Descreened MAF batter than screened?

[GNXClone]

A little history...

I used to run my twin turbo GTO on my self tuned, 2.5 BAR OS, speed density tune. This tune was great. I didn't touch it in nearly 2-1/2 years of daily driving. Dynoed at 554 RWHP/572 FTLB. Since I was running it as SD only, I 'gutted' the MAF. I took the screen out and drilled a hole in the center airfoil for my meth injection nozzle, I like the stealth look . I left the circuitry intact and logged from it still, but the data was not used for any fueling calculations.

Recently, I've changed my engine combination (cam, heads, compression and injectors). I've disconnected the meth injection and reinstalled an untouched, unmolested MAF sensor. I've re-enabled the MAF for fueling calculations to make tuning easier until I get the VE tables tuned.

Now I'm seeing an unexpected lean condition under boost when at part throttle versus full throttle. When at part throttle, with PE enabled, as the boost rises, the MAF doesn't appear to follow along properly.

With the old setup, the MAF I descreened and hacked up did follow the boost, in that, as the boost rose, so did the Hz output of the MAF.

Since my fueling is now based on the MAF, I suspect this is the cause of a lean condition under boost. The lean AFR curve appears to follow the boost curve identically. During this time, the MAF stays pretty flat, relative to the boost curve.

I have a screen shot of two logs. On the left is the new combo, MAF based fueling, with the lean condition. On the right is a log I took two years ago with the SD setup using the hacked up MAF. Both log snapshots are during a part throttle pull.

You can see in the OLD log that the MAF output follows the boost curve. But the NEW one does not.

If I got WOT, this doesn't happen. At WOT, the boost and MAF curves follow one another nicely.

Any ideas what's going on? I would have thought an untouched stock MAF would be more accurate than one which has been gutted.

Guess it's time to get those VE tables dialed in and get away from the MAF.

[GNXClone]

Attached logs used in screenshot and cfg.

Gutted MAF:
tune_12_nice_trans!.hpl reference frame 2118

Untouched MAF:
fw2.hpl reference frame 1160

[IDRIVEAG8GT]

Is your PE set the same across the board? With my G8, at about 1/2 throttle I see 2-3psi boost, and about a 13:1 AFR, then the farther the pedal is pressed, the richer it gets, despite the rising boost levels. Transient fueling can adjust things like that.

You can use bluegoat06's part throttle MAF tuning guide to ease the process of getting the MAF dialed in. Then you're free to basically change the larger Hz cells in the MAF to whatever gives you your desired AFR.

[GNXClone]

Is your PE set the same across the board?

Yes. 1.35 in all cells of "EQ Ratio vs RPM" and "EQ Ratio vs MAP" (in Boost Enrichment). This should command 10.88:1. I know this is overly rich, that's intentional at this stage.

You can use bluegoat06's part throttle MAF tuning guide to ease the process of getting the MAF dialed in.

I did not know there was a part throttle MAF tuning guide or that part throttle even made a difference. Interesting...

Thanks!

[MMGT1]

I would attack that VE and part throttle tuning with the screen in place. From what Ive seen over the years, running with a de-screened MAF never ends well. The car will run fine sometimes for some reason, but in the end it just messes with the part throttle and idle too much. There is just far too much turbulance over the sensor without it. Are you running a card style MAF or a three wire MAF?

[MMGT1]

Another thing you can do with a head and cam car is to run in PE mode at idle and part throttle. Just aim for your 14.7 to 1 or whatever stoich is in your PCM. That way the lope of the cam will not send your sensors into a fit with the overlap and exhaust gasses that get pulled back into the combustion chamber at idle especially. I would at least run PE at idle and use your WB to set it up right. I would also pick a point around 1200 to 1400 RPM to have the PE shut down and then use MAF calcs to 7500Hz, then back into PE. I hope this is making sense....lol