2006GTO tip in hesitation

[dynoguy]

Hey guys, cant get this one figured out. Vehicle runs flawless other than an occasional snort through the intake.Trims are perfect. Fuel press perfect.Its a 6.0L with a 224/234 cam, LS3 heads and intake,LS3 injectors, Long tubes, etc...Any thoughts???

[camarochevy1970]

Does it do it if you go either maf only or ve only?

[Elton]

Your VE, PE and spark tables all look a little messy, could be smoother..

[dynoguy]

thanks guys, its going back on the dyno now to see if i can find it. I will keep you posted....

[dynoguy]

I failed the MAF and did the complete VE tune, never had bothered to do that. It was in fact way off, but hesitation remains..I notice it mostly when coming down from 50MPH to make a right turn at a light, right when you get back in the throttle, pop, then off it goes....

[camarochevy1970]

Do you see large timing jumps in your log when that occurs?

[dynoguy]

found burst retard was acting up, fixed that but still snorts occasionally

[DSteck]

MAF curve needs work, and if you're going to rely on the MAF and tune it properly, you need to put the car in MAF only mode. Beyond that, VE needs to be tuned independently as well. I think you're just got an airflow model problem.

[dynoguy]

DSteck, what do you see wrong with the MAF curve??? also, how do I put it in MAF only mode??? done quite a few of these things, but by no means an expert...I thought if I failed the MAF i could could do the VE table, the re-enable the MAF...Any help is appreciated...Mark......I attached the most recent tune after I did the VE table on the dyno last week

[madvette08]

Go to Engine > Airflow > Dynamic Airflow. Set the High RPM Disable and re-enable to 0. That will put you MAF only mode.

[dynoguy]

And then what???go through and re-tune the MAF freq table ???? then re- enable VE???? thanks

[Frost]

The stumble in the log is clearly a lean stumble; both 02s hit the floor. The MAF curve is low in 5.5-7KhZ area. Aside from that, get PE in sooner. Set enrichment to 2.0 and eliminate the delay. They may or may not be active in your cal, but it's just part of being thorough. The TPS trigger can move down a bit as well.

[IDRIVEAG8GT]

DSteck's method is setting RPM enable to 2, and disable to 1, at least that's how he taught me. The stumble that I used to have in my G8 was from improper MAF tuning. You'll probably see it if you rapidly touch the gas and let off, it'll fall dead for a second because of your MAF (Lean) as Frost said, so you're going to want to add to your MAF table(s). Leaving VE out of the equation for now, keep an eye on those fuel trims, and if you can, hold each Hz level via RPM with a warm engine, take a note, reset the trims, then move to the next Hz section by raising the RPM slightly so you can see what each is doing from idle Hz and 5 cells afterwards. This should cover enough area on the line to start to show you how aggressive your curve is going to end up. It makes it easy for me. Good luck.

Edit: Just glanced at the Log, Do you know what the AFR is? And by the looks of it I'd junk that MAF tune and start over again. Those #'s are all over the place. It's kind of cheating but take a Stock MAF tune out of say an LS3 Vette in the repository, run it in the car, figure out how far off it is in one cell, and add or subtract the percentage it's off to the entire table and that should actually stick you pretty close. It's not just a huge cam we're talking about here, and from there you should be able to tweak it till you get it right.

[dynoguy]

Thanks to you all.. I richenned the MAF table from 5ooo-7000, enabled PE sooner and changed the erichment to 2.0.....No mas hesitation....I have it in MAF only right now, should i re-enable the VE????? Again, thanks to all, dont know why this thing beat me up for awhile...It ran so darn well other than the once in awhile stumble....

[bluegoat06]

You can leave her MAF only if you want, or correct VE and have both mods enabled.

If you're going to re-enable the VE, disable the MAF, and correct the VE. Always remember that both mods should be tuned independently from each other. if tuning MAF, disable VE and focus on the MAF, if tuning VE, disable MAF and focus on VE. then at the end, you can have them both enabled.