In transient fueling?

[pknowles]

I'm working on transient fueling to remove lean spikes on throttle entry and throttle exit on my 2001 Silverado 6L with 76mm turbo running on a 2002 Tahoe flux fuel tune. I'm running a MAF tune since the truck drives much better with the MAF. For those that are curious, I'm using a scaled tune and LS7 MAF. I confirmed the issue is similar in the unscaled tune. Anyway, I'm modifying the Wall Impact Factor vs airflow table and it's getting better (larger numbers in low airflow areas and blend to stock numbers in higher airflow areas). Question is how do I tell what part of that table the ECU is using? During a throttle transient you have a range of airflows. Also, I would like a way in the scanner to tell if the ECU is in steady state or transient mode and I can't figure out what to log to tell. Does fuel trim cell change? The closed loop flag? There is also a fuel system status, do any of these indicate the ECU is in transient fuel mode?

Blind squirrel method of looking at the log as guessing which airflow it's using is getting me closer. But as I get close, I will need a better, more scientific method. Thanks.

[Pekka_Perkeles]

Well, I would forget transient for a while and try to get VE where it should be to get rid of lean spikes.

But if that won't help, I don't know how to get transient fueling correct, sorry.

[kingtal0n]

Is this on a 411 computer?

People will need to see the tune file to establish what menus, variables you have access to. Every file has its own specific selection of available adjustment parameters.

[pknowles]

Tune and log attached. VE is perfect (at least the regions I hit up to about 9psi) and MAF has been tuned. It runs great, just trying to get rid of these lean spikes. Note, I'm doing this tuning on low boost ~5psi with E85 in the tank so I can't hurt anything. There is a small lean spike on acceleration at 14.2 seconds and a big lean spike at 24.2 seconds during decel. At 14.2 seconds you can see it goes a hair rich just before it goes lean. Whatever it's doing on transients I want it to do it longer. Thanks.

2020-11-14V2_Scaled_ImpactFactor_part.hpl

2020-11-14V2_FlexFuel_2BAR_4L80E_injectors52p3psi_LS7MAF_scaled66p7_TransFuel.hpt

Yes this is on a 411 and tune is scaled by 66.7%.

[5FDP]

The injectors basically shut off on decel, that is normal to go lean if De-acceleration fuel cut off is active. All of these engines will do that, it saves fuel and helps with engine braking.

[pknowles]

The injectors basically shut off on decel, that is normal to go lean if De-acceleration fuel cut off is active. All of these engines will do that, it saves fuel and helps with engine braking.

Yes, but as I'm backing off it goes lean (peak at 24.2 seconds), then comes back close to stoic, then goes into DFCO. I'll disable DFCO tomorrow and try again.

[pknowles]

Not DCFO. I turned off DFCO and relogged. See tipin and tipout files. You can see it goes a little rich than a little lean on tip in before going into PE. Tip out shows a huge lean spike. Not sure what to do other than keep playing with transient fueling.

2020-11-16_Scaled_ImpactFactor_tipin.hpl

2020-11-16_Scaled_ImpactFactor_tipout.hpl

[murfie]

BOV acting like a giant leak fooling the MAF sensor. You see the MAF signal in hertz reflect what the WB reports, the actual MAF airflow and dynamic smooth it out.

MAF is best for steady state, MAP is best for dynamic airflow. Work your RPM(Hi) and MAP(Lo) thresholds to make high RPM /low MAP conditions not steady state to have it follow MAP more than MAF, which is not accurate when BOV opens, but the MAP still will be.

[Ace4045]

I would think a speed density tune would help you out a lot more as you have better control over fueling especially with boost.

[pknowles]

I would think a speed density tune would help you out a lot more as you have better control over fueling especially with boost.

Speed density does solve a lot of these problems. I flashed a speed density tune back in my truck today. Throttle response and smoothness have taken a negative hit. I'll drive a around for a few days to see if speed density gets better.

[Lakegoat]

Your engine selection says 6L but the cylinder volume is wrong. Should be 0.70819. Under fuel---are you running a boost referenced return fuel system? The ifr says you are , the offset vac table says different. Speed density will not get better as you drive, gotta retune. I would change the boost enrichment to 105kpa to 107 instead of 120.

[pknowles]

It's a scaled tune, scaled by 66.7%, so ~.75L goes to ~.50L in scaled tune. Yes boost referenced. Didn't catch the offset vac table, thanks!

Updated the offset vac table today and went for a drive. My CLSD tune is much smoother than before. I think I'm giving up on transients n the MAF tune now that CLSD runs smooth. Thanks.

[kingtal0n]

I thought 411 supports 200lb injectors, why did you scale? What size injectors?

I have no issue running 100lb injectors with my 411, unscaled, flex fuel, 800hp.

Alot of your issues may simply because of the scale. There are unknown number of maps which interconnect that depend on injector size value.

Always ditch the maf if you are not a maf expert.

[pknowles]

I thought 411 supports 200lb injectors, why did you scale? What size injectors?

I have no issue running 100lb injectors with my 411, unscaled, flex fuel, 800hp.

Alot of your issues may simply because of the scale. There are unknown number of maps which interconnect that depend on injector size value.

Always ditch the maf if you are not a maf expert.

I scaled due to the 4063 lb/h limit on the MAF table. Unscaled I would hit the 4063 limit around 10psi of boost pressure. I'm using an LS3/LS7 MAF in a 4" tube. The injectors are 1000cc/min from Fuel Injector Clinic, flow rates adjusted for my fuel pressure.

Honestly, the scaled MAF tune has run excellent except for quick throttle transients. I had to bring the High RPM disable (MAF only above this) down to 1400rpm because the predictive coefficients that we don't have access too are way off for FI. However, with MAF only, the throttle transients are garbage. Fix one problem and create another.

Now that Lakegoat found my injector offset table mistake (huge thanks) and CLSD is running well, I'm going CLSD so I don't have to worry about scaling and transients. Already reworking idle tuning in CLSD.