Fire67

iTrader: (3)

Hey all, this is an LT1 application using the stock pcm. The car is described in the sig. We're trying to get the best times possible with the stock pcm before changing it out. Here's whats going on:

If I launch off the foot brake or the tranny brake, at anything over 2500rpm the car will hook, then die (by that I mean almost stall), then after what seems like a second it will come back and pull hard all the way to the finish.

If I launch from idle, it does not experience this hiccup at all and will pull clean all the way down the track.

Going either this weekend or next thursday (31st) to try something new with the methanol. I just hooked up the input from the trans brake, so that I get a reduced flow of meth whenever I'm on the TB. This makes it so that the methanol isn't ramping in when on the 'brake and does not start ramping in untill the 'brake is released. If it still hiccups, then we'll know for sure that the meth has nothing to do with it.

I just think that there's something in the tune that can help me when Im not using the 'brake. Looking for any and all suggestions, as Im a newb at tuning these things and Im at a loss as to what I should be messing with to try and smooth out the launch.

Any ideas?
Thanks in advance.

white2001s10

iTrader: (4)

The movement of the gas pedal is what controls your AE (acceleration enrichment). Leaving from idle gives you the full range so you're fine.

You need to readjust the AE tables to make up for your stalled launches.
The stumble is it going lean for a sec because it didn't get a long enough AE to cover it.

Fire67

iTrader: (3)

Ahh, that makes sense... So looking at my A/F logs, it does show it leaning out for a very short period. I guess all this happens alot faster than it seems.

So I'll likely have to have 2 different AE tables when Im finished, one for the foot brake and one for WOT on the trans brake? Or would it not matter that much if I just set it up for the trans brake and use the same setup for the foot brake as well? (Logs show 45% throttle when stalling on the foot brake)

I wish I had my laptop with me so I could look at the tables, I'd probably be more clear on the tables operation and answer my own question. But Im at work now

white2001s10

iTrader: (4)

nah, one tune should cover it all, you'll just have to extend the range into a less noticed area of the table.

Fire67

iTrader: (3)

ok, got to look at it last night. Looks fairly straight forward to me. I do believe Im clear on what your saying. I'll experiment with it this weekend. Thanks again!

Frost

iTrader: (45)

Once the VE is right (assuming you aren't trying to run a MAF) and the timing is in order, I have never had or seen a stumble. Seen plenty before the fueling was fixed, but like I said, never had to mess with "AE"...

We are talking about an F-body here right?

edcmat-l1

iTrader: (10)

Frost is right. Get the VE table dialed in, and you'll need less AE.
You may need to do a 2 bar tune. They're complicated for the LT1s, but theres info out there on how to do em, and it'll run better, you'll have less problems, it'll be more consistent, all that stuff.
BTW, the first thing I would do is make sure you have a fuel pressure gauge in it so you know if the fuel is sloshing away from the pickup.

KVU

iTrader: (1)

LT1's don't have a single AE table table. I agree with white2001s10 though. Sounds like the solution depends on how the calibration is set up.

1. You are still using the maf. It's faulty or doesn't have enough resolution in that one area. You can kind of rescale it in the launch zone. I would rather use SD though.

2. Your tps % to enable WOT is too high. I feel that it's most important to have PE come in right as the engine starts to build boost.

3. It's in SD mode and your PE compensation is in the VE (not PE) table. This means you can be at too low of a TPS @ 100+kpa. The end result is a rich bog. Don't think this is the case but it can happen.

FTR, I'm not an internet/msg board tuner. I have hands on experience and tuned over 300 vehicles, easy.

KVU

iTrader: (1)

..oh, and try to launch it (not heatsoaked) w/o the meth. That is a very quick test...

edcmat-l1

iTrader: (10)

AE, PE same thing. Basically. And yeah, I''ve tuned hundreds of cars, including several SC and turbo LTs. A few guys on here are pro tuners, so its not like you're talking to a bunch of novices.
And yes, you are correct, the tables arent AE, but PE functions in basically the same way. The major difference being AE is based on rate of change.
I would assume with our experience, you are capable of tuning a LT as a 2 bar system?

KVU

iTrader: (1)

Not trying to get into a pissing match. But AE and PE is not even close to the same thing. AE events happen according to the throttle blade movement. Once in PE, AE doesn't exist. PE is used for 100% throttle, AE for transitional changes. Ever heard of an accelerator pump? This is one reason I dont post much. Someone that has tuned hundreds of vehicle should know the difference, and I'm not going to debate it. WOW!

edcmat-l1

iTrader: (10)

YEP. I know exactly what an accelerator pump is, as well as the dif between AE and PE. If you'll read my post entirely, it even says AE is used for rate of change. Quick changes in TP or MAP.
The similarities between the two are enrichment none the less.
PE is for WOT, AE is for transitions of TP or rapid changes in MAP.
PE can and is used for acceleration enrichment, just as AE or an accelerator pump.
No pissing match. It is what it is.
The factory ECMs pretty much all use PE, the stand alones (dfi, fast, etc) use AE.

Fire67

iTrader: (3)

Wow, alot of information since my last post...
To answer some questions:
-96 (OBD2) LT1 Trans Am
-Yes I'm using a MAF (blow throug), I know it's not ideal... but up untill recently, this car has always been tuned by a Pro tuner here in FL, Im incredibly new to this.
-Going by some of my datalogs, the MAF is maxed out already as soon as I get into boost. When on the trans brake @ 4000 rpm the gauge shows 7-8 psi. Never logged any data when on the 'brake though... So I'll have to try and see if this boost level is maxing out the MAF.

Anyway, leaving work now. Thanks for all the info guys, please keep it coming. I've got a bunch of stuff to go try out now. So I'll get back to you guys when Im done.


-I would like more info on a 2bar SD setup. I had considered this before, but the motor gets 15psi now with a leaky Procharger ProFlow bypass valve. Whenever I put the other valve on it, its going to go above the range for a 2bar MAP. How would that affect operation?

Fire67

iTrader: (3)

Hey all,
I didnt get to do much with the car this weekend, but I did go into LT1edit and browse around a little bit. I should have said this last time, but I forgot. To end the match above, LT1edit does not have an AE table but a PE table.

I did some searching on the 2bar speed density idea, and I'm liking what I see, so its something I'll definitely look into doing in the near future.

I tried to launch the car without the methanol, instead of stumbling... It started to pull then broke up. Sounded like detonation to me, the data log didnt show any knock activity though. So i need to make sure the damn sensor is plugged in and try it again.

Will do some more experimenting this afternoon and get back to you guys with more definitive results.