tuning an auto vette

[minytrker]

I tuned an auto heads and cam vette the other day and it runs really good. The only complaint the customer has, which I never caught when I had the car is if you punch it real quick and let off from a slow speed almost a stop and let if rev up real fast when it comes back down sometimes it will die. It does it only at low speeds because I checked it while drving and it doesnt do it. It revs fine in park or neutral and will come back down and stop at idle perfect. What do I have off? It also will surge about 200rpm one time when you put in gear but then its fine. Is this normal for cammed auto's?

[white2001s10]

vettes use the throttle as the IAC. I'd log while it's doing this to see what exactly is going on.

[minytrker]

I will check it. The hard part about it is the only time the car does it when your just hitting the gas real hard from a stop or low speeds and letting off completly. Which I still don't know why the owner does this but thats besides the point.

[TAQuickness]

I think you need to look at the throttle cracker decay rates in the upper RPM range. IIRC, it will want to decay a bit faster from hi RPM to avoid hanging. IN your case, it's decaying too fast causing stalling.

[Doc]

Here's an idea- don't know if it will help but if you are in gear and your TP is less than 1.19 (stock setting for Fbody Gen-Param) then you are using the base spark table if you are now "strattling" a higher/ different part of the table that the spark may be to far advanced so when you "punch" it from a slow roll or near stop it dies. I had issues with the pcm "twicthing" in the base spark table afer my H/C/I swap on my 98ZA4. Scanning revealed the pcm swinging btw a higher (~35) cell and a lower (~28) cell that normally while in gear at TPs below 1.19 the car would never see stock but since the idle had increased overall because of the H/C the car found it'self in this weird state. This would manifest it'self in all kinds of stalling, surging, freaky behavior but only at the low TPs - as soon as I would give it more TP bamo it would jump back to the HO table and be fine. I screwed around endlessly with follower, cracker you name it air tables until this. The better I get at using the scanner the easier tuning becomes. This was without using the Moates controller since my 98 is not ready for it...yet.

[minytrker]

I think you need to look at the throttle cracker decay rates in the upper RPM range. IIRC, it will want to decay a bit faster from hi RPM to avoid hanging. IN your case, it's decaying too fast causing stalling.


Thats what I think it is. It does decay a little slower in P or N vs doing this sudden punch and letting off. If you don't let off it takes off like a bat out of hell, so I really don't think its a timing issue.. Im looking at the the decay where it is doing it and its 0.0016 and 0.0019 in gear.