Drag racing launching question/problem

Pocket · #1 Mon, May 10th, 2010, 10:58 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, 11:48 AM

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, 12:11 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, 12:56 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, 01:04 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, 04:54 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, 05:09 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.

Pocket · #8 Mon, May 10th, 2010, 05:53 PM

Thanks Cody. I'll see what I find. Still gotta figure out how to quit blowing my intercooler boots off every time I attempt a shake-down run.

GTS · #9 Mon, December 13th, 2010, 01:17 PM

I actually have some input on this. I've had this exact thing happen to me and it is not your transmission shifting. When it happened to me I described it exactly as you did initially thinking the transmission was shifting but it is not. While it does seem to make sense that if it shifted it would want to lurch however to the contrary it actually doesn't matter what gear the transmission is in. If the transmision sin't spinning (you moving forward) the gear is irrelevent and all that is going on in before the stationary input shaft which means what is going on is all in the TC.

I actually destroyed a TC doing this. When I talked to Brian at BTS he said what's happening is it's sucking the oil pan dry of oil then something in the TC wants to lock up. I don't think it's the clutch locking and I didn't understand what all it was but I've had this same thing happen when I was doing a tranny service and tried to put the transmission in gear before it had a chance to get the fluid flowing completely through the transmission.

You might want to call your tranny builder for a better explanation of whats going on but it's not the transmission shifting.

When I busted the TC doing this it sounded like a tin can with a bunch of bolts in it and it also locked up solid so as soon as I put it in gear the truck was rolling and if you hit the brakes to stop it it would kill the engine.

I suggest not spooling up so quick. Watch the other driver and as soon as he lights up the 2nd set of staging light start spooling. when I did this I would roll into the first set of lights, start spooling it then roll into the 2nd set of lights. This was just to much spool up time and caused the issue.

***Power Hungry*** · #10 Mon, December 13th, 2010, 03:07 PM

I wonder if a deep sump pan may also help this. You're probably already running one, so that would make the previous statement false.

Another thought is that the TFT is elevating during staging and causing the trans to shift into the default failure gear... 2nd. Any idea what the TFT is rising to?

Anyway, this is a complete mystery to me. I've never heard of this before so we'll need to have some more input in order to come to a resolution.