98 Suburban 7.4

[SiriusC1024]

This part goes pretty quickly.

MAF curve updated. Run it again. Just a reminder clear your fuel trims.

The MAF you're using will work fine since you've kept up on it.

The thing I was wondering was if your intake was restricting anything. It is. Ignition on/Engine off shows 94kpa. That's about 2000ft elevation. One WOT pull I looked at in a previous log showed 89kpa. So, your intake system can't keep up with the demands of the engine. First thing to check would be that the throttle blade is opened fully with the pedal all the way down. Make sure the cable is tight with the throttle closed. I remember the 90's Ford Explorers did about 70% throttle at 100% pedal. After that it's intake piping. Sometime vehicles have a restriction in the airbox to quiet intake noise. It's a trumpet shaped piece that is the intake for the airbox itself. Look around and see what you can find.

Nice thing is the SD side won't be affected at all. MAF probably won't, either. Depends on the restriction and how it's removed.

Post a pic of your engine bay and the intake stuff please. Upload and click insert inline.

[Spareparts]

Yes i am resetting the LTFT each time
This time it feels like it is running a little rougher than before.
Man you would think living out in the country more or less it would be easier to find places to get good WOT upper RPM pulls but traffic and houses everyplace it seems like.
Here is another from start to finish.

SiriusMAFLog2.hpl

[Spareparts]

Just seen your edit above. Ill post a pic but yes i have read the Vortec intake runs outta air around 4200 RPM
These engines are made for low rpm torque and towing heavy loads and not high rpm like a true high revving engine with a better flowing intake.
I dont do much towing and just a little stoplight racing. I sure don't always win but maybe 50% i do and the surprise from people at how well an old 98 suburban can run is great!
Anyway ill check it out and post a few pics here soon.

OHYA i also live at 2000 feet elevation.

[Spareparts]

Throttle is opening all the way. The air filter is only a few months old.
There are no restrictions in the intake tubing as a guy would think to look for. Once it makes a turn out of the filter box it's almost a straight shot to the throttle body.
The big thing that says Vortec is a resonator box for sound dampening.
Enginebay1.jpg
Engine bay2.jpg
Engine bay3.jpg

[SiriusC1024]

Here's MAF 3.

It's not the intake running out of breath. That has to do with runner shape and volume. The intake itself is seeing the drop in pressure, so it's feeding the engine alright. The plenum should measure atmospheric pressure at WOT.

This is the type of thing I'm talking about. Is your airbox restricting things like this one? I know wrong year, but good example.
airbox.jpg

[Spareparts]

Yeah, Mine has nothing restricting it unless it's in the finder where you can't see it. Air is taken from the front core support area and ducted to the air box and i dont believe there are any retractors in it from what i have seen.
This tune was much better than the last but still a little rough and i think i can feel it just normal driving holding a steady throttle.

SiriusMAFLog3.hpl

IMG_20230706_171932224_HDR.jpg

[SiriusC1024]

Fuel trims are pretty tight. I think what you may be feeling is KR. That's next. Start logging Cylinder Airmass (g) so the spark tables work right in the log.

All the airflow should be done with this tune. Something is causing a restriction. Assuming the opening to the fender area isn't obstructed, next idea would be throttle body. A little port work looks like it could do some good. If you ever decide to go bigger the nice thing is that both airflow models will compensate, but it's likely the idle settings will need a little tweaking (92mm and larger. 80mm BBK will work fine). If the intake tubing itself is changed then MAF will have to be re-tuned.

PE DFCO re-enabled. PE adjusted. WOT shift down to 4900 rpm. Fuel cutoff 5000rpm.

[Spareparts]

It looks like your telling me to adjust something on my log, but you're way over my head at the moment.
I understand Cylinder airmass is a combination of MAF and VE. From reading.

In my log i have the MAF set to G/Sec. Do i need a graph of the G/Sec also?

My cylinders measure 4.280 bore, 4in stroke, flat top pistons with .3cc valve relief, .015 deck hight. Heads are 100cc Vortec and head gasket measures .022 compressed gasket thickness.

I did increase spark by 1 degree on the entire table under Engine, spark, base and also under Engine, Spark, Idle spark advance in the original tune i posted.
I had planned on going back and taking 1 degree out on each cell showing KR. Probably the wrong way to do it but seemed reasonable to me at the time.

LogPic.jpg

[SiriusC1024]

There's a channel called Cylinder Airmass (g). This informs the Y-axis of the spark advance and retard histograms.
cylinder airmass.png

Wait nvm. The tune has the spark tables as MAP vs RPM. You're fine. I'm used to LS format. Proceed.

[Spareparts]

Ah, ok. I'll get a log posted tomorrow morning (ish) from cold start.

[Spareparts]

Trying to add Cylinder Airmass but it is grayed out and will not let me keep it.
As soon as i connect to vehicle it goes away. Researching now to see if not supported by my ecu or what im doing wrong.

[Spareparts]

Well from what i read Cylinder Airmass is a parameter that my ecu does not support.

[Spareparts]

Ah dang. Just seen your edit. Ill go get a log.

[Spareparts]

Truck seems to be running pretty good with this tune Still slighty rough at idle. WOT pulls are solid and sits ya back in the seat. Decent for what it is. Definite improvement so far.

SiriusMAFLog_4.hpl

[SiriusC1024]

Fuel trims are now being skewed by STFT Open Loop Enabled. Don't pay attention to them.

Rough idle seems to happen only on warmup. Adjusted OL fueling.

Spark reduced where knock occurs.

Run the tune. Point out anything else you need adjusted.

[Spareparts]

Thanks for all the effort you have put in man it IS much appreciated
Idle still a little rough but could it be the LTFT needs to learn as im always resetting it and a new tune every time?
Seat of the pants dyno says it is running better than ever after the rebuild. The engine is now getting the 6k lb truck moving pretty good!
If you're happy with it at this point i think the best thing to do is drive it a few days and let me get a feel for all the changes. Whats your opinion?

SiriusLog Full-1.hpl

[SiriusC1024]

That sounds like a good idea. Get a good feel for it.

Since you're here apply this one.

[SiriusC1024]

Hey sorry I dumbassed the RPM Near idle spark table. Here it is fixed.

[Spareparts]

Sorry, the wife been wanting to ride about so been hard to get ya a log.
Truck does not like the higher idle rpm. Feels worse almost like a dead cylinder but i dont think that is what it is.
Here is a log from your last file.

Sirius Spark Log 1.hpl

[SiriusC1024]

That's strange. That miss you're feeling is probably the ghost-cam effect that the amped spark corrections are doing.

Here. I lowered the idle down and put some deadband into the near table.

This log I did see the IAT starting to react to maintain idle. Increased based running airflow 5%.