Okay, so my 1998 TransAm is at about 75,000 miles. It is all stock internals, but I have the SLP air lid, 92mm Air Intake Manifold and Throttle Body from FAST, and full exhaust (Long Headers, ORY, Borla.) After installing the AIM and TB, I relearned my idle, my TPS, even reset the PCM... but no matter what I do, this car will NOT downshift from 4-3 or 3-2 when I need it to, especially at WOT. I even replaced the TPS. Sometimes it randomly magically works, but sometimes I go to drop it in powerband, and the car either makes a shutter noise in the back wheels, or just slowly and embarssingly accelerates from the very bottom of high gear. And then, sometimes, if I hold the throttle to the floor the whole time, it will SUDDENLY downshift at the TOP of 4th gear into 3rd or 3rd in to 2nd when I've already reached my speed, and I have to come off the throttle because now it's too late to shift... I'm already at the speed! And not trying to wreck, etc.

This is extremely annoying (and embarrassing, car is making a bunch of noise and not going anywhere.) When she DOES downshift, she FLIES, I love this new intake manifold. (I have a 1998, so I came from LS1 manifold, not LS6.) But that's only 33% of the time that it will actually kick down gear. The trans fluid is at the correct level, I even filled it a little more, and nothing. 2/3 of the time, she just won't hammer down gear like she used to. Did the new throttle body or intake manifold **** up my shift points? Can a tune from Frost fix this? (I'm on stock tune with all these bolt ons.) Or is my transmission *mechanically* dying which I CANNOT afford to fix.

Oh, it also upshifts way too early now after the TB/AIM install, like WAY too early, unless I hold WOT. If I'm even a little under WOT it will shift in like the 1900-2100 RPM range.

 

I doubt it is a internal transmission issue.

I would replace the vehicle speed sensor (vss)
and make sure your tps is reading correctly.

 

I would look more into your tps.

 

Put the stock throttle body on and try it.
The tb is allowing more air in at a lower tps, it's tuned to shift off mph and tps.

 

Agree with the above. If you've ever looked into "bluecat's" tuning helper for transmission tuning...you can see the tables will make pretty drastic swings for a throttle body change.

Either go back to stock throttle body, or get your shift points tuned appropriately for the new setup

 

That makes sense, but I think it's impossible to use stock throttle body with this intake manifold. Different bolt pattern. I guess TUNE TIME IT IS!

 

Do you have a volt meter?

You should not need a tune after a throttle body and intake change. You need to get your tps right

 

You should have around .5v with the throttle closed.
You will be around 4.7v at wot.

With the fast, chance's are you need to remove the stop on the bottom side of the throttle position sensor then make the two screw holes oval so you can turn the sensor a bit with the screws loose. You are not seeing 100% during wot.

 

How does the trans act if you manually shift down into the gear you want before you stab the throttle?

After re-reading I think I somewhat agree with Cayenne...WOT is WOT so it should downshift.

if your part throttle shift points were weird, then I would say tune time. Because for the same amount of delta air, you need less throttle input. Which could make the car drive odd based on the tps vs speed vs gear tables

So, use the volt meter or a scanner and make sure you're getting proper tps...sorry if I sent you down the wrong path

 

I might have a volt-meter. I DO have a OBD-II blue tooth hook up and the pro version of Torque, so I can see TPS measured in %. I'm not sure if I can look at a gauge based on voltages. If not, I'll try to find a volt-meter.

Also, the one time I shifted from D in to 3 it down shifted, but it felt kind of harsh. Is that safe to do in automatic? I always thought it was bad for the car since I can't clutch and rev match. I can try 3->2 if it's safe, because that is just as big of a problem. (Only working 1/3rd of the time.)

 

You need a volt meter.

Short answer you will be fine manually downshift. I do it all the time with a close rev match.

On a 4-3 downshift the 2-4 band releases and the forward sprag engages.

 

Okay, I'm going to pick up a multimeter at Autozone. I'm pretty noob, what exactly do I do with this? I'm sorry for having so many questions. I crimped all the wires for my own stereo before, so I'm not a TOTAL idiot, but I've never worked with multimeter or anything like that before. I can't imagine it's too hard, I'm just not sure how to wire this all up to check the voltage on the TPS.

 

This will be quite easy and straight forward.

There will be 3 wires coming out of the tps. Blue, Black and gray. You will take the red prong from the volt meter and insert it into where the blue wire is going. Ground the black volt meter prong anywhere metal. Have the key at the On position. Post back your results. Couple pictures below

 

At closed throttle it hovered between 0.3v and 0.75v, and at WOT from pedal, it maxed at 3.3v................................ This is a new TPS, too, and I relearned it.

 

UPDATE: I tightened the throttle cable with that little adjuster, slightly adjusted the throttle door (so that it was tight but not resting ON the cable) and re-learned idle and TPS. I'm getting 100% WOT!!! It seems to kick down every time now (although, driving it a few days I will know for sure.) The early shift problem is still there, but I'm wondering if that is more from being on stock tune like you guys said?

 

It should not short shift from a throttle body and intake change. It should shift at the same points it did previous.

 

Hm. Well, at least I got one problem solved. I would like to buy both of you a beer. lol

Now on to the short shift problem...

 

More air less tps%

 

On all tests I was getting 4.7v and reading 100% throttle at WOT while the car was off, and the car STILL wouldn't downshift at 100% throttle confirmed on scanner. It's shifting a lot more frequently, like 90% of the time instead of 20% of the time, but it's still sometimes just hanging at really low RPM and high gear, even though I'm at 100% throttle (according to Torque/OBDII.) Sigh.

 

I'm starting to think it really is the tune, because it downshifts flawlessly if I manually bring it in to 3rd, and I confirmed 100% throttle many times without it shifting. And the shifting feels just ... off, like I can almost predict it because it is off by the same amount when it doesn't shift or shifts early, it isn't random in location. But she's running strong, and launches like a champ. Ugh. I don't mind getting a tune, I just don't want to MASK an ACTUAL problem with a tune. But I have a new IAC/TB. Relearned. Reading 0% and 100% consistently. Voltage is correct now. Throttle cable is tight. She's idling strong. She's purring all across the RPM ranges (ever since I replaced both O2 sensors.) I don't get it (other than if you guys are right about it being from stock tune with a larger air flow.)