Shifting problem>>Tuning

[TheGr8Schlotzky]

I swapped in my 97 pcm today and did a few things. The only thing I change by way of shifting was taking the shift durations down to .2. I was getting a problem of a "double shift" at 2-3 but we worked it out. It shifts fine at any variation of partial throttle, and shifts great at WOT except in the following cases:

When accelerating normally to anything below 20mph, and flooring it at that point, it shifts down quickly and goes through the gears just fine. Now, if you accelerate normally to ~25 -+4-5, and floor it, it down shifts just fine and goes on it's way to 2nd, but when it hits shift point, the acceleration stops, and the engine sounds as if it's bouncing off the rev limiter.

When accelerating normally to ~30- ~35, if you floor it at this point, the engine rpms sound as if it down shifted normally, but the acceleration is very mild for a about a second, and then it grabs and goes off just fine.

any ideas?

[ssms5411]

Re: Shifting problem>>Tuning

Have you corrected for gear and tire size? I only ask because the pcm auto scales for shift points.

[Meatyshells]

Re: Shifting problem>>Tuning

how old is your trans? i had that problem, my trans was bad and the added shift pressure caused it to slip. Would almost always slip from 2-3 shift and only slipped when it was really hot from 1-2

[TheGr8Schlotzky]

Re: Shifting problem>>Tuning

Yeah, I calculated the tire size and gear ratios in.

I don't believe it to be a problem with the transmission because it never did this before the tune, and every shift except those particular instances are perfect firm shifts. I wouldn't call the first case a slip either, I would call it a downright refusal to shift.

[Meatyshells]

Re: Shifting problem>>Tuning

how old is the trans? cause my car did the exsact same thing, Would slip so bad it pinged off the rev limiter and refused to shift unless i let off the gas. It worked fine before because the shift pressure was lower. You bumped up the pressure and im pretty sure that is what is causing the bad shifts.
If the trans is in the 120k range i would say it's the problem

[TheGr8Schlotzky]

Re: Shifting problem>>Tuning

yeah, but it's ONLY if I accelerate normally up to 25-30 and THEN floor it. It shifts perfectly at WOT and any variation of partial throttle, as well as if i floor it at 5-20mph.

[bigbrian442]

Re: Shifting problem>>Tuning

Did you change any of the WOT MPH shift points? Remember both the WOT MPH and RPM have to be met for it to shift. You might try lowering the MPH for the WOT 1-2 shift.
When I tuned my car I dropped the shift time for 1-2 and 2-3 to .100 and 3-4 to .200.
I then raised the pressure until it shift nice and firm, but not hard.

You also might want to check your other trans tables against a stock tune to make sure something didn't get changed.

Brian

[TheGr8Schlotzky]

Re: Shifting problem>>Tuning

I was getting a double shift consistently at 2-3 because the MPH and RPMs weren't lining up properly. I had to lower the MPH through the whole chart to get those shifts working right. I have everything set to .2, as I've been told much lower may lead to some inconsistencies.

I have an update with some more precise numbers.. It will only ping off the rev limiter if it's ~24 - ~28. If above or below, it shifts right into first and shifts into 2nd no problem.

It will only do the slip shift at ~32-36, which is right about where the changes occur that tell the tranny to shift into 2nd at WOT instead of 1st. I think the tranny may be trying to shift into 1st, but realizing it can't, after getting a few mph from this high revving, shifts into 2nd, and grabs just fine. My assumption is that a look at the tables around that area in the down shift table should get me my answer for this, and I just need to tweak the mph around there.

I won't have a chance to look at anything tuning wise until next month, since that's the next time my club meets and another member is the guy who is tuning for me.

Opinions, suggestions welcome.

[ssms5411]

Re: Shifting problem>>Tuning

I left all the tranny tables stock. Except for the .200 and upping the shifts to 5900 rpms. I did mess with the MPH when I first did the tune and I was getting the same thing as you with it not shifting right. So I reset everything to stock and just changed what I said above. Works outstanding. You can always just flash it back to the stock settings if you need to. Good luck

[bigbrian442]

Re: Shifting problem>>Tuning

Reading the HPT and LS1tech boards .100 is the lowest you should go for shift times. I didn't like the way .200 felt. .100 works fine in my car.
You might try changing the down shift table so it only drops to second and not first at that point.


Brian

[TheGr8Schlotzky]

Re: Shifting problem>>Tuning

The wierd part, is that I downloaded a stock tune, and after flashing it on to the car, that's when I got the double shift 2nd to 3rd. I'll mess around some more with it and try re flashing it with a stock tune again and see if I can't see an improvement. I may drop my shift times some more as well after hearing that. What is your max pressure set at?

[bigbrian442]

Re: Shifting problem>>Tuning

96 PSI Thats as high as the pump can put out. The HPT forum is free. Lots of good info there. Also V6 tunning has its own sections for trans and motor.

http://www.hptuners.com/forum/index.php

Right to the forum. You need to be very careful using a unknown tune, people like to play.

Brian

[ssms5411]

Re: Shifting problem>>Tuning

I left my pressure stock, I think it is 90.