Fuel trims

[Robot_trainer]

Being an old carb guy where you just threw fuel at it until it ran right, Im trying to understand how this new stuff works and what it all means. I have the Revan 13-6 kit (JLT cold air, Ford racing twin throttle body), Lund 93 octane tune, 170 thermostat, Ngk iridium heat range 7 plugs (changed in the spring). Just to see whats going on I hooked up my Innova scan tool and ran a live data capture for 100 frames. Im looking at the LTFT and STFT as well as Lambda. I looked at them at idle and cruising around at different rpms. Didnt do any big pulls.

At idle I have 0 STFT on both banks but the LTFTs are negative b1 at -16, b2 at -18. Bank 2 is always a couple of percent lower (negative). LTFT is always negative (-12 to -20). STFT is mostly negative, both banks very clost to the same number, lowest being -3, highest being 2.8. Lambdas are very close to each other bank to bank ranging from .928 to 1.019. These are at various rpms and accelerating decelerating. Car runs fine, idles smooth. Pulls like a freight train going down hill. No codes. Do these numbers look right for a tune? Car has roughly 20,000 miles on it.

 

[Catmonkey]

This is a pretty good explanation. Make sure the engine is fully warmed up to operating temperature before you make any assessments.

 

[Robot_trainer]

Best explanation I've seen so far. What puzzles me is the STFT is pretty even between both banks and low, but the LTFT is much higher negative and the Lamdas are very close to 1. Yes, engine was right up to temperature. I went for a short drive before hooking up the scanner.

 

[merkyworks]

This is what I understand about STFT and LTFT

• + engine is lean, wants to add fuel
• - engine is rich, wants to subtract fuel
• Even between banks is good cause that mean all 8 cylinders are homologous
• STFT is basically in the moment demand so 0 or near 0 means your tune is spot on and there aren't any engine issues like a vacuum leak.
• LTFT is trend over time when in closed loop. Closed loop is all the time except right when you start up and from what I have read on some 12's and 13-14's it's even when your WOT, this value is stored in the ECU/KAM.

So 0 STFT is good and -12 to -20 LTFT means your a little rich which is a good given your higher HP output. Lambda at idle should always be hunting so your values are normal. As it was explained to me o2 sensors have ADHD and need to keep busy.

 

[Catmonkey]

I think your tune needs some tweaking, or something else is going on. I would log the car and send it to Lund and see what they have to say.

 

[Robot_trainer]

This is what I understand about STFT and LTFT

• + engine is lean, wants to add fuel
• - engine is rich, wants to subtract fuel
• Even between banks is good cause that mean all 8 cylinders are homologous
• STFT is basically in the moment demand so 0 or near 0 means your tune is spot on and there aren't any engine issues like a vacuum leak.
• LTFT is trend over time when in closed loop. Closed loop is all the time except right when you start up and from what I have read on some 12's and 13-14's it's even when your WOT, this value is stored in the ECU/KAM.

So 0 STFT is good and -12 to -20 LTFT means your a little rich which is a good given your higher HP output. Lambda at idle should always be hunting so your values are normal. As it was explained to me o2 sensors have ADHD and need to keep busy.

This is what I understand about STFT and LTFT

• + engine is lean, wants to add fuel
• - engine is rich, wants to subtract fuel
• Even between banks is good cause that mean all 8 cylinders are homologous
• STFT is basically in the moment demand so 0 or near 0 means your tune is spot on and there aren't any engine issues like a vacuum leak.
• LTFT is trend over time when in closed loop. Closed loop is all the time except right when you start up and from what I have read on some 12's and 13-14's it's even when your WOT, this value is stored in the ECU/KAM.

So 0 STFT is good and -12 to -20 LTFT means your a little rich which is a good given your higher HP output. Lambda at idle should always be hunting so your values are normal. As it was explained to me o2 sensors have ADHD and need to keep busy.

Yeah Im wondering if the tune is intentionally set up to get those LTFT numbers

 

[biminiLX]

You have a Lund tune, so you have SCT handheld like an X4 right?
I'm only familiar with SCT datalogs but same principles.
I'd download SCT live link so you can datalog the way Lund or many tuners would.
Lund tuning will request certain datalogs and review but you're probably ok.The base stock tune and the base 91/93 Lund tunes will usually have the car richer than leaner.
-J