Drag racing launching question/problem

Pocket · #1 Mon, May 10th, 2010, 11:58 AM

I've had this happen twice when at the race track. I go to spool up at the lights, and the guy in the lane next to me takes a second or two longer to stage than I was thinking, and suddenly my truck will upshift into 2nd gear before I've even launched.

So looking under the functions, there is a setting called "Upshift Speed w/failed VSS". I'm assuming that the reason my truck upshifted was because it thought that my VSS failed. So if I raise the RPM's across all the throttle positions in this map, will that prevent it from upshifting when I'm staging? Or is there another map I should be looking at?

My thinking is that if I raise this to an RPM that's higher than what I launch at, then there won't be an upshift while I'm staging. Am I correct?

theSLEEPER · #2 Mon, May 10th, 2010, 12:48 PM

Quote:

Originally Posted by Pocket

I've had this happen twice when at the race track. I go to spool up at the lights, and the guy in the lane next to me takes a second or two longer to stage than I was thinking, and suddenly my truck will upshift into 2nd gear before I've even launched.

So looking under the functions, there is a setting called "Upshift Speed w/failed VSS". I'm assuming that the reason my truck upshifted was because it thought that my VSS failed. So if I raise the RPM's across all the throttle positions in this map, will that prevent it from upshifting when I'm staging? Or is there another map I should be looking at?

My thinking is that if I raise this to an RPM that's higher than what I launch at, then there won't be an upshift while I'm staging. Am I correct?

Wow, I don't have any input, but that's nuts!! What happened?? Just lugged the engine down?

Pocket · #3 Mon, May 10th, 2010, 01:11 PM

Quote:

Originally Posted by theSLEEPER

Wow, I don't have any input, but that's nuts!! What happened?? Just lugged the engine down?

Yeah it would lurch forward on the shift, then lug the engine. When it happened, I just took my foot off the brake and made a crappy red-light run down the track.

First time it happened I nearly crapped my pants.

theSLEEPER · #4 Mon, May 10th, 2010, 01:56 PM

I don't blame you! I guess all of the other non-self tuners have thought of that, LOL. I know with PHP and DI tunes, I've gone WOT for a about a second at the light after holding around 1600 for 5+ seconds and never had that happen.

***cleatus12r*** · #5 Mon, May 10th, 2010, 02:04 PM

Give it a shot, Pocket. It can't hurt anything. Bill is on the phone (imagine that) or I'd bother him about it. I'll get with him when he's done.

Another thought is this.....what is your 1st gear TCC apply speed? I'm thinking that if the transmission did shift to second, then you should have had an RPM change, but it definitely shouldn't have pulled through the brakes or "lugged" the engine......

Pocket · #6 Mon, May 10th, 2010, 05:54 PM

This happened on my old tunes from Jody. With the A/D counts on the throttle at 504 and higher, the 1st gear TC lockup speed was set at 16 mph. Anything below 504 was raised all the way up to 127.5 mph.

If the TC locked up, then it would make sense as to why it lurched forward like it did. So did it shift into 2nd and then lock, or do you think it locked the TC in first while I was spooling up?

I'm still going to try changing that table to see what happens. I might do it on my old tune to see if it makes a difference. I know how to duplicate the launch problem... just hold 1800+ RPM for longer than about 5-6 seconds.

***cleatus12r*** · #7 Mon, May 10th, 2010, 06:09 PM

Quote:

Originally Posted by Pocket

This happened on my old tunes from Jody. With the A/D counts on the throttle at 504 and higher, the 1st gear TC lockup speed was set at 16 mph. Anything below 504 was raised all the way up to 127.5 mph.

If the TC locked up, then it would make sense as to why it lurched forward like it did. So did it shift into 2nd and then lock, or do you think it locked the TC in first while I was spooling up?

I'm still going to try changing that table to see what happens. I might do it on my old tune to see if it makes a difference. I know how to duplicate the launch problem... just hold 1800+ RPM for longer than about 5-6 seconds.

Curtis,

It's impossible to say what is actually going on...and it can even be so stupid as a mechanical transmission issue where the pump isn't supplying enough fluid under that load (since it's raised to such a high pressure under WOT in 1st) to hold the torque converter clutch off of the backing plate.

I'd put a scanner on it and see what is being commanded.