Golf&GM

iTrader: (22)

I'm still new to this so please bear with me.

I have a bolt on 99 T/A that I'm tuning. I unplugged the MAF, copied the high octane spark table to the low octane spark table and logged LT and ST fuel trims. I got the primary VE table close, then disabled LT fuel trims and got the ST fuel trims to +-5 up to 4000 RPM.

After getting a decent log and feeling comfortable with my Primary VE table (only table adjusted thus far) I reconnected the MAF and my LTs are suddenly in the 15 to 25 range. To test I flashed the PCM back to stock and the LTs were lower.

My question is why would the MAF cause the car to run lean if all I've done is richen the primary VE table? I'll admit that my knowledge of how the MAF works is limited but this just doesn't make sense to me.

Full-Force

iTrader: (11)

Pretty sure you have to copy the primary ve to the secondary or it doesnt change anything

xBRadX

iTrader: (1)

The MAF needs to be calibrated as well. If you are using a wideband you can log all of the appropriate PIDS together and apply the same correction to the MAF table that you use for the VE table.

Which software are you using?

Golf&GM

iTrader: (22)

I'm using HPT. I have a wideband on the way but it hasn't arrived yet. I copied the Primary VE table to the secondary VE table and logged this morning on the way to work which is about a 30 min drive. Most of my LTs were pegged at 25 and the STs were in the 4-15 range. When I was running the stock tune my logs never showed it to be this lean. Is this normal? I don't get how increasing the primary VE and secondary VE tables can cause this result. I just want to make sure something else isn't going on before I start to calibrate the MAF table.

CLRD4TO

iTrader: (4)

Whats all done to the car and how much (in appx %) did you change the VE? If its stock heads, cam, intake, with exhaust and lid, it will only change by a 1-2%, if that. LS6 intake is roughly 3% change. Stock internals should be just fine with stock VE. Calibrate MAF for a CAI. You can add a couple degrees timing but otherwise nothing else really to tune for the engine.

99LS6SS

iTrader: (4)

I thought you were supposed to disable the MAF and reset the LTFTs while tuning VE?

Golf&GM

iTrader: (22)

Mods are Lid, ported TB, LS6 intake, Headers, stock catback with Aerochamber Muffler.

My VE changed much more than that. Attached is a screen shot comparison of my current VE table to stock. Running this tune in SD mode netted me STs in the -3 to 5 range with LT disabled.

I didn't disable the MAF through the tune but I did disable it by unplugging it. I then reset the LTFTs and drove it for about a 100 miles or so. I logged about a 20 min drive, adjusted the primary VE table, flashed the PCM, reset LTFTs and logged again. I did this about four or five times over the past week to get the table I have now.

The data I'm getting just doesn't seem to add up to me. It seems like I've added more fuel than I should need for a bolt on car via the VE table, but the narroband says I'm right on track. And then when I run off the MAF the car turns very lean, much leaner than it ran on the stock tune.

JustAnotherLS2

This is true. You do NOT want the MAF trying to "correct" the A/F mixture while tuning the VE table.

Golf&GM

iTrader: (22)

Sorry about the confusion there, I changed the title of the thread so hopefully it will make more sense.

turbolx

A lid alone can shift the MAF transfer by as much as 10%. Most people don't notice this since it gets masked in normal operation by being blended with the VE model.

It also very possible that your lower restriction inlet and exhaust may have changed the pumping efficiency, requiring a change to the VE surface(s). The changes to the MAF may be one direction and the VE surface(s) in the other direction. The result is usually pretty close in stock (blended) operation, but fixing one often reveals the miss in the other.

What I wouldn't expect is a hole right in the middle around 1600rpm and 75kPa. That leads me to believe that your corrections are not based on steady state data, but rather some random drive cycle where you had a lot of tip-in events in this area that were just a bit lean because the MAF was also out. The best practice here would be to run it in steady state (preferably on a load bearing dyno, fixed speed) to collect your VE correction factor data with a wideband in open loop. You may find very different corrections using this process vs what you currently have. ...then you can go back and fix the MAF transfer in a similar fashion and see how things really start working like stock again.

Golf&GM

iTrader: (22)

That does make some sense but the the terms lower restriction inlet and pumping efficiency are lost on me. I'll research those.

I believe you're right on the tip-in events. My T/A is a stock stalled auto and I haven't been manually shifting to hit the higher RPM ranges. The darker section where I've added noticable to the VE table values looks to be the point where I give it enough throttle to down shift so I can log the higher RPM and MAP ranges. The closest dyno is over an hour away and the roads where I live aren't ideal for steady throttle. I'll try to get it up on the interstate and see if I can smooth the table out.

I assume when you say collect stead state data this means to very gradually increase throttle to move from one cell to the next? To avoid a ticket I've been going in and out on throttle almost constantly to hit as many cells as possible, this is probably not the best practice.

turbolx

Exactly. The VE table is supposed to represent the filling in each cell as if you were to hold there indefinitely. (The irony is that it uses this number mostly when you jump from one to another) Constantly jumping between cells doesn't filter out all the transient fueling adders/modifier that may or may not be right just yet. Don't worry about those yet if you're tuning in steady state since they won't be active if your airflow is stable. You'll find that these adders aren't all that bad once they're referencing the right airflow numbers from the VE and MAF tables. This is one of the big errors I see today and it's easily fixed.

MUSTANGBRKR02

iTrader: (91)

If you have a WB on the way then wait and start over when it gets here. Tuning by NB and FT's can be very deceiving and leave you chasing your tail.

Golf&GM

iTrader: (22)

Would it be possible to diable the transient fueling adders/modifiers? If doing so won't cause any major issues it sounds like it would be much easier to log accurate data. With my car being an auto and having access to mainly backwoods roads it's hard to log steady state data.

UPS says that the WB is at my house now. I'm thinking that starting fresh with that would be my best bet as well.

turbolx

Turning them off would only make it worse. The real solution is to only record while you're holding a constant speed and load. In your case, it might be easier to make several smaller (steady) recordings instead on longer recording that's polluted with a bunch of transient data.

Golf&GM

iTrader: (22)

Sounds good, seemed like a shortcut fix but it was worth a shot to ask.

I will log again this weekend with a WB and a stead foot. Thank you for your help.

CLRD4TO

iTrader: (4)

Listen to turbolx, he's the man!

Go back to stock to VE tables, you are wayyy off. I just checked my baseline to cam and intake and I have a gain of 10 in roughly the areas you have as +18. Im assuming youre tuning false data. ie acceleration and DFCO, too short of datalogs, improper PID/histogram setup, etc. External bolt ons isnt going to change the volume of air the engine moves by much, thats what the cam/heads determine. Youre safer by using stock VE and calibrating MAF only. Tuning with STFT is frustrating and takes long scans to make any worthwhile data. Better off waiting for the wideband, tune for stoich, and verify your work with closed loop fuel trims. In the meantime, study the free guides on HPT forum and such, good luck.