Slow 1-2 shift, 04 GMC

[sean3393]

Wondering if anyone could help me out.

After deleting all the TM on an 04 GMC the 1-2 shift is slower than stock @ WOT, firmer but slower. It drags through the shift, then sorta bumps into second. The 2-3 and 3-4 shifts are dead on though. At part throttle the 1-2 shift is fine, this problem just exists from about 3/4 to WOT.

I've played around with the shift times, pressure and force motor current, but still no success. One thing that did seem to make a difference was lowering the 1-2 shift RPM down to 5000, but then it doesn't pull as good after the shift so I raised it back up.

If anyone could take a look at the tune or give me some more suggestions I'd really appreciate.

I've checked out this thread. (http://www.forum.efilive.com/showthread.php?t=4456) It helped a little.

Thanks

[cmitchell17]

The stock trans wont shift hard on the 1-2 at WOT.
No matter how much you put the pressure to it.

Your going to have to put in some torque reduction or your trans will just slip without it. The fastest I can get mine to shift at WOT is .6seconds with my stock trans. That with about 20%TR at 300ft.lbs.

I just noticed that you looked at my other posts about this.

I think youll need a servo to get the shift your looking for.


What is your delievered torque at WOT. Although I do see the PCS solenoid read 90psi max when the WOT 1-2 happends, I think the low delievered torque readings I have might have something to do with it. Mine never goes above 300ft.lbs. I have another stock 5.3 log that never goes above 300 also.

Just wondering too, what kind of timing are you running is your truck stock?

[cmitchell17]

Sorry just noticed you posted your tune ill look at it.

[ChipsByAl]

Have you tried disabling the abuse management? D2001 thru D0301 is the area to edit. If it helps you can enable it and decrement how much it is used in the D2004 table. I would plan on having your transmission beefed up if you leave it like that.
Al

[cmitchell17]

It seems like it requires almost no pressure to make the 2-3 shift hard. And takes also for the 1-2

[cmitchell17]

I did notice anything from abuse mode. I turned it all off on my stock trans but i still have torque reduction.

[ScarabEpic22]

Get a Vette 1-2 servo for like $50 installed. I have one in my TrailBlazer and am running 0 TM, 0 shift times, and slightly adjusted line pressures (mostly a hair reduced for a little softer shift), and it shifts like a BEAST. I get wheelspin at WOT from 1-2 and the shift is fast, firm and comfortable. No more huge bang into 2nd. BTW, I have the 4.2L I6 motor, I dont even have a V8 (although I beat on Explorers and Durangos with them...).

[sean3393]

thanks for the replies so far. Forgot to mention that the truck is a 2wd w/ the 4.8L, but you prob caught that from the tun file. I'll try more of a stock curve on the pressure and add some TM back to the 1-2 and go from there. Erik, i know what you mean bout the vette servo. I put one in my 98 silverado, all i can say is WOW!! Night and day difference from stock.

cmitchell, I used the excel spreadsheat you sent me for the HO timing table adjustment. I believe i weighted it 25% towards the optimal timing. That along w/ PE changes really woke up the truck.

[cmitchell17]

Probelm with me is I can't tell a diffrence no matter what kind of timing I have. I guess its just me though, so ill trust that the Optimal timing table is right.

I get knock with just about any timing if I dont have 93 in. What about you?

[sean3393]

I don't have too much of a problem w/ knock. Sometimes there is a 5 deg. retard, seems to be random and usually just when coming out of WOT, so it could be something to do w/ burst knock. Other than that i don't see much knock retard. If the quality of the fuel isn't too good though it can cause some knock retard, i've been through this a couple times. Have you messed w/ any of the burst knock settings??

[cmitchell17]

Hey I got another question. What do you do with your fuel correction spark mixture?

Im going to try taking most of the timing out from it, and run 60-80% optimal timing.

Becuase if the optimal timing is what the final timing should be, then what should the final timing be in PE with a richer fuel mixture?

[sean3393]

just depends on how rich you go, w/ more fuel you can add a bit of timing. I usually have anywhere from 1-3 degrees added in from the fuel mixture spark correction table. I watch the log for knock and take a little out if there is any. I know you've heard it before, but w/o dyno tuning you never really know what optimal timing is.