Off the line idle to WOT throttle bog finally cured...

[BBA]

Help us all out here... If you can show us something based on an actual scan, it may make sense. Otherwise....

Satisfied?

[rrmccabe]

Not false, those are the range of cells where negative timing caused bog. I changed them to positive timing and no more bog and no more dips in timing when I nail it from a stop.

Just because your older computer does not have a fast enough data bus speed to show it on a scanner, it's still doing the same thing mine did. Bump up those values and the idle to WOT bog disapears.

I am not arguing your results. I just think something is out of wack.

A N/A bolton LS-2 does not flow 1.04 g/cyl. Especially at 800 rpm. The Maf is freaking out or something.

[BBA]

Exactly, it freaks out on the in-rush of air when you flash open the throttle from a high vacuum idle to WOT. That intake has a lot of volume under vacuum that fills up with air pretty darn quickly and all that air comes in right through the MAF sensor. The sensor basically tells the PCM it is under (an unrealistic) high air flow condition and the PCM cuts timing because of the corresponding timing table values.

Why is that so hard to understand?

I think your confusion is coming from the fact you are more or less only thinking along the terms of near steady state airflow at various RPMs.

This condition is a dynamic pressure fluid flow condition that has really nothing to do with how much air the cylinders are actually taking in, just how much air is flowing over the MAF until the manifold vacuum equalizes to the incoming air pressure. After the pressures equalize, the airflow slows to normal parameters. This is where understanding basic transient fluid flow and pressure really helps get you out of the 'how I thought it was supposed to work' mindset.

[LazMan]

It is true. I tested it yesterday on my 2006 GTO and while my resolution doesnt compare to the e38 computer, I got two hits down low on rpm at 'high load' ...

I used the stock 2008 Corvette 7.0L tune as a guide to change all my negative timings last week and I can feel the difference too when I stomp on it. Its MUCH more responsive.

I didnt go from negative to zero, I went to 1, 2, 3, then smoothing to normal as i go up the columns, again using the 7.0L as a guide.

The new 6.2L 08's don't have negative timing there either.

PS: Do the same amount of adjustment on your low-octane table afterwards.

[BBA]

Something seems funny. Those .80 and higher readings must be false. No way you are seeing flow of over 1.0???

I just noticed something RMCCABE, your flow histograms are completley differnt than mine because YOU are not using a stock MAF Sensor AND YOU have adjusted the hell out of your MAF tables.

That may be why you are having a hard time relating, your setup is totally different than any stock TBSS, of course you will see different flow numbers.

[rrmccabe]

Hey BBA, could be. I really dont know. Just debating with you.

And BTW, my above screenshot was a stock MAF. As you know I have ran multiple intakes, canned tunes, and self tunes for the shootout test. I am using a ADM intake now. But the above happened to be a Vector intake.

[BBA]

Hey BBA, could be. I really dont know. Just debating with you.

And BTW, my above screenshot was a stock MAF. As you know I have ran multiple intakes, canned tunes, and self tunes for the shootout test. I am using a ADM intake now. But the above happened to be a Vector intake.

Funny you say that, because I was thinking an intake with less internal volume would have less of this problem. Maybe like a single plane like the GM PP intake, with FI bosses and a 4 barrel throttle body under a 90º elbow to the MAF and filter.

I't think the closer we can get the throttle body to the intake ports the less throttle lag we will have, and I have no problems with the torque made by a single plane intake, I've ran them for years on SBC's and you just can't knock them.

[LazMan]

But, in SBC's you meter at an inch (or so) above the throttle blade ... doesnt the MAF meter YARDS away from the throttle blade? I always thought that was the larger part of the throttle response delay with MAF...and why SD doesnt have it (as the computer "guesses" .. bad word, i know ... "educatedly guesses" at the airflow)

[BBA]

I think it's more related to intake volume between the throttle blade and the cylinders. A higher volume will cause a larger flow transient when opening the throttle, and FI MAF cars typically have huge intake volumes due to long runners tuned for torque at specific RPM's.

The distance the MAF is away from the throttle body will effect the response lag of the transient airflow reading but not the actual value of the reading itself unless the volume of the intake to MAF duct is super huge, in which case a pressure oscillation will develope, which can cause whacky readings.

