Low calc_vet values vs LTFT

[robof16]

Just updating a tune and the values produced by calc_vet are much lower than expected.

Example (6.0L with mild cam): In the idle area (800 RPM, 60 kPa) for instance, the log produced VE (1.143) is around 60% lower than my VE table (1.817) with LTFT's close to zero. Same issue at low RPM cruise (2400 RPM, 65 kPa), but the differential is much less, around 17%.

As RPM and Load increase, the differential decreases so, by 4000 RPM, the difference is negligible.

[joecar]

Are the LTFT's swinging or flat...?

Please post a screenshot showing LTFT's.

[robof16]

Thanks for the reply Joe.
24716
LTFT's are flat.
Two things:
1. I'm sure I'm not saying this correctly but, I was under the impression that LTFT's reflected a difference between commanded EQ and the VE table, but I see that it's between EQ and the MAF frequency, correct?
2. My "mild" cam change could be affecting the VE table WAY more than I anticipated. It has a tighter LSA than the previous cam and less exhaust duration. New (212/212, .553, 107 LSA) vs Old (212/218, .553, 112 LSA). 60% difference at idle though does seem like a lot.

[pinstripebob]

LTFT should be based on MAF and VE compared to feedback from your upstream oxygen sensors. Normally, VE and MAF are blended up to a certain RPM, unless that has been changed in your tune. It's possible this was changed if you're doing CALC.VET or CALC.MAFT. That's my understanding, I could be mistaken.

Take a look at B0120 to verify.

In my experience, VE tables are generally quite low in the idle area with a cam. Aftermarket cams are not efficient at low RPM, so they don't need as much fuel. It's also hard to get good data at low RPM from your O2 sensors since there will be some unburned fuel at low RPM which will skew your results.

I will say that numbers and smoothness of your tables should not be the driving factor in your tuning. If the engine is consistent, and runs well, don't try to get nice smooth tables or a factory appearing VE table. Focus more on the results of your tune rather than the appearance of your tune.

With the 107 LSA that thing probably has some pretty good chop, I would imagine it would need lower values around idle in your VE table. 60% is a lot, but if it works then go with it.

[robof16]

Yes, I set B0120 at 400 while logging for CALC.VET.
I haven't failed the MAF to check how it runs SD yet but the VE table is about finished. I plan to run MAF-only for now anyway. You read my mind on the VE table though; it's kinda funky looking compared to stock but I'm getting plenty of consistent data from the logs so I'm sticking with it.
I'm kind of surprised the cam doesn't have more chop, idle characteristics are better than expected at 750 RPM, pretty darn smooth. The lower exhaust duration helps.
Overall, the truck is running great.

[joecar]

If the LTFT's are flat at zero then I suspect that either the NBO2 voltages are not switching or the LTFT's are being rounded up from negative values to zero.

Are any DTC's present...?

Log the NBO2 voltages (HO2S11 and HO2S21) and post picture.

[joecar]

CL LTFT's trim commanded fuel based on whichever air model is currently active (MAF for steady state airmass, VE otherwise).

[robof16]

I misunderstood the LTFT question...they do vary plus or minus a little so I'm thinking the MAF is dialed in pretty close. NBO2 voltages are switching also, everything looks normal to me.
No DTCs.
Thanks for the confirmation on the air model. I guess everything is working as it should, just a little surprised by the Log-produced VE values.