5.3L Tuning -- MAF Removed and Runs Better?

[Fast4.7]

I've noticed that not all the a/f walk out is due to IAT because sometimes when heat soaked I can adjust my IAT back to ambient and I am still lean on the wideband.


I think some of it is due to the voltage drop, my alternator output drops maybe 0.5v during a heat soak situation because the exhaust runs nearby the alt.
another issue is heating of the fuel system and injectors. Injector solenoids fire more slowly the hotter they get. Hotter fuel is less dense. Taken together the same pulse duty is less fuel over time during a heat soaking (I am running a DEAD HEAD for simplicity @ 600rwhp), compounded with reduced voltage, ofc I tried adding comp to the injector delay during reduced voltage but that never seems to cover the spread. So now I just keep turning the IAT until I see what I like.

Mine is the opposite direction. Mine is definitely all IAT temperature driven and only in speed density. Mine is lean with lower IATs and rich with higher IATs. When the IATs are cold in the 20-50*F range it will run +6% or more fuel trims. When the IATs climb to around 70-100F which is where the IATs sit most of the year while driving down the road the fueling is pretty much spot on. When the IATs get up over 120F and head toward 170F the fuel trims will drop to -6 to as much as -10%. The problem goes away completely if I switch to MAF only. I have run the engine with the alternator disconnected and a steady voltage applied to the system with an old analog battery charger that holds a steady voltage on the system. The drift stays the same. It is reproducible on every cold start and warmup, with the hood shut. Run the engine with the hood open and the fueling drift never occurs.

[Tunercharged]

Mine is the opposite direction. Mine is definitely all IAT temperature driven and only in speed density. Mine is lean with lower IATs and rich with higher IATs. When the IATs are cold in the 20-50*F range it will run +6% or more fuel trims. When the IATs climb to around 70-100F which is where the IATs sit most of the year while driving down the road the fueling is pretty much spot on. When the IATs get up over 120F and head toward 170F the fuel trims will drop to -6 to as much as -10%. The problem goes away completely if I switch to MAF only. I have run the engine with the alternator disconnected and a steady voltage applied to the system with an old analog battery charger that holds a steady voltage on the system. The drift stays the same. It is reproducible on every cold start and warmup, with the hood shut. Run the engine with the hood open and the fueling drift never occurs.

So it would seem that maybe some insulation around the wire and IAT sensor or maybe some kind of plumbed in fresh air dump on the sensor would solve the problem? Personally I’m enjoying using the MAF on my truck even with KN filter. I set up ram air feed from front of truck under aftermarket bumper to bottom of sealed factory filter box, so no heat soak on IAT.

[Fast4.7]

So it would seem that maybe some insulation around the wire and IAT sensor or maybe some kind of plumbed in fresh air dump on the sensor would solve the problem? Personally I?m enjoying using the MAF on my truck even with KN filter. I set up ram air feed from front of truck under aftermarket bumper to bottom of sealed factory filter box, so no heat soak on IAT.

It is air that enters the air box that is that hot. The air going into the box is not ducted out of the engine compartment and I have not figured out a way to do it either other than cutting a hole in the hood. Not really a fan of that approach either as water does not compress. Easiest fix for me is to just keep the MAF in place, it works and works very well. Better than speed density ever thought about working which is been my whole point all along. The MAF self corrects for temperature, pressure and thus density by directly measuring the airflow across the hot wire element.

[kingtal0n]

The HPtuners ECU airflow model is getting leaner with higher IAT. That your's is backwards makes me think maybe
A. Something is corrupted in the file or ECU
B. Something in the file you have not noticed is causing the swing such as the timing vs IAT table or perhaps the charge density model (have you disabled CTS density model?)
C. MAP sensor is bad, causing drift during temp changes
D. Fuel pressure is wandering, due to temp of regulator?

