Shift Time, what's the point?
Thread Starter
Instructor
Joined: Jun 2004
Posts: 190
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Shift Time, what's the point?
Relevant Mods:
bolt on's
High stall non-lockup converter and shift kit (shifts VERY quickly)
3.91 ring and pinion
mail order tune (not happy with it).
I'm trying to get my car to run decently. Currently the problem is when the car tries to shift, it always bogs and misses and won't accelerate. So, I was looking at my datamaster readout, and noticed that the computer pulls fuel at 60 mph (the duty cycle goes from 83% to 50%). Then looking at tuner cat, I see that's exactly where the 2-3 shift point is, but the car doesn't shift untill 67 mph. So more probing around, and I find shift time tables. The 2-3 shift time is 6.375 sec. That seemed long to me so I shortened it to .72 second (at 100%tps) and bumped the shift point to 65, flashed and redata logged the car. The data log shows the car pulling fine now until 65, then it does the same thing as before though not nearly as bad.
Now the point: I was thinking of reducing the shift time even more, since this is where my car has all sorts of problems (and shortening it up seems to help), but was wondering if there will be any detrimental effects to the transmission (or engine). My guess is that the shift time variable is suppose to reduce power through the transmission during the upshift.
Thanks for taking time to read this.
bolt on's
High stall non-lockup converter and shift kit (shifts VERY quickly)
3.91 ring and pinion
mail order tune (not happy with it).
I'm trying to get my car to run decently. Currently the problem is when the car tries to shift, it always bogs and misses and won't accelerate. So, I was looking at my datamaster readout, and noticed that the computer pulls fuel at 60 mph (the duty cycle goes from 83% to 50%). Then looking at tuner cat, I see that's exactly where the 2-3 shift point is, but the car doesn't shift untill 67 mph. So more probing around, and I find shift time tables. The 2-3 shift time is 6.375 sec. That seemed long to me so I shortened it to .72 second (at 100%tps) and bumped the shift point to 65, flashed and redata logged the car. The data log shows the car pulling fine now until 65, then it does the same thing as before though not nearly as bad.
Now the point: I was thinking of reducing the shift time even more, since this is where my car has all sorts of problems (and shortening it up seems to help), but was wondering if there will be any detrimental effects to the transmission (or engine). My guess is that the shift time variable is suppose to reduce power through the transmission during the upshift.
Thanks for taking time to read this.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 190
Likes: 0
I just did another data log on my car after decreasing the shift time again, which didn't make anymore of an improvement (I guess raising the shift point probably made the inprovement). But I noticed that as soon as it hits the shift point mph, the right side short term BLM jumps from 128 to 131. After that, it takes almost three seconds for the O2's to get back around 880 and the duty cycles to be within 2% of eachother. If anyone wants to take a look, I'll email them the datamaster file.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
I don't know what the shift time tables mean, either. Been looking on the web for info on the tranny tables for a few years and there's not much out there.
The 6.375 is clearly not seconds. Some people set the entire table to 6.375, since the performance table has that value in all locations.
Another bit of trivia - the hypertech doesn't change this table.
What's the source of your problems? Did this start when you installed the converter?
The 6.375 is clearly not seconds. Some people set the entire table to 6.375, since the performance table has that value in all locations.
Another bit of trivia - the hypertech doesn't change this table.
What's the source of your problems? Did this start when you installed the converter?
Thread Starter
Instructor
Joined: Jun 2004
Posts: 190
Likes: 0
My problems started after I put in a new cam and had the computer mail order tuned. It would always miss top end right about where it would shift, and continue to bog and miss into the next gear. I thought coolant contaminated the opti when I took it off to swap the cam, so I put a dynaspark in my car (didn't fix it). Called the tuner, flat out denied that there would be anything wrong his tune, my car must be seeing knock retard or not getting enough fuel. LONG story short, put all new fuel system components into the car (255 lph pump, adjustable regulator, injectors, filter) and had several mechanics scan the car to see if any sensors were failing, but to no avail. Finally got a laptop so I can data log the car and I can't figure out why it still misses around the shifts. Right after the shift point, the right side BLM goes lean for no apparent reason. The duty cycles are around 86%, the o2's are 880 +/- 15, and it only sees 1 degree of knock retard. I don't know what else would cause the BLM to go from 128 to 132 right after the shift point mph.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
What cam?
Did you have the converter, shift kit and gears before the cam and it was working fine?
Do you have a copy of your stock tune that you could install to see if that changes anything? Or at least to see what is different in the new tune?
I'd start a new thread in C4 tech laying out the whole story with everything you've done starting with the cam change. You'll get a bigger audience there.
Did you have the converter, shift kit and gears before the cam and it was working fine?
Do you have a copy of your stock tune that you could install to see if that changes anything? Or at least to see what is different in the new tune?
I'd start a new thread in C4 tech laying out the whole story with everything you've done starting with the cam change. You'll get a bigger audience there.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 190
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The only mods I did at the same time were the cam swap and reprogrammed the computer. Before that, everything was running fine. Since I mailed out my computer, I don't have a stock bin to compare what the changes actually were. So far, with my nosing around the bin file, I found the injector multiplier were way off (one was .00 and another was.43). After I got that closer to 1.00, the car ran MUCH better, but still misses when it tries to shift.
Anyways, thank you for your for your help thus far, and I'll probably start another thread like you suggested.
Anyways, thank you for your for your help thus far, and I'll probably start another thread like you suggested.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
I think you might check the fuel presure.
If you change shift points you will need to add fuel to compensiate for the increase in MPH,you are trying to change shift timing and you need to be changing the MPH .
If you add about 2 to 3 psi on the fuel presure you should notice a difference.Your trans is not shifting because the engine has not reached the proper presure in the valves in the trans to make the clutches ingauge.
This is only my thery of what the engine is doing,based on ,I did the same thing and it took a long time to make it right.
No one could help I had to figure it out.
I just added fuel and that reset the injector pulse width and bang it started shifting right .After that I just raised or lowered the MPH to adheive what I wanted .
I have seen some that could not figure it out just install a modulator on the trans and that worked for them .
If you change shift points you will need to add fuel to compensiate for the increase in MPH,you are trying to change shift timing and you need to be changing the MPH .
If you add about 2 to 3 psi on the fuel presure you should notice a difference.Your trans is not shifting because the engine has not reached the proper presure in the valves in the trans to make the clutches ingauge.
This is only my thery of what the engine is doing,based on ,I did the same thing and it took a long time to make it right.
No one could help I had to figure it out.
I just added fuel and that reset the injector pulse width and bang it started shifting right .After that I just raised or lowered the MPH to adheive what I wanted .
I have seen some that could not figure it out just install a modulator on the trans and that worked for them .
