Data Logging: LTFT Interpretation

ViperTony

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So, I've finally gotten around to data logging in preparation for some street tuning. I have my wideband and OBD hooked up to my laptop and using PCMSCAN for logging. This has always worked well for me so I'll stick with PCMSCAN. Did a "general" run today, some street driving, highway, a couple of short pulls here and there. I'm looing at the data maps for LTFT Bank 1 and 2. Not sure what I'm looking at. LOL. What does this mean?

These data maps are showing minimum values for cells (Just wanted to see what the highest (negative) fuel trims were:

LTFT Bank #1
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LTFT Bank #2
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Getting ready to be more involved in the tuning process this time around so if anyone that uses data mapping for tuning, what should I be capturing?

I plan on detailing my tuning journey and hopefully this thread will help folks understand the tuning process better.

Thanks,
Tony
 

EllowViper

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Your PCM is pulling a lot of fuel in closed loop (ERGO THE NEGATIVE VALUES). It hits open loop around 3300 RPMs ergo the zero values at higher RPMs. If you have SCT Pro Racer software, you can enable closed loop at a higher value to see what your fuel trims are above 3200...and/or you log your WB values into PCMSCAN to see your actual AFR as compared to your LTFT. Some actually turn off LTFT and log WB values and adjust fuel tables in those cells accordingly. At any rate, you are on the right path. Now you are able to see what fuel cells need work. If you have SCT Pro Racer, you can get into your fuel tables and make adjustments.
 

ViperTony

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Thanks Ellow. It feels like fuel is being pulled at lower in closed loop. I guess the best way I can explain this is, in this log, say I stomp on the gas at 3300 RPM it's HOLY SH** HANG ON FOR DEAR LIFE. Leading up to that, the Viper feels like it's holding back in closed loop. I plan on getting the Pro Racer software and learning it as best as I can. I'm also working off a tune I had from 2 years ago that wasn't complete. I should reset the PCM to stock and start with that which I'll do this week. Here's a graph I like, kinda shows a few things going on:

AFR Bank 1 on Top
Spark Advance/IAT/Coolant Temp
LTFT1&2
O2 Sensor Voltage (upstream) 1 & 2

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EllowViper

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Old tune? You using a VEC or something? What other mods other than your signature? With that build, that engine should sing. I can't really see the data log. Too small. If you add some timing down low (to a point), that will mofidy your LTFTs as well. Many unknown variables right now. What plugs/gap? Injectors? TBs?, etcetera....
 

ViperTony

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Sorry Ellow. SCT tune initially done by Todd at AC Peformance after I installed the GG heads and cam. Stock Champion plugs not the ECC12LYC but the GenIII ones. Gapped at .030" per GG. I never got around to logging and finishing the tuning with Todd and it wasn't 100%. Will do so soon. Since then, I had my intake ported by GG. That's all that changed since the last tune. Stock injectors, stock tb's, stock fuel system. Engine sings, pulls, scared children. LOL. I'm going to do some logs this week with the stock PCM (no tune) as a baseline. I never did that.
 

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