I would
A. Try a different ECU and start from scratch on a new file
B. Check every setting in the file 1 by 1
C. Change the map
D. Watch fuel pressure during swings
and
E. Install a variable resistor to confirm the relationship is with the IAT alone

I assume you are open loop and wideband is installed properly with no exhaust leaking as well. 1 wideband on all 8 cyls? If its 4 cyl per wideband sensor then maybe you can check the other side, perhaps an issue with a single injector is causing this on one side.

[Fast4.7]

The HPtuners ECU airflow model is getting leaner with higher IAT. That your's is backwards makes me think maybe
A. Something is corrupted in the file or ECU
B. Something in the file you have not noticed is causing the swing such as the timing vs IAT table or perhaps the charge density model (have you disabled CTS density model?)
C. MAP sensor is bad, causing drift during temp changes
D. Fuel pressure is wandering, due to temp of regulator?

I would
A. Try a different ECU and start from scratch on a new file
B. Check every setting in the file 1 by 1
C. Change the map
D. Watch fuel pressure during swings
and
E. Install a variable resistor to confirm the relationship is with the IAT alone

I assume you are open loop and wideband is installed properly with no exhaust leaking as well. 1 wideband on all 8 cyls? If its 4 cyl per wideband sensor then maybe you can check the other side, perhaps an issue with a single injector is causing this on one side.

A.) Does it with both the P01 0411 and the 2005 P59
B.) It has less swing with the CTS model disabled, tried that a long time ago. Also tried with the CTS model enabled and the settings for 3 different year models of Express vans as well as the Mexican L31. All 4 temperature models are worse than with the CTS model disabled.
C.) MAP has been changed and the MAP reading is stable when the engine is up to temperature and stays the same as the IAT rises.
D.) Fuel pressure is rock steady. Two different regulators as well.
E.) I went from a L31 truck intake to a L31 marine manifold and the problem is the same.
F.) I have blocked off the EVAP purge solenoid just to be double sure the purge system is not active.
G.) I have not used a variable resistor but I have substituted a fixed resistor that gave a 100F IAT reading and the fueling is rock steady. It is absolutely IAT alone doing it.
H.) The fueling drift has also existed with two different IATs and CTS sensors. First had the OEM divorced L31 IAT and now has a LS7 cartridge MAF.
I.) This has done the same thing with two different engines as well.

I am in closed loop and although ALL of my L31s have had a small split in the fuel trims, LH bank richer than the RH bank by 3-4%, both banks drift the same amount and follow the same trend. I even made histograms for both banks and compared them to the average. Both have the same trend with the slight split. To a lesser extent my 8.1L Tahoe does the same exact thing. It has the same drift in speed density only just not as much drift. The 8.1L does not have nearly as much IAT swing once it is warm because of the sealed fender intake.

The weird part is I can enable the MAF and the air/fuel swing is almost non existent.

[2000Phoenix]

Totally agree. Iat temp swings are brutal in sd and there is no steady state that I could find so i let the narrow bands do the work. I still wonder how people running olsd with maf disabled as it keeps it in a steady state much easier. My Dyno guy said there is a secret that I will have to figure out on my own.

[kingtal0n]

Well anywhere from 15.2 to 16.5:1 is desirable for idle/cruise. I just let it walk around however it wants, makes no difference. It will usually sit on 15.2 where I tuned it unless the traffic in the sun heat soaks it after 40 minutes, it starts to get into the 16's. The swing does not influence or affect any driving a/f ratios, I never have any wandering for cruise, part throttle, wot, etc... its only at idle I notice it walk around. So I let it. If I feel like it I just dial the IAT around with my 1000Ohm Variable resistor. Every 500Ohms adds about 12*F of cold to the iat. And the other benefit is there is a table which does IAT vs Timing so even when the engine is not heat soaked I can add timing in real time (and fuel at WOT) by adjusting the variable resistor. Its all about control, if you can control the a/f and timing into optimal ranges, then that is all that matters.

