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04-30-2012
Ok ive been on the highway alot recently.... Noticed when i go to pass a car or to get on the highway, when i get on the gas the tranny doesnt down shift first.. Car just stays in the gear its in...?? Even at 4rpms.. Do i have a problem with my tranns..??!!
Car is a 2000 grand prix GT. 130k ish miles
04-30-2012
so ur saying ur car has never downshifted when u hit the gas no matter what speed u floor it at?
04-30-2012
Originally Posted by sLpGPGT
Yep pretty much.... Dont really drive it hard so i havent noticed till just recently..
05-01-2012
When coming to a stop from any speeds, it downshifts normally?
05-01-2012
Ya doesnt do anything unnormal that i can notice.. All is smooth. I do notice when i take my foot off the gas and then go back to the gas u can hear something clank..??!! Not loud but u can really tell when ur driving around 30 - 50isg mph...
05-01-2012
Have you changed the MAP sensor? Any DTC's?
05-02-2012
Nope on the map, did change the maf sensor last fall.... And that really brought up my mpgs!!! Lol
No codes either... If tranny was bad would i see a service engine light..??
05-02-2012
Let's see if anyone else has an opinion on the MAP sensor.
Yea, a major problem may set a DTC. So you're saying you had the car scanned and they're are no DTC's; no CEL and no historic codes?
05-02-2012
Here's the funny thing about DTC's that you notice when you start tuning or messing with the cars enough. Most transmission DTC's don't kick on the light. They set, the car might buck, scream and throw a tantrum...but those codes don't light up your life.
Our up and down shifting is computer controlled. Therefore if you go up, you should be able to come down. Hence my question about it downshifting for stoplights etc. It does downshift,
What rpm is 70mph driving normally for you?
I'm starting to think that either you are in 3rd and the 4th clutch hub is shot, or you are having a sensor issue. Which.. my pal Rico has already eluded to.
05-02-2012
Rpms at 70mph are 2500 after awhile on the highway it does seem to back down to around 2300 after driving for a bit.
Last edited by tc300; 05-02-2012 at 04:27 PM.
05-02-2012
Only 2 codes ive ever had was a misfire..changed a coil pack and a maf problem..
05-06-2012
Anybody else wana chime in....??!!
05-06-2012
So at 70mph you feel it slip into overdrive every once in a while? The PCM should command the TCC at about 55mph or so.
If your RPM is around 1900-2100 at 60 mph then you should be in overdrive.
If RPM is 2300-2500 at 60mph then you are stuck in 4th gear.
Since there's no DTC then I would assume that the computer isn't commanding the TCC.
This may be due to a vacuum leak or a bad MAP sensor. Vacuum and MAP sensor are integral to PCM for tranmission control.
I hope the problem is a vacuum leak or a bad MAP and not the valve body in the transmission.
05-07-2012
Chuck...he's a GT aka 3.29 gear ratio. His speeds etc sound about right for 4th TCC locked.
Easy way to test TCC is holding your foot steady on the throttle at 70mph once it does that secondary drop down, Tap the brake pedal with your left, just enough to kick on the light. You should see the rpm jump 200-500 and then go back down a moment after the foot is removed from the brake pedal. That's the TCC disengaging and reengaging.
To tell if you get 4th.. simply pull the gear selector to 3rd and see the rpm go up close to 1,000rpm.
When you are doing 70mph and the car is sitting at about 2100-2300, if you stuff it to the floor, what rpm does it go to immediately?
05-08-2012
Yes every thing you said the car does correctly.... 2marow i will hit the highway and do 65 or 70 then floor it to see what the rpms go to. I know for a fact the car DOES NOT down shift first.. I hear a metal to metal when i take the car out park to back up and put it in drive.. A clank for reverse and a clank when put in drive. Gona try n see if i can record the sound. Maybe i can email it to you.
05-08-2012
Overdrive works 100% for sure... Just want to know why when i get on it, it doesnt down shift first...
That is my question
05-08-2012
What do you mean when you say "down shift first"? Are you saying that the down shift is delayed or it just doesn't down shift at all?
I think that the PCM controls the transmission's "kickdown" via the TPS sensor. You could check the TPS output signal for smoothness and voltage. The best way to check transmission control is with a scanner. If the PCM is commanding TCC off and/or down shift to third when you mash it to the floor then there may be something wrong with the transmission internally.
05-08-2012
When your driving dont most/all car down shift when u put the pedal to the floor..?? Every one i have drove did it, well besides my hyundai genesis and a old 350z i use to have cause they were sticks.... Lol
When u mean scanner, are talkn the same one used for cel/ces lights...?? Or is there a whole different scanner??
05-08-2012
Depending on what you used to get the engine codes, it may be able to scan the car in real time and see things.
When you stuff a GP to the floor, it takes a moment, kinda bogs then downshifts and heads on down the road. It's not quite a perfect as say an old carb based motor with a true kick down cable that got the trans to downshift before the power kicked in. This is why manually downshifting if you plan on giving it a good blast on the highway is recommended. The 4th clutch hub in the 97-03's are weak and would usually suffer a failure when kicked at higher miles.
05-08-2012
Ok are you saying my tranny is on its way of going out...???
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