Hey guys, so as the title says, my fuel trims and wideband are reading totally different results; I'm aware that fuel trims aren't super accurate for tuning, but my wideband is telling me that my AFRs are spot on, whereas a bunch of cells in my fuel trims histogram are reading right around -10. I'd appreciate it if someone could point me in the right direction, I feel like I'm chasing my tail with this one

 

The -10 you are seeing is "after the fact" as in that is what the PCM has pulled already. So that means the PCM is correcting by 10% to get you to what you are seeing on the WB. Try turning off closed loop and see what it looks like. I'll bet it will show that same 10% rich condition on the WB suddenly.

My suggestion would be to simply use the STFT's to tune that particular spot, because the PCM is going to do it anyway. Reduce those cells by 10%, MAF or VE, whichever one you are using and the WB should continue to read the same. It appears that the STFT's are actually doing their job and keeping AFR pretty close to stoich.

Also, make sure your LTFT's are off while tuning with STFT's.

 

U cant really tune using both.

If u have a wideband force ecu into open loop and tune using wideband error %.

If using stft, just use the wideband to fine tune wot only. Once u get your stft dialed in it will all come together.

Once u get to around 2-3% error, your tune is pretty much dialed in. Very hard to get much better than tht!

 

So I ran into an issue, I turned off my stfts, and my wideband is still reading pretty normal, but now I'm losing power down low in the rpms, probably about 1500 rpm it just falls on its face. Side note, my STFT histogram is still being populated, should it be empty if they are actually disabled?

 

Not to sidetrack the thread, but at what point should I be concerned about IATs? They got up to 120 today and I just realized that the ECU is pulling out 6+ degrees of timing at that temperature. Can I safely lower the amount that it takes out?

 

I usually start pulling timing around 100iat. Maybe around 4* at 120. This is playing it safe.

If its an aggressive tune trying to get everything out of it. Maybe 2* at 120 iat.

 

Go into your scanner and reset fuel trims and command open loop to make sure stft are off when tuning via wideband. If your tuning with a wideband and stft are moving fueling around youll be chasing your tail. If they are completely off o2s will be dead and 0 in histogram. Same as if you were wot open loop.

 

Alright, I'm going to try and fully turn off the fuel trims tomorrow and see how it goes. As far as IAT goes, I guess I'll have to find a way to bring the temps down; I figured the stock intake was in a decent enough spot where it wouldn't be an issue, but I guess not haha

 

Usually they do heat soak while at idle. A good cai will lower temps to about ambient while cruising.

 

It's not just at idle, Its consistently 30-40 degrees above ambient, even while moving, and sadly, I don't think an aftermarket CAI is an option for me, my engine is in a chevy express van, not too many aftermarket performance parts made for them haha. I was thinking of routing my air intake down through my bumper(kind of like the ambulances with air horns in the bumper. But that's a little far out of my skill set and apparently most companies won't chrome plate a modified bumper

 

One will go nuts trying to make trims perfectly in agreement with wideband calibrated maf/ve tables. Just shoot for + - 5% stft, even stock setups range a few % in positive and negative trimming.
Also, further back located narrowband o2 sensors compared to factory distance from the engine such as when going from oem exhaust manifolds to longtubed headers, will have a part in trim values and can add to this confusion/disagreement.

 

I have factory exhaust manifold, so that shouldn't be a problem. But I can't seem to get my STFTs to stay quiet. I tried forcing closed loop in the log, but I'm still seeing STFTs in the histogram, my LTFTs gave me no issue when I shut them off, they've stayed at 0 ever since. Anyone have any idea what my problem is?

 

Set o2 readyness test to around 280*
Disable decel fuel cut off 280*
Closed loop enable temp to 280*

This should disable stft's. Save this as a seperate tune file. Revert back to your other one once tune is finished.

 

Alright I just made the new tune, I'll upload it tomorrow and give it a shot. I appreciate all of the help you guys have been!