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Old 09-27-2011, 09:25 PM   #1
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Default No downshift when I punch it???

I have searched and searched and couldn't find guidance on this. Any idea anyone? When I floor it it just accelerates like normal without downshifting. I have used the max energy programmer...it helped a little. Eventually going to get a pro tune but was trying to get everything working before I take it in. BTW this is a 95 Z-28 that I swapped a 2000 Z LS1 into. I am using the LT1 trans. It is the pwm one. And....I cannot tap the brake and get it to downshift.....


Side note: how do you know when the trans hits lock up?
Thanks

Last edited by waxenate; 09-27-2011 at 09:30 PM.. Reason: added
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Old 09-28-2011, 11:20 AM   #2
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My guess is is it is the TPS (throttle position sensor). Does it downshift from 4th to 3rd when you drop the gear manually? Don't go any further than D3 when manually downshifting though as that WILL blow the tranny.
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Old 09-28-2011, 02:55 PM   #3
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Thanks! Will check that!
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Old 09-30-2011, 01:18 PM   #4
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check the transmission pressure switch change it, then try,,,
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Old 09-30-2011, 02:07 PM   #5
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Is it slipping at all? Are you getting a slide-bump type shift or an RPM flare on upshifts? Is it upshifting normally?
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Old 09-30-2011, 02:24 PM   #6
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Stock tune requires you to be over 96% TPS to kick down
2-1 above maybe 10 MPH (gear dependent). If your pedal
doesn't pull to that extent (I've seen cars that won't even
get past 90%) then you won't kick down. The handhelds
I've seen only mess with WOT shiftpoints and you maybe
are not getting to WOT.

Have somebody (or your friend Mr. Cinderblock) mat the
pedal and go measure where the blade edge sits in the TB
face. If it's not making it to dead center then you have
some mechanical work to do (recommend just bending
the gas pedal arm for more draw length).
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Old 10-02-2011, 09:04 AM   #7
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you will know that your in lock up after the 4th shift, you should get anywhere from a 4-600 rpm drop once lockup occurs. and as far as touching the brake while driving to get a down shift that normally only works for getting the car to come out of lockup, if your not getting a 4-600 rpm increase when you hit the brake then your torque converter could be sticking on for various reasons, could be a valve body problem.. i have seen a few of these with problems of worn valve body bores and such that cause the tcc to stay engaged when the car hits 4th gear.. I'd take it to a trans shop and have the do a free evaluation, there are so many possibility's that its going to be hard for someone to totally send you in the right direction without driving the car and watching live date on the trans
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Old 10-02-2011, 09:11 AM   #8
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Thanks for the info...figured out I have a tps problem. Getting high input. Also no power to my maf. Coolant temp sensor is high output as well...think I have a wiring problem...any input anyone? Thanks
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Old 10-02-2011, 09:21 AM   #9
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yep check the wires from the pcm to tps, ect and maf. resistance should tell you alot there

and if all the wiring checks out id start with replacing the ect if its bad, check the resistance on it as well im going to get you some specs i will post up here in a few

you will have to save and print these because i dont know how to just make the show up in my post but the are all of the connector views for your 3 trouble sensors and PCM connector
Attached Thumbnails
No downshift when I punch it???-62648204.gif   No downshift when I punch it???-62648199.gif   No downshift when I punch it???-62648173.gif   No downshift when I punch it???-62648168.gif   No downshift when I punch it???-62648167.gif  

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Old 10-02-2011, 09:56 AM   #10
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Thanks T/A! I didn't mention but this is a 2000 Z-28 LS1 swapped into a 95 Z-28. Going to check reistence today. Also do you know anything about the little vacuum line in the harness? I think it plugs into the rear of the intake manifold.
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Old 10-02-2011, 10:24 AM   #11
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vacuum line could be something to do with hvac not 100% on that though id have to look into it more, ok yeah i didnt notice you said it was a swap did you use the computer and all? if so the diagrams will still be right just maybe wire color could be off i will check i looked it up for a 98 5.7 because im pretty sure they are the same as far as electronics go, but i will double check and if not i will update the schematics. and i will also see what i can find about the vacuum line post back in a few

Ok so i did give you the wrong schematics so here are the updates, and i believe the vacuum line your looking at goes to the map sensor housing right under or near the electrical connector
Attached Thumbnails
No downshift when I punch it???-86424298.gif   No downshift when I punch it???-86415728.gif   No downshift when I punch it???-86412247.gif   No downshift when I punch it???-83321487.gif   No downshift when I punch it???-83321486.gif  

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Old 10-03-2011, 10:21 AM   #12
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Thanks...that should be fun to slip on! lol Def need a mirror!
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Old 10-03-2011, 11:03 AM   #13
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Both of those issues (TPS and MAF) have a BIG impact on how and when the trans shifts. The computer takes input from those sensors to determine the correct shift points as well as to set line pressure in the trans. You definitely want to get that fixed ASAP before you burn up your tranny.
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Old 12-13-2011, 02:18 PM   #14
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I'm having a similar issue of the car not wanting to downshift but the TPS is brand new. What kind of resistances/ voltages are you supposed to see for the TPS? I think you're supposed to see ~5V a WOT, is that right?

It seems to buck a bit more in the 1-2 shift if I don't have the RPM's up.

It wasn't doing then when it was tuned but I know he did increase the shift firmness and that was back in July and it wasn't doing this.
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Old 04-15-2012, 01:21 PM   #15
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Waxenate, did you ever solve this problem? I swapped a '01 ls1/a4 combo into my '97 and I am having the same exact issues.
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Old 04-15-2012, 04:15 PM   #16
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Disregard, I figured out my problem. When I reworked my harness I didnt remove C100 pin E on the harness side, which is the tps signal wire. On my 97 C100 pinE on car side is the air pump, which I deleted anyways. So leaving thes 2 connected gave the tps a constant 12 volts causing the p0123 code. Car is much faster and shifts great now!
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Old 04-15-2012, 04:15 PM
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