[smokeshow]

I will add to something nobody talks about. SD has a fueling drift. I am tuning here in Texas where it can be 28F on a cold start and a few hours later 75F. I have tried adjusting the IAT contribution numerous times as it is mostly related to IAT. I tried the stock values for my engine and they were way off. I used newer values from the same engine in a GMT800 truck. I tried newer values out of the same chassis with a 6.0L, still a large error that is entirely caused by the IAT swings. Finally turned of Complex Air Temp modeling that uses only the IAT and does not try to model manifold temp. That made the fueling as tight as it has been, but there is still a ~10% fueling swing in SD between 28F and 170F IAT. When it is 75F outside my factory air box has IATs ranging between 80F and 170F depending on speed and load. I have considered moving the IAT to the Bosch T-Map in the manifold plenum in an attempt to calm sone of that swing even more. With a cast iron lower intake and aluminum upper lid, I feel the IAT will be more stable and thus less of a fueling swing after warmup. With the MAF enabled the fueling does not experience these dramatic swings.

The other thing nobody mentions is that GM calibrated the line pressures and torque based stuff around a properly functioning and calibrated MAF.

I mean, even cone stock stuff ends up walking around lol. I logged my 2016 V the other day and fuel trims were like 20% out....car is bone stock. Probably good to manage expectations. That said, I would not opt for any metal in between the outside air and the combustion chamber lol. One of the most challenging speed density setups I've worked with was an MP112 CTSV with a wild IAT sensor location and a ridiculous amount of hot metal in the intake airflow path due to the blower. It was definitely beyond the capability of the OEM software to manage.

On paper, the SD fueling drift is manageable with the complex air temp model, given a reasonably tame combination. Start getting wild with the cam on a gen3 though and the model becomes less capable due to the internal EGR. It wasn't until gen4 that GM incorporated EGR compensation in the charge temp model.

[Fast4.7]

I mean, even cone stock stuff ends up walking around lol. I logged my 2016 V the other day and fuel trims were like 20% out....car is bone stock. Probably good to manage expectations. That said, I would not opt for any metal in between the outside air and the combustion chamber lol. One of the most challenging speed density setups I've worked with was an MP112 CTSV with a wild IAT sensor location and a ridiculous amount of hot metal in the intake airflow path due to the blower. It was definitely beyond the capability of the OEM software to manage.

On paper, the SD fueling drift is manageable with the complex air temp model, given a reasonably tame combination. Start getting wild with the cam on a gen3 though and the model becomes less capable due to the internal EGR. It wasn't until gen4 that GM incorporated EGR compensation in the charge temp model.

Speed Density is less accurate, and nothing is going to change that fact. The MAF is actually measuring the air charge volume change with temperature, pressure and density. EGR does not affect the air/fuel ratio. The MAF measures the intake charge air volume being pulled across the MAF even with the corresponding density change from the manifold heating and the PCM injects the necessary fuel.

Personally I would run MAF only before I ran Speed Density only. When I make a startup tune it is MAF only until I get some data logging done. I actually rough in my VE tables by calculating VE from the resulting data. This method is far quicker and easier, especially on a vehicle with the stock MAF ducting and air box.

[smokeshow]

Speed Density is less accurate, and nothing is going to change that fact. The MAF is actually measuring the air charge volume change with temperature, pressure and density. EGR does not affect the air/fuel ratio. The MAF measures the intake charge air volume being pulled across the MAF even with the corresponding density change from the manifold heating and the PCM injects the necessary fuel.

Personally I would run MAF only before I ran Speed Density only. When I make a startup tune it is MAF only until I get some data logging done. I actually rough in my VE tables by calculating VE from the resulting data. This method is far quicker and easier, especially on a vehicle with the stock MAF ducting and air box.

Bit of a blanket statement.. Try running a MAF in a 6" intake tube and you'll see what I mean. When the MAF is subject to reversion effects without the means to filter it out, again...not a great way to measure airflow. As with everything, there is a compromise. A MAF may be accurate under a wide range of scenarios, but it is still several feet away from the intake valve. That doesn't come without disadvantages. I personally prefer the SD/MAF combination in any application that can manage it.