[Zfiddy1]

All I can say is from the histograms, I see mine hitting the high flow low rpm cells every time I punch it from a stop. You just need to look to see it, of course in your case with a high stall, it will be so quick you might not even resolve it, but with my TBSS and the super high frame rate the new PCM has with HPT, it's easily apparent.

You don't believe me...try it yourself. I don't get paid to argue. Enough said.


(Then again, I don't get paid to do this anyway, it's a hobby for my pleasure.)

I hit a few down there too, I am buying the argument. No harm in setting them to zero. I showed +2 degrees in my log when I had them set to zeros.

[BBA]

I hit a few down there too, I am buying the argument. No harm in setting them to zero. I showed +2 degrees in my log when I had them set to zeros.

Well, tell us about it? Does yours pull hard and smooth from a dead idle to WOT stab?

I'm liking the fact mine finally gets up and goes when I want it to, I have almost had a few close calls pulling into traffic before I did this to mine, now there is no worries about the power, it's there when I want it to be and makes me feel less worried when letting the wife drive the SS.

[LazMan]

I think it's more related to intake volume between the throttle blade and the cylinders. A higher volume will cause a larger flow transient when opening the throttle, and FI MAF cars typically have huge intake volumes due to long runners tuned for torque at specific RPM's.

The distance the MAF is away from the throttle body will effect the response lag of the transient airflow reading but not the actual value of the reading itself unless the volume of the intake to MAF duct is super huge, in which case a pressure oscillation will develope, which can cause whacky readings.

Makes sense that the intake volume would be an issue ... but, I've always thought that the MAF being far-away from the throttle-body adds to the 'inaccuracies' in metering.

[LazMan]

Additionally GM was indeed brilliant in using SD + MAF below 4000 (or 3600) RPM ... BRILLIANT!

[n77nxc]

Has anyone tried this on a vette?

[psrumors]

I have been unable to hit the cells in question whether FI or NA. I have tried this with the -timing in place and removed and never could tell a difference. Though I have never had any bogging issues.

BBA, is it possible something else in your tune has enabled this to happen?

[Sneakyws6]

I have a 2008 TBSS 2wd and have been doing some reading and messing around with mainly my tranny calibration. I just modfied a new calibration and will try this on the way into work tomorrow and see how it works but I completely understand and agree with what BBA is stating with the intial rush of air over the MAF causing it to misread the intial airflow until the intake airflow stabilizes in the intake tract.

[LT1GMC]

I was talking with a Delphi engineer about sluggish off idle response on my TBSS, and he mentioned a "silly" program to desensitize the throttle response on electronic throttles, its a routine that compares rate of throttle opening to reduce jerkiness for less than accurate throttle applications. (non-perf drivers). Its also to protect from a shorted throttle sensor. Maybe this is how they do it, reduce spark at too quick sudden inrush of airflow. Anyone else know anything about this?

[WarWagon]

I was talking with a Delphi engineer about sluggish off idle response on my TBSS, and he mentioned a "silly" program to desensitize the throttle response on electronic throttles, its a routine that compares rate of throttle opening to reduce jerkiness for less than accurate throttle applications. (non-perf drivers). Its also to protect from a shorted throttle sensor. Maybe this is how they do it, reduce spark at too quick sudden inrush of airflow. Anyone else know anything about this?

This 'silly program' is probably why throttle by wire feels so numb in most vehicles.

But going WOT like BBA has with the timing can induce a single audible knock. At least it does in mine.

[BBA]

Wow...resurrected.

warwagon, must just be you...you sure it's you motor knocking and not yer head knocking against the head rest?

[WarWagon]

Wow...resurrected.

warwagon, must just be you...you sure it's you motor knocking and not yer head knocking against the head rest?

My IAT's suck! And then I have 91 tops for gas out here.

Yes, head hits head rest and all other loose contents hit the back hatch! It does do what is advertised!

But there is a single audible ping and 4 Degrees of KR showing up in the scanner. Not that I think a single ping is going to hurt anything...

Update w/ logs
Engine Cold is not as bad as warmed up. So here is a good reason to get a 160 stat.

Looks like the fuel is not following the MAF spike fast enough in log 2 it goes from 2% to 8% after the spike?