know my fueling is what I command and not trying to dip in the 11's. I have seen many different cases and taking into consideration all the possibilities I still feel better with LTFTs disabled. Too many times I have seen people complain about lack of response, loss of power, etc and it ends up being the trims needed a reset because some odd ball +10% trims were learned at WOT. I have never seen any other type of failure that the LTFTs helped as a "safety".

[obzidian]

So, with the LTFT's diabled, do you tune your MAF/VE with the STFT's or with the wideband? (AFR Error %)

The car im working on now (maggie ls1, pulley swap 3.0", shorty headers) has some really LAZY front O2's. First they playing nice (LTFT's +/-2%) then the O2's get "stuck" for about 3-5 seconds either lean (both banks) or rich (both banks) and mess everything up. I'm thinking that perhaps the shorty headers are causing a similar issue with the O2's like headers and maybe the car has an exhaust leak somewhere.

[WS6FirebirdTA00]

Wideband, then verify the o2s are setup properly for the STFTs.

Mess with your proportional fuel if you are sure the sensors are good.

Another example why I don't like LTFT, if you get an o2 to rail (which is common on aftermarket headers) it can get way off quick.

[obzidian]

By "rail" do you mean they stick at a certain MV instead of oscillate up and down? Cause that is exactly what I'm getting. The Trims would get "perfect" and suddenly the O2's will stick to 886mv for a few seconds and blamo! My LTFT's are diving to +/-10.

[WS6FirebirdTA00]

Yes.